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we 're told to solve and graph the solution for the system of equations right here . and the first thing that jumps out at me , is that we might be able to eliminate one of the variables . and if we just focus on the x , we have a 4x here and we have a 2x right here . if we were to just add them right now , we would get a 6x . so that would n't eliminate it . but if we can multiply this 2x by negative 2 , it 'll become a negative 4x , and then when you add it , they would cancel out . so let 's multiply this equation , this second equation , by negative 2 . so i 'm going to multiply both sides of this equation by negative 2 . and the whole motivation is so that this 2x becomes a negative 4x . and , of course , i ca n't just multiply only the 2x . anything i do to the left-hand side of the equation i have to do to every term , and i have to do to both sides of the equation . so the second equation becomes negative 4x -- that 's negative 2 times 2x -- plus -- we have negative 2 times negative y -- which is plus 2y is equal to 2.5 times negative 2 , is equal to negative 5 . i just rewrote the second equation , multiplying both sides by negative 2 . now , this top equation -- i 'll write it on the bottom now -- we have 4x minus 2y is equal to positive 5 . and now we can eliminate it . we can say , hey , look , the negative 4x and the positive 4x should cancel out , or they will cancel out . so let 's add these two equations . let 's add the left side to the left side , the right side to the right side , and we can do that because these two things are equal . we 're doing the same thing to both sides of the equation . so what do we get ? if we take our negative 4x plus our 4x , well , those cancel out . so you 're left with nothing . maybe i could write a 0 there . 0x if you want . and then you have your plus 2y and your negative 2y . those also cancel out . so you 're also left with 0y . and then that equals negative 5 plus 5 is equal to 0 . so this just simplifies to 0 equals 0 , which is true , but it 's kind of bizarre . we had all these x 's and y 's . everything canceled out . so let 's explore this a little bit more . let 's graph it and see what this 0 equals 0 is telling us when we try to solve this system of equations . so let me graph this top guy . i 'll do it in blue . so right now it 's in standard form . let 's put it in slope-intercept form . so we have 4x minus 2y is equal to 5 . let 's subtract 4x from both sides . i want the x terms on the right-hand side . so then i 'm left with negative 2y is equal to negative 4x plus 5 . now we can divide both sides by negative 2 . and we are left with y is equal to positive 2x , right , that 's positive 2x , minus 2.5 . so let 's graph that . the y-intercept is negative 2.5 . so negative 2.5 right there , and then it has a slope of 2 . so if we move up 1 , if we move up in the x-direction , if we move to the right 1 in the positive x-direction , we will move up 2 . so 1 , 2 . right there . and if we were to do it again , we move up 1 , 2 . just like that . so the line 's going to look something like this . i 'll try my best to draw a straight line . this is the hardest part about a lot of these problems . there you go . so that 's the top equation . now , let me draw the bottom equation . let me draw and i 'll do it in this green color . so this bottom equation was 2x minus y is equal to 2.5 . and we can subtract 2x from both sides . the left-hand side becomes negative y is equal to 2x plus -- or is equal to negative 2x plus 2.5 . now let 's multiply or divide both sides by negative 1 . and you get y is equal to positive 2x minus 2.5 . and let 's try to graph this , and you already might notice something interesting about these two equations . you try to graph this , the y-intercept is at negative 2.5 , right there . the slope is 2 . so it 's going to be this exact same line . and you saw that algebraically . i did n't have to graph it . these two lines have the exact same equation when you put them in slope-intercept form . that 's the first equation . that 's the second equation . so what this 0 equals 0 is telling us is actually that these are the same line . that these actually have an infinite number of solutions . any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . these are the same line . | any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . | how do i solve : y= x-4 y= -4x+26 using elimination ? |
we 're told to solve and graph the solution for the system of equations right here . and the first thing that jumps out at me , is that we might be able to eliminate one of the variables . and if we just focus on the x , we have a 4x here and we have a 2x right here . if we were to just add them right now , we would get a 6x . so that would n't eliminate it . but if we can multiply this 2x by negative 2 , it 'll become a negative 4x , and then when you add it , they would cancel out . so let 's multiply this equation , this second equation , by negative 2 . so i 'm going to multiply both sides of this equation by negative 2 . and the whole motivation is so that this 2x becomes a negative 4x . and , of course , i ca n't just multiply only the 2x . anything i do to the left-hand side of the equation i have to do to every term , and i have to do to both sides of the equation . so the second equation becomes negative 4x -- that 's negative 2 times 2x -- plus -- we have negative 2 times negative y -- which is plus 2y is equal to 2.5 times negative 2 , is equal to negative 5 . i just rewrote the second equation , multiplying both sides by negative 2 . now , this top equation -- i 'll write it on the bottom now -- we have 4x minus 2y is equal to positive 5 . and now we can eliminate it . we can say , hey , look , the negative 4x and the positive 4x should cancel out , or they will cancel out . so let 's add these two equations . let 's add the left side to the left side , the right side to the right side , and we can do that because these two things are equal . we 're doing the same thing to both sides of the equation . so what do we get ? if we take our negative 4x plus our 4x , well , those cancel out . so you 're left with nothing . maybe i could write a 0 there . 0x if you want . and then you have your plus 2y and your negative 2y . those also cancel out . so you 're also left with 0y . and then that equals negative 5 plus 5 is equal to 0 . so this just simplifies to 0 equals 0 , which is true , but it 's kind of bizarre . we had all these x 's and y 's . everything canceled out . so let 's explore this a little bit more . let 's graph it and see what this 0 equals 0 is telling us when we try to solve this system of equations . so let me graph this top guy . i 'll do it in blue . so right now it 's in standard form . let 's put it in slope-intercept form . so we have 4x minus 2y is equal to 5 . let 's subtract 4x from both sides . i want the x terms on the right-hand side . so then i 'm left with negative 2y is equal to negative 4x plus 5 . now we can divide both sides by negative 2 . and we are left with y is equal to positive 2x , right , that 's positive 2x , minus 2.5 . so let 's graph that . the y-intercept is negative 2.5 . so negative 2.5 right there , and then it has a slope of 2 . so if we move up 1 , if we move up in the x-direction , if we move to the right 1 in the positive x-direction , we will move up 2 . so 1 , 2 . right there . and if we were to do it again , we move up 1 , 2 . just like that . so the line 's going to look something like this . i 'll try my best to draw a straight line . this is the hardest part about a lot of these problems . there you go . so that 's the top equation . now , let me draw the bottom equation . let me draw and i 'll do it in this green color . so this bottom equation was 2x minus y is equal to 2.5 . and we can subtract 2x from both sides . the left-hand side becomes negative y is equal to 2x plus -- or is equal to negative 2x plus 2.5 . now let 's multiply or divide both sides by negative 1 . and you get y is equal to positive 2x minus 2.5 . and let 's try to graph this , and you already might notice something interesting about these two equations . you try to graph this , the y-intercept is at negative 2.5 , right there . the slope is 2 . so it 's going to be this exact same line . and you saw that algebraically . i did n't have to graph it . these two lines have the exact same equation when you put them in slope-intercept form . that 's the first equation . that 's the second equation . so what this 0 equals 0 is telling us is actually that these are the same line . that these actually have an infinite number of solutions . any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . these are the same line . | you try to graph this , the y-intercept is at negative 2.5 , right there . the slope is 2 . so it 's going to be this exact same line . | if you know that if 2 lines have the same slope and y-intercept , could n't you have multiplied the bottom equation by 2 and figured out that there are infinite solutions ? |
we 're told to solve and graph the solution for the system of equations right here . and the first thing that jumps out at me , is that we might be able to eliminate one of the variables . and if we just focus on the x , we have a 4x here and we have a 2x right here . if we were to just add them right now , we would get a 6x . so that would n't eliminate it . but if we can multiply this 2x by negative 2 , it 'll become a negative 4x , and then when you add it , they would cancel out . so let 's multiply this equation , this second equation , by negative 2 . so i 'm going to multiply both sides of this equation by negative 2 . and the whole motivation is so that this 2x becomes a negative 4x . and , of course , i ca n't just multiply only the 2x . anything i do to the left-hand side of the equation i have to do to every term , and i have to do to both sides of the equation . so the second equation becomes negative 4x -- that 's negative 2 times 2x -- plus -- we have negative 2 times negative y -- which is plus 2y is equal to 2.5 times negative 2 , is equal to negative 5 . i just rewrote the second equation , multiplying both sides by negative 2 . now , this top equation -- i 'll write it on the bottom now -- we have 4x minus 2y is equal to positive 5 . and now we can eliminate it . we can say , hey , look , the negative 4x and the positive 4x should cancel out , or they will cancel out . so let 's add these two equations . let 's add the left side to the left side , the right side to the right side , and we can do that because these two things are equal . we 're doing the same thing to both sides of the equation . so what do we get ? if we take our negative 4x plus our 4x , well , those cancel out . so you 're left with nothing . maybe i could write a 0 there . 0x if you want . and then you have your plus 2y and your negative 2y . those also cancel out . so you 're also left with 0y . and then that equals negative 5 plus 5 is equal to 0 . so this just simplifies to 0 equals 0 , which is true , but it 's kind of bizarre . we had all these x 's and y 's . everything canceled out . so let 's explore this a little bit more . let 's graph it and see what this 0 equals 0 is telling us when we try to solve this system of equations . so let me graph this top guy . i 'll do it in blue . so right now it 's in standard form . let 's put it in slope-intercept form . so we have 4x minus 2y is equal to 5 . let 's subtract 4x from both sides . i want the x terms on the right-hand side . so then i 'm left with negative 2y is equal to negative 4x plus 5 . now we can divide both sides by negative 2 . and we are left with y is equal to positive 2x , right , that 's positive 2x , minus 2.5 . so let 's graph that . the y-intercept is negative 2.5 . so negative 2.5 right there , and then it has a slope of 2 . so if we move up 1 , if we move up in the x-direction , if we move to the right 1 in the positive x-direction , we will move up 2 . so 1 , 2 . right there . and if we were to do it again , we move up 1 , 2 . just like that . so the line 's going to look something like this . i 'll try my best to draw a straight line . this is the hardest part about a lot of these problems . there you go . so that 's the top equation . now , let me draw the bottom equation . let me draw and i 'll do it in this green color . so this bottom equation was 2x minus y is equal to 2.5 . and we can subtract 2x from both sides . the left-hand side becomes negative y is equal to 2x plus -- or is equal to negative 2x plus 2.5 . now let 's multiply or divide both sides by negative 1 . and you get y is equal to positive 2x minus 2.5 . and let 's try to graph this , and you already might notice something interesting about these two equations . you try to graph this , the y-intercept is at negative 2.5 , right there . the slope is 2 . so it 's going to be this exact same line . and you saw that algebraically . i did n't have to graph it . these two lines have the exact same equation when you put them in slope-intercept form . that 's the first equation . that 's the second equation . so what this 0 equals 0 is telling us is actually that these are the same line . that these actually have an infinite number of solutions . any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . these are the same line . | we can say , hey , look , the negative 4x and the positive 4x should cancel out , or they will cancel out . so let 's add these two equations . let 's add the left side to the left side , the right side to the right side , and we can do that because these two things are equal . | how is zero the same as two point five ? |
we 're told to solve and graph the solution for the system of equations right here . and the first thing that jumps out at me , is that we might be able to eliminate one of the variables . and if we just focus on the x , we have a 4x here and we have a 2x right here . if we were to just add them right now , we would get a 6x . so that would n't eliminate it . but if we can multiply this 2x by negative 2 , it 'll become a negative 4x , and then when you add it , they would cancel out . so let 's multiply this equation , this second equation , by negative 2 . so i 'm going to multiply both sides of this equation by negative 2 . and the whole motivation is so that this 2x becomes a negative 4x . and , of course , i ca n't just multiply only the 2x . anything i do to the left-hand side of the equation i have to do to every term , and i have to do to both sides of the equation . so the second equation becomes negative 4x -- that 's negative 2 times 2x -- plus -- we have negative 2 times negative y -- which is plus 2y is equal to 2.5 times negative 2 , is equal to negative 5 . i just rewrote the second equation , multiplying both sides by negative 2 . now , this top equation -- i 'll write it on the bottom now -- we have 4x minus 2y is equal to positive 5 . and now we can eliminate it . we can say , hey , look , the negative 4x and the positive 4x should cancel out , or they will cancel out . so let 's add these two equations . let 's add the left side to the left side , the right side to the right side , and we can do that because these two things are equal . we 're doing the same thing to both sides of the equation . so what do we get ? if we take our negative 4x plus our 4x , well , those cancel out . so you 're left with nothing . maybe i could write a 0 there . 0x if you want . and then you have your plus 2y and your negative 2y . those also cancel out . so you 're also left with 0y . and then that equals negative 5 plus 5 is equal to 0 . so this just simplifies to 0 equals 0 , which is true , but it 's kind of bizarre . we had all these x 's and y 's . everything canceled out . so let 's explore this a little bit more . let 's graph it and see what this 0 equals 0 is telling us when we try to solve this system of equations . so let me graph this top guy . i 'll do it in blue . so right now it 's in standard form . let 's put it in slope-intercept form . so we have 4x minus 2y is equal to 5 . let 's subtract 4x from both sides . i want the x terms on the right-hand side . so then i 'm left with negative 2y is equal to negative 4x plus 5 . now we can divide both sides by negative 2 . and we are left with y is equal to positive 2x , right , that 's positive 2x , minus 2.5 . so let 's graph that . the y-intercept is negative 2.5 . so negative 2.5 right there , and then it has a slope of 2 . so if we move up 1 , if we move up in the x-direction , if we move to the right 1 in the positive x-direction , we will move up 2 . so 1 , 2 . right there . and if we were to do it again , we move up 1 , 2 . just like that . so the line 's going to look something like this . i 'll try my best to draw a straight line . this is the hardest part about a lot of these problems . there you go . so that 's the top equation . now , let me draw the bottom equation . let me draw and i 'll do it in this green color . so this bottom equation was 2x minus y is equal to 2.5 . and we can subtract 2x from both sides . the left-hand side becomes negative y is equal to 2x plus -- or is equal to negative 2x plus 2.5 . now let 's multiply or divide both sides by negative 1 . and you get y is equal to positive 2x minus 2.5 . and let 's try to graph this , and you already might notice something interesting about these two equations . you try to graph this , the y-intercept is at negative 2.5 , right there . the slope is 2 . so it 's going to be this exact same line . and you saw that algebraically . i did n't have to graph it . these two lines have the exact same equation when you put them in slope-intercept form . that 's the first equation . that 's the second equation . so what this 0 equals 0 is telling us is actually that these are the same line . that these actually have an infinite number of solutions . any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . these are the same line . | any point on this line , which is both of those lines , will satisfy both of these equations . you give me an arbitrary y , solve for x in the top equation , that x and y will also satisfy the bottom equation . so this actually has an infinite number of solutions . | what happens if you get one equation like 'x + 3y - 4 = 0 ' ? |
- for every work of art on paper that survives today intact or relatively intact , it 's hard to estimate , but there are probably many , many more works on paper that did n't survive . our department cares for the collections of drawings , manuscripts , and photographs . i personally am a conservator of photographs . the conservation of drawings , manuscripts , and photographs is grouped together because they all have physically similar types of objects . these three collections and the materials that compose them share a common vulnerability to the environment . they are all readily reactive to changes in relative humidity , and tend to be light sensitive . this is a gelatin silver print by august sander dating from 1928 . when it came into our collection , there were numerous losses scattered throughout the image . the gelatin binder apparently had been exposed to light over prolonged periods of time , possibly on display . when this happens , gelatin will first begin to lift away from its paper support and then flake away , resulting in losses . we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . you 'll find that the galleries in the museum are lit significantly low in the drawings , manuscripts , and photo galleries , significantly lower than the other areas , such as sculpture and painting . and that is also to limit their exposure to light . these are two german illuminated manuscripts from the 15th century . they provide an interesting comparison . originally both of these albums had clasps which held the album tightly together . at some point in its life the clasps were lost on this album , which opened it up to the environment . alternate changes in relative humidity caused the individual sheets of parchment to expand and contract . and as a result , the album we have today is wedge shaped because of all the bulges and cockling in each individual sheet of parchment in the manuscript . this red chalk drawing by guilio romano entitled `` the sacrifice of isaac '' from the early 16th century came into our collection a victim of insect infestation . there were numerous small worm holes scattered throughout the paper support . a restorer had well-meaningly placed small squares of paper in behind each worm hole , which had resulted in numerous bulges throughout the paper . our drawings conservator , nancy yocco , was able , with controlled applications of moisture , to remove the drawing from its collectors mount and then remove each individual patch repair behind the worm holes . with those gone , she was able then to fill in the losses in each worm hole with paper pulp . once that was done , that paper was toned to be compatible with the color of the surrounding areas in the image . particular pollutants , and i 'm talking about dirt , airborne grime , and dust , can also have harmful effects of works of art on paper . an example of an artwork which had a problem with airborne dust and dirt is david hockney 's `` pairblossom highway . '' this is a collage composed of about 750 snapshot chromogenic prints assembled on one panel . and this particular adhesive that he used was very stable , but it 's a tacky adhesive . airborne dust has found its way into contact with that tacky adhesive which remains on the surface . now , when `` pearblossom highway '' came into the museum , there were several small , black patches scattered over the surface of the collage . we used special erasers to remove this tacky adhesive from the collage . this was a fairly long treatment which our entire department took part in . once all those areas were gone , the whole collage read better overall . and when you looked at the collage , your eye did n't go straight to these small black areas of discoloration . | i personally am a conservator of photographs . the conservation of drawings , manuscripts , and photographs is grouped together because they all have physically similar types of objects . these three collections and the materials that compose them share a common vulnerability to the environment . | how is paper conservation different from photograph conservation ? |
- for every work of art on paper that survives today intact or relatively intact , it 's hard to estimate , but there are probably many , many more works on paper that did n't survive . our department cares for the collections of drawings , manuscripts , and photographs . i personally am a conservator of photographs . the conservation of drawings , manuscripts , and photographs is grouped together because they all have physically similar types of objects . these three collections and the materials that compose them share a common vulnerability to the environment . they are all readily reactive to changes in relative humidity , and tend to be light sensitive . this is a gelatin silver print by august sander dating from 1928 . when it came into our collection , there were numerous losses scattered throughout the image . the gelatin binder apparently had been exposed to light over prolonged periods of time , possibly on display . when this happens , gelatin will first begin to lift away from its paper support and then flake away , resulting in losses . we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . you 'll find that the galleries in the museum are lit significantly low in the drawings , manuscripts , and photo galleries , significantly lower than the other areas , such as sculpture and painting . and that is also to limit their exposure to light . these are two german illuminated manuscripts from the 15th century . they provide an interesting comparison . originally both of these albums had clasps which held the album tightly together . at some point in its life the clasps were lost on this album , which opened it up to the environment . alternate changes in relative humidity caused the individual sheets of parchment to expand and contract . and as a result , the album we have today is wedge shaped because of all the bulges and cockling in each individual sheet of parchment in the manuscript . this red chalk drawing by guilio romano entitled `` the sacrifice of isaac '' from the early 16th century came into our collection a victim of insect infestation . there were numerous small worm holes scattered throughout the paper support . a restorer had well-meaningly placed small squares of paper in behind each worm hole , which had resulted in numerous bulges throughout the paper . our drawings conservator , nancy yocco , was able , with controlled applications of moisture , to remove the drawing from its collectors mount and then remove each individual patch repair behind the worm holes . with those gone , she was able then to fill in the losses in each worm hole with paper pulp . once that was done , that paper was toned to be compatible with the color of the surrounding areas in the image . particular pollutants , and i 'm talking about dirt , airborne grime , and dust , can also have harmful effects of works of art on paper . an example of an artwork which had a problem with airborne dust and dirt is david hockney 's `` pairblossom highway . '' this is a collage composed of about 750 snapshot chromogenic prints assembled on one panel . and this particular adhesive that he used was very stable , but it 's a tacky adhesive . airborne dust has found its way into contact with that tacky adhesive which remains on the surface . now , when `` pearblossom highway '' came into the museum , there were several small , black patches scattered over the surface of the collage . we used special erasers to remove this tacky adhesive from the collage . this was a fairly long treatment which our entire department took part in . once all those areas were gone , the whole collage read better overall . and when you looked at the collage , your eye did n't go straight to these small black areas of discoloration . | when this happens , gelatin will first begin to lift away from its paper support and then flake away , resulting in losses . we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . | how does one become art conservationist ? |
- for every work of art on paper that survives today intact or relatively intact , it 's hard to estimate , but there are probably many , many more works on paper that did n't survive . our department cares for the collections of drawings , manuscripts , and photographs . i personally am a conservator of photographs . the conservation of drawings , manuscripts , and photographs is grouped together because they all have physically similar types of objects . these three collections and the materials that compose them share a common vulnerability to the environment . they are all readily reactive to changes in relative humidity , and tend to be light sensitive . this is a gelatin silver print by august sander dating from 1928 . when it came into our collection , there were numerous losses scattered throughout the image . the gelatin binder apparently had been exposed to light over prolonged periods of time , possibly on display . when this happens , gelatin will first begin to lift away from its paper support and then flake away , resulting in losses . we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . you 'll find that the galleries in the museum are lit significantly low in the drawings , manuscripts , and photo galleries , significantly lower than the other areas , such as sculpture and painting . and that is also to limit their exposure to light . these are two german illuminated manuscripts from the 15th century . they provide an interesting comparison . originally both of these albums had clasps which held the album tightly together . at some point in its life the clasps were lost on this album , which opened it up to the environment . alternate changes in relative humidity caused the individual sheets of parchment to expand and contract . and as a result , the album we have today is wedge shaped because of all the bulges and cockling in each individual sheet of parchment in the manuscript . this red chalk drawing by guilio romano entitled `` the sacrifice of isaac '' from the early 16th century came into our collection a victim of insect infestation . there were numerous small worm holes scattered throughout the paper support . a restorer had well-meaningly placed small squares of paper in behind each worm hole , which had resulted in numerous bulges throughout the paper . our drawings conservator , nancy yocco , was able , with controlled applications of moisture , to remove the drawing from its collectors mount and then remove each individual patch repair behind the worm holes . with those gone , she was able then to fill in the losses in each worm hole with paper pulp . once that was done , that paper was toned to be compatible with the color of the surrounding areas in the image . particular pollutants , and i 'm talking about dirt , airborne grime , and dust , can also have harmful effects of works of art on paper . an example of an artwork which had a problem with airborne dust and dirt is david hockney 's `` pairblossom highway . '' this is a collage composed of about 750 snapshot chromogenic prints assembled on one panel . and this particular adhesive that he used was very stable , but it 's a tacky adhesive . airborne dust has found its way into contact with that tacky adhesive which remains on the surface . now , when `` pearblossom highway '' came into the museum , there were several small , black patches scattered over the surface of the collage . we used special erasers to remove this tacky adhesive from the collage . this was a fairly long treatment which our entire department took part in . once all those areas were gone , the whole collage read better overall . and when you looked at the collage , your eye did n't go straight to these small black areas of discoloration . | this red chalk drawing by guilio romano entitled `` the sacrifice of isaac '' from the early 16th century came into our collection a victim of insect infestation . there were numerous small worm holes scattered throughout the paper support . a restorer had well-meaningly placed small squares of paper in behind each worm hole , which had resulted in numerous bulges throughout the paper . our drawings conservator , nancy yocco , was able , with controlled applications of moisture , to remove the drawing from its collectors mount and then remove each individual patch repair behind the worm holes . | is there a certain type of light that slows down or prevents paper/photograph degredation ? |
- for every work of art on paper that survives today intact or relatively intact , it 's hard to estimate , but there are probably many , many more works on paper that did n't survive . our department cares for the collections of drawings , manuscripts , and photographs . i personally am a conservator of photographs . the conservation of drawings , manuscripts , and photographs is grouped together because they all have physically similar types of objects . these three collections and the materials that compose them share a common vulnerability to the environment . they are all readily reactive to changes in relative humidity , and tend to be light sensitive . this is a gelatin silver print by august sander dating from 1928 . when it came into our collection , there were numerous losses scattered throughout the image . the gelatin binder apparently had been exposed to light over prolonged periods of time , possibly on display . when this happens , gelatin will first begin to lift away from its paper support and then flake away , resulting in losses . we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . you 'll find that the galleries in the museum are lit significantly low in the drawings , manuscripts , and photo galleries , significantly lower than the other areas , such as sculpture and painting . and that is also to limit their exposure to light . these are two german illuminated manuscripts from the 15th century . they provide an interesting comparison . originally both of these albums had clasps which held the album tightly together . at some point in its life the clasps were lost on this album , which opened it up to the environment . alternate changes in relative humidity caused the individual sheets of parchment to expand and contract . and as a result , the album we have today is wedge shaped because of all the bulges and cockling in each individual sheet of parchment in the manuscript . this red chalk drawing by guilio romano entitled `` the sacrifice of isaac '' from the early 16th century came into our collection a victim of insect infestation . there were numerous small worm holes scattered throughout the paper support . a restorer had well-meaningly placed small squares of paper in behind each worm hole , which had resulted in numerous bulges throughout the paper . our drawings conservator , nancy yocco , was able , with controlled applications of moisture , to remove the drawing from its collectors mount and then remove each individual patch repair behind the worm holes . with those gone , she was able then to fill in the losses in each worm hole with paper pulp . once that was done , that paper was toned to be compatible with the color of the surrounding areas in the image . particular pollutants , and i 'm talking about dirt , airborne grime , and dust , can also have harmful effects of works of art on paper . an example of an artwork which had a problem with airborne dust and dirt is david hockney 's `` pairblossom highway . '' this is a collage composed of about 750 snapshot chromogenic prints assembled on one panel . and this particular adhesive that he used was very stable , but it 's a tacky adhesive . airborne dust has found its way into contact with that tacky adhesive which remains on the surface . now , when `` pearblossom highway '' came into the museum , there were several small , black patches scattered over the surface of the collage . we used special erasers to remove this tacky adhesive from the collage . this was a fairly long treatment which our entire department took part in . once all those areas were gone , the whole collage read better overall . and when you looked at the collage , your eye did n't go straight to these small black areas of discoloration . | we change our displays of works of art on paper every 12 weeks . we do this to limit their exposure to light . you 'll find that the galleries in the museum are lit significantly low in the drawings , manuscripts , and photo galleries , significantly lower than the other areas , such as sculpture and painting . | the light in the exhibit they showed seems a bit yellowish , is that a factor ? |
: the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . the number of cars that will be shipped to vietnam during the next t months is modeled by the function v of t is equal to 2t squared . which country had received more cars from the cozy car company after 5 months , or will have received after 5 months ? let 's see how much japan is going to receive after 5 months . t is in months , so j of 5 is going to be equal to 2 to the 5th power , which is equal to 2 times 2 times 2 times 2 times 2 , and let 's see , 2 times just 4 , 8 , 16 , 32 . japan will have received 32 cars , and vietnam , so v of 5 is going to be 2 times 5 squared , which is going to be 2 times 25 , which is equal to 50 . based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? once again , let 's try this out . j of 7 is equal to 2 to the 7th power . let 's see . 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . we see that the exponential function , notice where you have the t as the exponent , that although it might start off a little bit slower than this , what 's essentially a quadratic function when you have something squared , it starts off slow . after 5 months , you would have shipped fewer cars than using the quadratic model right over here . but then , it more than catches up , and it starts to increase at a faster and faster rate , and even by 7 months , it 's able to pass up the quadratic function . which country will have received more cars from the cozy car company ... will the country which received more cars from the cozy car company after 7 months continue to receive more cars than the other country in future months ? yeah , absolutely . once the exponential function passes up the quadratic function , it just goes faster . it just keeps increasing at a faster and faster rate . you could see that if we wanted to compare 8 months , so j of 8 , this is the exponential function , this would be 2 to the 8th power , which would be this times 2 , they 'd get 256 cars , and v of 8 , v of 8 is going to be 2 times 8 squared , which is 2 times 64 , which is 128 . notice now we would have shipped twice as much to japan as vietnam , which is n't what the case right over here . we shipped more to japan than vietnam but not twice as much . we could keep going . we could , if you want , you could go to j of 9. j of 9 is 2 to the 9th power , which is going to be 256 times 2 or 512 cars , while v of 9 , v of 9 is going to be 2 times 9 squared , which is 2 times 81 , which is 162 , so now it 's more , way more than double , actually more than triple . so you see that once you get past those initial few months , the exponential function is increasing at a much , much , much faster rate . we could actually visualize that . let 's actually get out a graphing calculator to visualize these 2 things to see how that is happening . let 's graph it . the first one , let me graph the exponential , so 2 to the , well , i 'll just say x power . we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . let 's say 2 times x , 2 times x squared . now let me set the range . let me set the range here . let 's see . let 's say x starts at 0 , and then let 's say it goes up to 10 . let 's say it goes up to 10 . the x-scale could be 1 . x-scale could be 1 . now y 's minimum , let 's say we 'll start at 0 , and then y-max , let 's say , let 's go to 1,000 . let 's go to 1,000 , and let 's make the y-scale 100 , 100 , and now i think we 're ready to graph . let 's graph this . let 's see what happens . it 's munching on things . that , right over there , that 's the exponential , and then there , you see right over there , you have the quadratic . actually , let me zoom in a little bit on this so that we can see where they pass ... or actually , let me zoom in a little bit on this . i 'll do it with a box so that we can really see , we can see where they , or attempt to see where they pass each other up . i 'm going to start there . i 'm going to make my box , let 's see , go ... whoops . it 's weird using a calculator on a computer like this . but you see , you definitely see , even what we 've already graphed , that the exponential really just starts to shoot up while the quadratic is just going ... well , it 's still increasing at a decent pace but nowhere near as fast , and the difference is becoming more and more pronounced as time increases . let me just make sure that 's as low as that , and let 's graph over in this range right over here . let 's see . that , right over there , that 's the exponential function . that 's 2 to the t power . then that right over there is the quadratic . you see , you definitely see ... actually let me ... you definitely see that earlier on , the quadratic has higher values , and you see that right over here , after 5 months , we ship more cars to vietnam . but then the exponential passes it up and then just keeps shooting faster at an ever increasing pace . | based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? | how is vietnam not exponential growth ? |
: the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . the number of cars that will be shipped to vietnam during the next t months is modeled by the function v of t is equal to 2t squared . which country had received more cars from the cozy car company after 5 months , or will have received after 5 months ? let 's see how much japan is going to receive after 5 months . t is in months , so j of 5 is going to be equal to 2 to the 5th power , which is equal to 2 times 2 times 2 times 2 times 2 , and let 's see , 2 times just 4 , 8 , 16 , 32 . japan will have received 32 cars , and vietnam , so v of 5 is going to be 2 times 5 squared , which is going to be 2 times 25 , which is equal to 50 . based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? once again , let 's try this out . j of 7 is equal to 2 to the 7th power . let 's see . 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . we see that the exponential function , notice where you have the t as the exponent , that although it might start off a little bit slower than this , what 's essentially a quadratic function when you have something squared , it starts off slow . after 5 months , you would have shipped fewer cars than using the quadratic model right over here . but then , it more than catches up , and it starts to increase at a faster and faster rate , and even by 7 months , it 's able to pass up the quadratic function . which country will have received more cars from the cozy car company ... will the country which received more cars from the cozy car company after 7 months continue to receive more cars than the other country in future months ? yeah , absolutely . once the exponential function passes up the quadratic function , it just goes faster . it just keeps increasing at a faster and faster rate . you could see that if we wanted to compare 8 months , so j of 8 , this is the exponential function , this would be 2 to the 8th power , which would be this times 2 , they 'd get 256 cars , and v of 8 , v of 8 is going to be 2 times 8 squared , which is 2 times 64 , which is 128 . notice now we would have shipped twice as much to japan as vietnam , which is n't what the case right over here . we shipped more to japan than vietnam but not twice as much . we could keep going . we could , if you want , you could go to j of 9. j of 9 is 2 to the 9th power , which is going to be 256 times 2 or 512 cars , while v of 9 , v of 9 is going to be 2 times 9 squared , which is 2 times 81 , which is 162 , so now it 's more , way more than double , actually more than triple . so you see that once you get past those initial few months , the exponential function is increasing at a much , much , much faster rate . we could actually visualize that . let 's actually get out a graphing calculator to visualize these 2 things to see how that is happening . let 's graph it . the first one , let me graph the exponential , so 2 to the , well , i 'll just say x power . we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . let 's say 2 times x , 2 times x squared . now let me set the range . let me set the range here . let 's see . let 's say x starts at 0 , and then let 's say it goes up to 10 . let 's say it goes up to 10 . the x-scale could be 1 . x-scale could be 1 . now y 's minimum , let 's say we 'll start at 0 , and then y-max , let 's say , let 's go to 1,000 . let 's go to 1,000 , and let 's make the y-scale 100 , 100 , and now i think we 're ready to graph . let 's graph this . let 's see what happens . it 's munching on things . that , right over there , that 's the exponential , and then there , you see right over there , you have the quadratic . actually , let me zoom in a little bit on this so that we can see where they pass ... or actually , let me zoom in a little bit on this . i 'll do it with a box so that we can really see , we can see where they , or attempt to see where they pass each other up . i 'm going to start there . i 'm going to make my box , let 's see , go ... whoops . it 's weird using a calculator on a computer like this . but you see , you definitely see , even what we 've already graphed , that the exponential really just starts to shoot up while the quadratic is just going ... well , it 's still increasing at a decent pace but nowhere near as fast , and the difference is becoming more and more pronounced as time increases . let me just make sure that 's as low as that , and let 's graph over in this range right over here . let 's see . that , right over there , that 's the exponential function . that 's 2 to the t power . then that right over there is the quadratic . you see , you definitely see ... actually let me ... you definitely see that earlier on , the quadratic has higher values , and you see that right over here , after 5 months , we ship more cars to vietnam . but then the exponential passes it up and then just keeps shooting faster at an ever increasing pace . | 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . | how could we have proved that japan will have received more cars after the 7th month ? |
: the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . the number of cars that will be shipped to vietnam during the next t months is modeled by the function v of t is equal to 2t squared . which country had received more cars from the cozy car company after 5 months , or will have received after 5 months ? let 's see how much japan is going to receive after 5 months . t is in months , so j of 5 is going to be equal to 2 to the 5th power , which is equal to 2 times 2 times 2 times 2 times 2 , and let 's see , 2 times just 4 , 8 , 16 , 32 . japan will have received 32 cars , and vietnam , so v of 5 is going to be 2 times 5 squared , which is going to be 2 times 25 , which is equal to 50 . based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? once again , let 's try this out . j of 7 is equal to 2 to the 7th power . let 's see . 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . we see that the exponential function , notice where you have the t as the exponent , that although it might start off a little bit slower than this , what 's essentially a quadratic function when you have something squared , it starts off slow . after 5 months , you would have shipped fewer cars than using the quadratic model right over here . but then , it more than catches up , and it starts to increase at a faster and faster rate , and even by 7 months , it 's able to pass up the quadratic function . which country will have received more cars from the cozy car company ... will the country which received more cars from the cozy car company after 7 months continue to receive more cars than the other country in future months ? yeah , absolutely . once the exponential function passes up the quadratic function , it just goes faster . it just keeps increasing at a faster and faster rate . you could see that if we wanted to compare 8 months , so j of 8 , this is the exponential function , this would be 2 to the 8th power , which would be this times 2 , they 'd get 256 cars , and v of 8 , v of 8 is going to be 2 times 8 squared , which is 2 times 64 , which is 128 . notice now we would have shipped twice as much to japan as vietnam , which is n't what the case right over here . we shipped more to japan than vietnam but not twice as much . we could keep going . we could , if you want , you could go to j of 9. j of 9 is 2 to the 9th power , which is going to be 256 times 2 or 512 cars , while v of 9 , v of 9 is going to be 2 times 9 squared , which is 2 times 81 , which is 162 , so now it 's more , way more than double , actually more than triple . so you see that once you get past those initial few months , the exponential function is increasing at a much , much , much faster rate . we could actually visualize that . let 's actually get out a graphing calculator to visualize these 2 things to see how that is happening . let 's graph it . the first one , let me graph the exponential , so 2 to the , well , i 'll just say x power . we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . let 's say 2 times x , 2 times x squared . now let me set the range . let me set the range here . let 's see . let 's say x starts at 0 , and then let 's say it goes up to 10 . let 's say it goes up to 10 . the x-scale could be 1 . x-scale could be 1 . now y 's minimum , let 's say we 'll start at 0 , and then y-max , let 's say , let 's go to 1,000 . let 's go to 1,000 , and let 's make the y-scale 100 , 100 , and now i think we 're ready to graph . let 's graph this . let 's see what happens . it 's munching on things . that , right over there , that 's the exponential , and then there , you see right over there , you have the quadratic . actually , let me zoom in a little bit on this so that we can see where they pass ... or actually , let me zoom in a little bit on this . i 'll do it with a box so that we can really see , we can see where they , or attempt to see where they pass each other up . i 'm going to start there . i 'm going to make my box , let 's see , go ... whoops . it 's weird using a calculator on a computer like this . but you see , you definitely see , even what we 've already graphed , that the exponential really just starts to shoot up while the quadratic is just going ... well , it 's still increasing at a decent pace but nowhere near as fast , and the difference is becoming more and more pronounced as time increases . let me just make sure that 's as low as that , and let 's graph over in this range right over here . let 's see . that , right over there , that 's the exponential function . that 's 2 to the t power . then that right over there is the quadratic . you see , you definitely see ... actually let me ... you definitely see that earlier on , the quadratic has higher values , and you see that right over here , after 5 months , we ship more cars to vietnam . but then the exponential passes it up and then just keeps shooting faster at an ever increasing pace . | we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . | how does the quadratic equation have a linear graphing even though it has an exponent ? |
: the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . the number of cars that will be shipped to vietnam during the next t months is modeled by the function v of t is equal to 2t squared . which country had received more cars from the cozy car company after 5 months , or will have received after 5 months ? let 's see how much japan is going to receive after 5 months . t is in months , so j of 5 is going to be equal to 2 to the 5th power , which is equal to 2 times 2 times 2 times 2 times 2 , and let 's see , 2 times just 4 , 8 , 16 , 32 . japan will have received 32 cars , and vietnam , so v of 5 is going to be 2 times 5 squared , which is going to be 2 times 25 , which is equal to 50 . based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? once again , let 's try this out . j of 7 is equal to 2 to the 7th power . let 's see . 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . we see that the exponential function , notice where you have the t as the exponent , that although it might start off a little bit slower than this , what 's essentially a quadratic function when you have something squared , it starts off slow . after 5 months , you would have shipped fewer cars than using the quadratic model right over here . but then , it more than catches up , and it starts to increase at a faster and faster rate , and even by 7 months , it 's able to pass up the quadratic function . which country will have received more cars from the cozy car company ... will the country which received more cars from the cozy car company after 7 months continue to receive more cars than the other country in future months ? yeah , absolutely . once the exponential function passes up the quadratic function , it just goes faster . it just keeps increasing at a faster and faster rate . you could see that if we wanted to compare 8 months , so j of 8 , this is the exponential function , this would be 2 to the 8th power , which would be this times 2 , they 'd get 256 cars , and v of 8 , v of 8 is going to be 2 times 8 squared , which is 2 times 64 , which is 128 . notice now we would have shipped twice as much to japan as vietnam , which is n't what the case right over here . we shipped more to japan than vietnam but not twice as much . we could keep going . we could , if you want , you could go to j of 9. j of 9 is 2 to the 9th power , which is going to be 256 times 2 or 512 cars , while v of 9 , v of 9 is going to be 2 times 9 squared , which is 2 times 81 , which is 162 , so now it 's more , way more than double , actually more than triple . so you see that once you get past those initial few months , the exponential function is increasing at a much , much , much faster rate . we could actually visualize that . let 's actually get out a graphing calculator to visualize these 2 things to see how that is happening . let 's graph it . the first one , let me graph the exponential , so 2 to the , well , i 'll just say x power . we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . let 's say 2 times x , 2 times x squared . now let me set the range . let me set the range here . let 's see . let 's say x starts at 0 , and then let 's say it goes up to 10 . let 's say it goes up to 10 . the x-scale could be 1 . x-scale could be 1 . now y 's minimum , let 's say we 'll start at 0 , and then y-max , let 's say , let 's go to 1,000 . let 's go to 1,000 , and let 's make the y-scale 100 , 100 , and now i think we 're ready to graph . let 's graph this . let 's see what happens . it 's munching on things . that , right over there , that 's the exponential , and then there , you see right over there , you have the quadratic . actually , let me zoom in a little bit on this so that we can see where they pass ... or actually , let me zoom in a little bit on this . i 'll do it with a box so that we can really see , we can see where they , or attempt to see where they pass each other up . i 'm going to start there . i 'm going to make my box , let 's see , go ... whoops . it 's weird using a calculator on a computer like this . but you see , you definitely see , even what we 've already graphed , that the exponential really just starts to shoot up while the quadratic is just going ... well , it 's still increasing at a decent pace but nowhere near as fast , and the difference is becoming more and more pronounced as time increases . let me just make sure that 's as low as that , and let 's graph over in this range right over here . let 's see . that , right over there , that 's the exponential function . that 's 2 to the t power . then that right over there is the quadratic . you see , you definitely see ... actually let me ... you definitely see that earlier on , the quadratic has higher values , and you see that right over here , after 5 months , we ship more cars to vietnam . but then the exponential passes it up and then just keeps shooting faster at an ever increasing pace . | : the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . | does the equation form a parabola ? |
: the cozy car company ships some of their new cars to japan and vietnam . the number of cars that will be shipped to japan during the next t months is modeled by the function j of t is equal to 2 to the tth power . the number of cars that will be shipped to vietnam during the next t months is modeled by the function v of t is equal to 2t squared . which country had received more cars from the cozy car company after 5 months , or will have received after 5 months ? let 's see how much japan is going to receive after 5 months . t is in months , so j of 5 is going to be equal to 2 to the 5th power , which is equal to 2 times 2 times 2 times 2 times 2 , and let 's see , 2 times just 4 , 8 , 16 , 32 . japan will have received 32 cars , and vietnam , so v of 5 is going to be 2 times 5 squared , which is going to be 2 times 25 , which is equal to 50 . based on these 2 models for how much they 're going to receive after t months , after 5 months , vietnam is going to receive , vietnam is going to receive more cars . i guess the answer to that is vietnam . vietnam will have received more cars after 5 months . which country had received more cars from the cozy car company , or will have received more cars after 7 months ? once again , let 's try this out . j of 7 is equal to 2 to the 7th power . let 's see . 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . we see that the exponential function , notice where you have the t as the exponent , that although it might start off a little bit slower than this , what 's essentially a quadratic function when you have something squared , it starts off slow . after 5 months , you would have shipped fewer cars than using the quadratic model right over here . but then , it more than catches up , and it starts to increase at a faster and faster rate , and even by 7 months , it 's able to pass up the quadratic function . which country will have received more cars from the cozy car company ... will the country which received more cars from the cozy car company after 7 months continue to receive more cars than the other country in future months ? yeah , absolutely . once the exponential function passes up the quadratic function , it just goes faster . it just keeps increasing at a faster and faster rate . you could see that if we wanted to compare 8 months , so j of 8 , this is the exponential function , this would be 2 to the 8th power , which would be this times 2 , they 'd get 256 cars , and v of 8 , v of 8 is going to be 2 times 8 squared , which is 2 times 64 , which is 128 . notice now we would have shipped twice as much to japan as vietnam , which is n't what the case right over here . we shipped more to japan than vietnam but not twice as much . we could keep going . we could , if you want , you could go to j of 9. j of 9 is 2 to the 9th power , which is going to be 256 times 2 or 512 cars , while v of 9 , v of 9 is going to be 2 times 9 squared , which is 2 times 81 , which is 162 , so now it 's more , way more than double , actually more than triple . so you see that once you get past those initial few months , the exponential function is increasing at a much , much , much faster rate . we could actually visualize that . let 's actually get out a graphing calculator to visualize these 2 things to see how that is happening . let 's graph it . the first one , let me graph the exponential , so 2 to the , well , i 'll just say x power . we 'll say x is our independent variable here , so 2 to the x power . then let 's do the quadratic one . this is y of 2 , although it will be v of 2 . let 's say 2 times x , 2 times x squared . now let me set the range . let me set the range here . let 's see . let 's say x starts at 0 , and then let 's say it goes up to 10 . let 's say it goes up to 10 . the x-scale could be 1 . x-scale could be 1 . now y 's minimum , let 's say we 'll start at 0 , and then y-max , let 's say , let 's go to 1,000 . let 's go to 1,000 , and let 's make the y-scale 100 , 100 , and now i think we 're ready to graph . let 's graph this . let 's see what happens . it 's munching on things . that , right over there , that 's the exponential , and then there , you see right over there , you have the quadratic . actually , let me zoom in a little bit on this so that we can see where they pass ... or actually , let me zoom in a little bit on this . i 'll do it with a box so that we can really see , we can see where they , or attempt to see where they pass each other up . i 'm going to start there . i 'm going to make my box , let 's see , go ... whoops . it 's weird using a calculator on a computer like this . but you see , you definitely see , even what we 've already graphed , that the exponential really just starts to shoot up while the quadratic is just going ... well , it 's still increasing at a decent pace but nowhere near as fast , and the difference is becoming more and more pronounced as time increases . let me just make sure that 's as low as that , and let 's graph over in this range right over here . let 's see . that , right over there , that 's the exponential function . that 's 2 to the t power . then that right over there is the quadratic . you see , you definitely see ... actually let me ... you definitely see that earlier on , the quadratic has higher values , and you see that right over here , after 5 months , we ship more cars to vietnam . but then the exponential passes it up and then just keeps shooting faster at an ever increasing pace . | 2 to the 6th is going to be 32 times ... we can read this as 2 to the 5th times 2 times 2 , which is going to be equal to , this is going to be equal to 32 times 4 , which is 128 cars after 7 months will have gone to japan , and to vietnam , v of 7 is going to be equal to 2 times 7 squared , so that 's equal to 2 times 49 , which is equal to 98 cars . after 7 months , japan would have received more cars , so japan , japan will have received more cars after 7 months . this is interesting . | why the answer is not the number of the total number of cars japan or vietnam received ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | how the nodes can boast the signal of ions ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | is myelin sheath same as schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | what disease occurs when the myelin sheath is damaged or missing ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | when the action potential is initiated at the axon hillock , what prevents the inflow of ions from migrating ( diffusing ) back towards the cell body/dendrites ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . | what other organs are near the brain , and what type of tissue makes up the brain ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | is myelin sheath same as schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | how do positively charged ions carry a signal ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | would n't the signal be diluted at the nodes of ranvier when it just gets flooded with more ions ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . | how does the transmission goes in the right direction ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | sal explains that we have gaps in our myelin sheath so that we could `` boost '' the signal with voltage gated channels , so if we intake extra calcium , would it be that this would boost the signal even more ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . | how are the k= that are lost during the stimulation re-supplemented ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | what is exactly a myelin ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . | and why ca n't voltage-gated channels be placed on the surface of myelin ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | is myelin sheath same as schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? | electrotonic spread happens in the axon , right ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . | so , what keeps the signal from going back into the receptor instead of going on to the terminal , especially when the signal receives the boost ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | during a boosting of action potential ( in nodes of ranvier ) , how come that there 's always an influx of sodium ions when there 's too many na ions inside the cell ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | is n't it that the natural flow of ions should be from a higher concentration to lower concentration gradient ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? | do neurons have any calcium channels anywhere else besides the end of the axon ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . | is there a name for the voltage gated channels in the nodes of ranvier ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . | what is the mv needed to stimulate the voltage gated ions at the node or ranvier ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . | one last question , are there any ion channels and na/k pumps under the schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | does an action potential travel along an axon or does it stimulate the production of a new action potential in the membrane ahead of it ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . | if there is no stimulus , does the saltatory conduction happens ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . | what comprises the extracellular space of neurons ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . | why these nodes are called as nodes of ranvier ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . | i am still confused on how the signal gets boosted at nodes of ranvier ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . | what does high resistance mean ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | why is mostly sodium and potassium ions affect the action potential ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . | why do we need high resistance of myelin sheaths ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . | is n't the phospholipid layer already a good insulator ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | can positive ions only go inside the neuron ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . | why are the nodes called nodes of ranvier ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | sal drew the sodium ions entering the the cell itself , but the cells atucally enter and travel along the membrane ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . | dont the pumps for the potassium pump potassium out when there 's alot of positive charge making the the sodium dicipate before it reaches the next sodium pump ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . | can anyone please explain to me how the current flows from dendrites to axon ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . | if some of our axons can be up to 1 meter , how does it fit in our head ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . | does the voltage required to fire the action potentials between the hillock and each individual node differ ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . | how long does it take for the signal to get from the soma to the terminal ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . | what 's special about the hillock beside being the `` convergent point '' of the graded signals ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | can an action potential be generated at some point before the hillock if two signals happen to meet there and pass the threshold ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? | does this meant that people who have less nodes of ranvier and more myelin sheath have slower reflexes , since the more myelin sheath there is , the slower the signal carries ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . | do nodes of ranvier appear only in the pns , cns or both ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | is n't the purpose of the myelin sheath to prevent action potential from repeatedly generating along the whole axon thus slowing the signal down ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | if all the signals and informations transmit by stimulation of ion gates , and there is a uniform threshold to initiate the action potential , so what deferintiate one information from another ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . | at the node of ranvier , there are gated channels to boost the signals transmitted through axons , are those gated channels are always in pair ( 1 na + 1 k gated channels ) ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | how is action potential triggered at nerve endings where there is no nerve to give the signal to the receiving nerve ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . | does the saltatory conduction conserve energy for the axon ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . | are the voltage gated channels between the myelin the schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | is that because of the signal from one end of the nerve to the next does n't get amplified enough to have a strong signal ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . | for clarification , do stimuli cause the sodium to pass over the membrane for the first burst of energy ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | why will an action potential be stopped if the nodes of ranvier are wide apart ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . | are n't action potentials constant and will not be attenuated ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | so the nodes of ranvier essentially boost the signal using a method somewhat like pressure ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . | why is the voltage increase only a temporary bump as opposed to lasting longer ( as now the voltage of the inside is increasing due to the rush of sodium ) ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? | how can electrotonic conduction happen ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . | if the sodium potassium pump is random , why can you control your actions ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . | how large are the gaps between the schwann cells in real life ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . | how long are the schwann cells ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . | could n't the action/ electrical potential maintain itself while traveling down the axon without the myelin sheath via means of the voltage gated channels ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | i know there would be significantly more energy loss , but would n't the voltage gated channels dispersed across the axon make up for it , `` boosting '' the charge/potential all the way to the terminals ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . | what is the brain made out of ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . | how many nodes of ranvier per axon ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . | what diseases could occur if nodes of ranvier are not present ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . | why is it usually negative inside the cell ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . | why do we use ions instead of some sort of conductive fibre ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . | are n't chemicals too slow to allow the sort of fast paced thinking that neurons are capable of ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . | is there a disease that causes the nodes of ranvier not to be able to boost the signal , or is that just instant death ? |
now that we know how a signal can spread through a neuron , through an electrotonic potential and action potential and combinations of the two , let 's put it all together by looking again at the structure of a neuron , the anatomy of a neuron , and thinking about why it has that anatomy and how it all can work . so we 've already talked about the dendrites as being where the neuron can be stimulated from multiple inputs . if we 're in the brain , these dendrites might be near the terminal ends of axons of other neurons . if we 're some type of sensory cell , these dendrites could be stimulated by some type of sensory input . but let 's just say , for the sake of argument , they are stimulated in some way . and because they 're stimulated in some way , it allows positive ions to flood into the neuron from the outside . as we know , there 's a potential difference . it 's more negative inside of the neuron than outside of the neuron . and so if a channel gets opened up because of some stimulus , that would allow positive ions to flow in . and the primary positive ions we 've been talking about are the sodium ions . maybe this is some type of sodium gate that gets opened up because of this stimulus . so when that happens , you will have electrotonic spread . you will have an electrotonic potential being spread . so let 's say that we had a voltmeter right here on the axon hillock . it 's kind of the hill that leads to the axon right over here . so what you might see happening after some amount of time -- so let me draw . so let 's say this is our voltage in millivolts across the membrane -- our voltage difference , i should say . this is the passage of time . let 's say the stimulus happens at time 0 . but right at time 0 , we have n't really noticed it with our voltmeter . our voltage right across the membrane right over there is at that equilibrium , negative 70 millivolts . but after some small amount of time , this electrotonic potential has gotten to this point , because all of these positive charges are trying to get away from each other . it 's gotten to that point . and you might see a bump in the voltage -- in the voltage difference , i guess i should say . this thing might go up . so it might look something like that . now , that by itself might not be -- we might have gotten the voltage difference low enough , i guess we could say . or we might not have gotten the voltage inside of the cell positive enough in order to trigger the voltage-gated ion channels . and so maybe nothing happens . maybe this right over here , this is negative 55 millivolts . and so that 's what you have to get the voltage up to , the voltage difference up to , in order to trigger the ion channels right over there . so those are the sodium channels to get positive charge in . here 's the potassium channels to get the positive charge out . the axon hillock has a ton of these , because these are really there . once they get triggered , they can trigger an impulse that can then go down the entire axon , and maybe stimulate other things , maybe in the brain or whatever else this neuron might be connected to . so maybe that stimulus by itself did n't trigger it . but let 's say that there 's another stimulus that happens right at the same time , or around the same time . and that happens . and on its own , that might have caused a similar type of bump right over here . but when you add the two together and they 're happening at the same time , their combined bumps are enough to trigger an action potential in the hillock , or a series of action potentials in the hillock . and so then , you really have , essentially , fired the neuron . so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? in general , if you 're trying to transfer a current , the ideal thing to do is , the thing that you 're transferring the current down should conduct really well . or you could say it has low resistance . but you want it to be surrounded by an insulator . you want it to be surrounded . so if this was a cross section , you want it to be surrounded by an insulator that has high resistance . and the reason is because you do n't want the potential to leak across your membrane -- high resistance right over here . if you did n't have something high resistance around it , your current would actually go slower . this is true if you 're just dealing with electronics . if you just had a bunch of copper wires on one side , and you had some copper wires that were surrounded by a really good insulator , a really good resistor -- for example , plastic or rubber of some kind . the current is actually going to have less energy loss . it 's going to travel faster when it 's surrounded by an insulator . so you might say , ok , well gee . the best thing to do would be to surround this entire axon with a good insulator . and for the most part , that is true . it is surrounded by a good insulator . that is what the myelin sheath is . so let 's say we want to surround this whole thing with just one big grouping of schwann 's cells , so one big myelin sheath -- which is a good insulator . it does not conduct current well . so this right over here is just one big myelin sheath right over here . now , what 's the problem with this ? well , if this axon is really long -- and let 's say , you know , you 're a dinosaur or something . and you 're trying to go up your neck , and your neck is 20 feet long . or even a human being , we 're a reasonable size . and you 're going several feet , or even whatever , you want to go a reasonable distance purely with electrotonic spread , your signal , remember , it dissipates . your signal is going to be really weak right over here . you 're going to have a weak signal on the other end . it might not be even strong enough to make anything interesting happen at these terminals , which would n't be strong enough to trigger , maybe , other neurons , or whatever else might need to happen at this other end . so then you say , ok , well then why do n't we try to boost the signal ? well , how would you boost the signal ? you say , ok . i like having this myelin sheath . but why do n't we put gaps in the myelin sheath every so often ? and then those gaps would allow the membrane to interface with the outside . and in those areas , we could put some voltage-gated channels that can release action potentials , in order to essentially boost the signal . and that 's is exactly what the anatomy of a typical neuron is like . so instead of just one big insulating sheath like this , it would -- let me make some gaps here . whoops , i 'm going to do that in black . so actually , let me just draw it like this . let me just erase this . so clear , and let me clear this . that 's good enough . and so what we could do is we could put gaps in it right over here where the axon , the axonal membrane itself can interface with its surroundings . and of course , we know we call those gaps the nodes of ranvier , or ran-veer . i 'm not really sure how to pronounce it . so let me put those gaps in here . so you put those gaps in here , so these are the myelin sheath . and this right over here is a node of ranvier . these are nodes of ran-veer , or ranvier . and right in those little nodes , right in those nodes , right where the myelin sheath is n't , we can put these voltage-gated channels to essentially boost the signal . if the signal had to go electrotonically all the way over here , it 'd be very weak . it 's going to dissipate as it goes down , but it could be just strong enough right at this point in order to trigger these voltage-gated channels , in order to essentially boost the signal again , in order to trigger an action potential , boost the signal . and now the signal is boosted , it 'll dissipate , dissipate , dissipate , boost . and it 'll boost right over here again . and then it 'll dissipate , dissipate , dissipate , and boost . dissipate , dissipate , boost . and so by having this combination , you want the myelin sheath . you want the insulator in order to keep the transmission of the current to fast , in order to have minimal energy loss . but you do need these areas where the myelin sheath is n't in order to boost the signal , in order for the action potentials to get triggered , and so your signal can keep being -- well , i guess keep being amplified , if we wanted to talk in kind of electrical engineering speak . and this type of conduction , where the signal just keeps boosting , and if you were just to superficially observe it , it looks like the signal is almost jumping . it gets triggered here , then it gets triggered , here then it gets triggered here , then it gets triggered here , then it gets triggered here . this is called saltatory conduction . it comes from the latin word saltare -- once again , i do n't know how to pronounce . my latin is n't too good . but it comes from the latin word saltare , which means to jump around or to hop around . and that 's because it looks like the signal is hopping around . but that 's not exactly what 's happening . the signal is traveling passively through . it gets triggered here in the axon hillock . then it travels passively through electrotonic spread . and then it gets boosted . and you have the myelin sheath around it to make sure it goes as fast as possible , and you get very little loss of signal . and then it gets boosted at the nodes of ranvier , because it triggers these voltage-gated channels again . that triggers an action potential . and then your signal gets boosted , and then it dissipates -- boosted , dissipates , boosted , dissipates , boosted , dissipates . maybe it could even get boosted again . and then it can trigger whatever else it has to trigger . | so now all sorts of positive charge gets flushed into the neuron . and then purely through electrotonic spread , you will have this electrotonic potential spread down the axon . now , this is the interesting part , because we can think a little bit about , what is the best way for an axon to be designed ? | what is the initial impulse which triggers the signal spread down the axon ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | when you divide decimals is it the same as when you divide numbers above 1 ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . | why do you make the numbers diffrent colers ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . | when we divide and theres a number that keeps going when do we know when to stop putting that number after the decimal point ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | how do you use remainders in decimals ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . | when will we need to divid decimals in real life ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . | how do you divide a decimal by a whole number for example 4.3 divided by 10 ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? | when you write 30 x 42 x 100 =3,024 why do you leave off the .24 ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . | how come sal switched up the numbers ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . | why did n't sal put the zeroes during the division problem ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | this is equal to 72 . just like that . | why exactly when working with decimals like this , does multiplying the factors give the same answe r as not doing so ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . | why did you put the numbers wrong ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | when you divide decimals ca n't you just divide normally and and the decimal point ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . | who even got the idea of decimals ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | how do you divide the 30.24 by 0.42 ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? | when sal accidentally switched the numbers from 30.24 to 30.42 , would n't that affect the outcome ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | what would be a way of overlapping and justifying a solution to the equation ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . | what would /are equations for colors ? |
let 's see if we can divide 30.24 divided by 0.42 . and try pausing the video and solving it on your own before i work through it . so there is a couple of ways you can think about it . we could just write it as 30.24 divided by 0.42 . but what do you do now ? well the important realization is , is when you 're doing a division problem like this , you will get the same answer as long as you multiply or divide both numbers by the same thing . and to understand that , rewrite this division as 30.42 over 0.42 . we could write it really as a fraction . and we know that when we have a fraction like this we 're not changing the value of the fraction if we multiple the numerator and the denominator by the same quantity . and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . so lets do that . if we multiply the denominator by 100 in order to not change the value of this , we also need to multiply the numerator by 100 . we are essentially multiplying by 100 over 100 , which is just 1 . so we 're not changing the value of this fraction . or , you could view this , this division problem . so this is going to be 30.42 times 100 . move the decimal two places to the right , gets you 3,042 . the decimal is now there if you care about it . and , 0.42 times 100 . once again move the decimal one , two places to the right , it is now 42 . so this is going to be the exact same thing as 3,042 divided by 42 . so once again we can move the decimal here , two to the right . and if we move that two to the right , then we can move this two to the right . or we need to move this two to the right . and so this is where , now the decimal place is . you could view this as 3,024 . let me clear that 3024 divided by 42 . let me clear that . and we know how to tackle that already , but lets do it step by step . how many times does 42 go into 3 ? well it does not go at all , so we can move on to 30 . how many times does 42 go into 30 ? well it does not go into 30 so we can move on to 302 . how many times does 42 go into 302 ? and like always this is a bit of an art when your dividing by a two-digit or a multi-digit number , i should say . so lets think about it a little bit . so this is roughly 40 . this is roughly 300 . so how many times does 40 go into 300 ? well how many times does 4 go into 30 ? well , it looks like it 's about seven times , so i 'm going to try out a 7 , see if it works out . 7 times 2 is 14 . 7 times 4 is 28 . plus 1 is 29 . and now i can subtract . do a little bit of re-grouping here . so lets see , if i regroup -- i take a 100 from the 300 . that becomes a 200 . then our zero tens , now i have 10 tens , but i 'm going to need one of those 10 tens , so that 's going to be 9 tens . and i 'm going to give it over here . so this is going to be a 12 . 12 minus 4 is 8 . 9 minus 9 is 0 . 2 minus 2 is 0 . so what i got left over is less than 42 , so i know that 7 is the right number . i want to go as many times as possible into 302 without going over . so now lets bring down the next digit . lets bring down this 4 over here . how many times does 42 go into 84 ? well that jumps out at you , or hopefully it jumps -- it goes two times . 2 times 2 is 4 . 2 times 4 is 8 . you subtract , and we have no remainder . so 3,042 divided by 42 is the same thing as 30.42 divided by 0.42 . and it 's going to be equal to 72 . actually , i did n't have to copy and paste that , i 'll just write this . this is equal to 72 . just like that . | and so what could we multiply this denominator by to make it a whole number ? well we can multiply it by 10 and then another 10 . so we can multiply it by a 100 . | say i had 34.4 but also had 0.00534 and multiplied the second one by 10,000 does 34.4 have to be multiplied by 10,000 too ? |
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