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Bundle of His Purkinje fibers P wave in ECG QRS wave in ECG FIGURE 52.16 The path of electrical excitation in the heart. A wave of depolarization begins at the sinoatrial (SA) node. After passing over the atria and causing them to contract (forming the P wave on the ECG), the depolarization reaches the atrioventricula... |
a network of fibers called the atrioventricular bundle or bundle of His. It is then transmitted by Purkinje fibers, which directly stimulate the myocardial cells of the ventricles. The rapid conduction of the depolarization along the bundle of His and the Purkinje fibers causes the almost simultaneous contraction of t... |
to the heart more rapidly. In addition, the ventricles contract more strongly, so they empty more completely with each beat. During exercise, the cardiac output increases to a maximum of about 25 liters per minute in an average young adult. Although the cardiac output has increased five times, not all organs receive f... |
uitary gland in response to an increase in the osmotic concentration of the blood plasma. Dehydration, for example, causes the blood volume to decrease while the remaining plasma becomes more concentrated. This stimulates osmoreceptors in the hypothalamus of the brain, a region located immediately above the pituitary. ... |
rine hormone, is produced by one cell, penetrates through membranes, and alters the activities of other (a) (b) (c) FIGURE 52.17 Atherosclerosis. (a) The coronary artery shows only minor blockage. (b) The artery exhibits severe atherosclerosis—much of the passage is blocked by build-up on the interior walls of the arte... |
of a stroke depend on how severe the damage is and where in the brain the stroke occurs. Atherosclerosis is an accumulation within the arteries of fatty materials, abnormal amounts of smooth muscle, deposits of cholesterol or fibrin, or various kinds of cellular debris. These accumulations cause blood flow to be reduc... |
, metabolites, wastes, and hormones are dissolved in the plasma. • Erythrocytes, or red blood cells, contain hemoglobin and function to transport oxygen; the leukocytes, or white blood cells, function in immunological defenses. • The heart pumps blood into arteries, which branch into smaller arterioles. • Blood from th... |
bed anatomy Human circulatory system Lymphatic system Lymphoid organs • Lymphatic system • Vessels and pressure • Blood • Lymph system • Plasma • On Science Article: Dinosaur hearts • Art Activities: External heart anatomy Internal view of heart • Cardiac cycle blood flow • Art Activity: Plaque • Blood flow • Cardiac ... |
can hold their breath for over two hours, descend and ascend rapidly in the water, and endure repeated dives without suffering any apparent respiratory distress. Animals pry energy out of food molecules using the bio- chemical process called cellular respiration. While the term cellular respiration pertains to the use... |
evolution of respiratory systems has involved changes in all of these factors. Fick’s Law of Diffusion states that the rate of diffusion across a membrane depends on surface area, concentration (partial pressure) difference, and distance. CO2 O2 Epidermis CO2 O2 Epidermis Papula O2 CO2 (a) Blood vessel (b) (c) Spiracl... |
environment (either water or air) close to the internal fluid, which is usually circulated throughout the body. The respiratory organs thus increase the rate of diffusion by maximizing surface area and decreasing the distance the diffusing gases must travel (the A and d factors, respectively, in the Fick equation). At... |
PN2 PO2 PCO2 = 760 7902% = 6006mm Hg, = 760 2095% = 1592mm Hg, and = 760 0.03% = 0.2mm Hg. Humans do not survive long at altitudes above 6000 meters. Although the air at these altitudes still contains 20.95% oxygen, the atmospheric pressure is only about 380 mm Hg, so its PO2 is only 80 mm Hg (380 × 20.95%), only half... |
the gills. Contraction of the muscular walls of the mantle cavity draws water in and then expels it. In crustaceans, the branchial chamber lies between the bulk of the body and the hard exoskeleton of the animal. This chamber contains gills and opens to the surface beneath a limb. Movement of the limb draws water thro... |
advantages of a countercurrent flow system were discussed in chapter 52 in relation to temperature regulation and are again shown here in figure 53.6a. Blood low in oxygen en- Operculum Oral valve Buccal cavity Gills Opercular cavity Mouth opened, jaw lowered Mouth closed, operculum opened (a) (b) 1056 Part XIII Anima... |
.6b). The concentration difference would fall rapidly, however, as the water lost oxygen to the blood. Net diffusion of oxygen would cease when the oxygen concentration of blood matched that of the water. At this point, much less oxygen would have been transferred to the blood than is the case with countercurrent flow.... |
for respiration by terrestrial vertebrates. Respiration in AirBreathing Animals Despite the high efficiency of gills as respiratory organs in aquatic environments, gills were replaced in terrestrial animals for two principal reasons: 1. Air is less buoyant than water. The fine membranous lamellae of gills lack structu... |
7). A lung minimizes evaporation by moving air through a branched tubular passage; the air becomes saturated with water vapor before reaching the portion of the lung where a thin, wet membrane permits gas exchange. The lungs of all terrestrial vertebrates ex- Air is piped directly to the body cells of insects, but the ... |
metabolisms are slow. Lung function becomes more important during the summer as the frog’s metabolism increases. Although not common, some terrestrial amphibians, such as plethodontid salamanders, rely on cutaneous respiration exclusively. Reptiles expand their rib cages by muscular contraction, and thereby take air i... |
an extremely extensive capillary network. All gas exchange between the air and blood takes place across the walls of the alveoli. The branching of bronchioles and the vast number of alveoli combine to increase the respiratory surface area (A in Fick’s Law) far above that of amphibians or reptiles. In humans, there are... |
There are two groups of air sacs, anterior and posterior. When they are expanded during inspiration they take in air, and when they are compressed during expiration they push air into and through the lungs. If we follow the path of air through the avian respiratory system, we will see that respiration occurs in two cy... |
posterior group, that extend between the internal organs and into the bones. (c) Breathing occurs in two cycles. Cycle 1: Inhaled air (shown in red) is drawn from the trachea into the posterior air sacs and then is exhaled into the lungs. Cycle 2: Air is drawn from the lungs into the anterior air sacs and then is exha... |
. A second, parietal pleural membrane lines the inner wall of the thoracic cavity. The space between these two membranes, the pleural cavity, is normally very small and filled with fluid. This fluid links the two membranes in the same way a thin film of water can hold two plates of glass together, effectively coupling ... |
force a deeper inspiration by contracting other muscles that insert on the sternum or rib cage and expand the thoracic cavity and lungs to a greater extent (figure 53.12a). The thorax and lungs have a degree of elasticity—they tend to resist distension and they recoil when the distend- Sternocleidomastoid muscles cont... |
be clinically important, because an abnormally low vital capacity may indicate dam- age to the alveoli in various pulmonary disorders. For example, in emphysema, a potentially fatal condition usually caused by cigarette smoking, vital capacity is reduced as the alveoli are progressively destroyed. A person normally br... |
. You can demonstrate this mechanism by simply holding your breath. Your blood carbon dioxide immediately rises and your blood oxygen falls. After a short time, the urge to breathe induced by the changes in blood gases becomes overpowering. This is due primarily to the rise in blood carbon dioxide, as indicated by a ri... |
Actually, in people with normal lungs, PO2 becomes a significant stimulus for breathing only at high altitudes, where the PO2 is low. Low PO2 can also stimulate breathing in patients with emphysema, where the lungs are so damaged that blood CO2 can never be adequately eliminated. Breathing serves to keep the blood gas... |
oxygen’s low solubility in water, however, blood plasma can contain a maximum of only about 3 milliliters O2 per liter. Yet whole blood carries almost 200 milliliters O2 per liter! Most of the oxygen is bound to molecules of hemoglobin inside the red blood cells. Hemoglobin is a protein composed of four polypeptide ch... |
hemoglobin within red blood cells is in the form of oxyhemoglobin—indicated as a percent oxyhemoglobin saturation of 97%. As the blood travels through the systemic blood capillaries, oxygen leaves the blood and diffuses into the tissues. Consequently, the blood that leaves the tissue in the veins has a PO2 that is dec... |
dioxide more rapidly during exercise and active muscles produce heat, the blood unloads a higher percentage of the oxygen it carries during exercise. Deoxyhemoglobin combines with oxygen in the lungs to form oxyhemoglobin, which dissociates in the tissue capillaries to release its oxygen. The degree to which the loadi... |
of CO2 with water to form carbonic acid (H2CO3). Carbonic acid dissociates into –) and hydrogen (H+) ions. The H+ bicarbonate (HCO3 binds to deoxyhemoglobin, and the bicarbonate moves out of the erythrocyte into the plasma via a transporter that exchanges one chloride ion for a bicarbonate (this is called the “chlorid... |
H2O H2CO3 H2CO3 H+ + HCO3 – H+ combines with hemoglobin Cl– – HCO3 Plasma Red blood cells Plasma CO2 + H2O H2CO3 Hemoglobin + CO2 HCO3 – + H+ H2CO3 HCO3 – Cl– FIGURE 53.18 The transport of carbon dioxide by the blood. CO2 is transported in three ways: dissolved in plasma, bound to the protein portion of hemoglobin, an... |
com Questions Media Resources 53.1 Respiration involves the diffusion of gases. • The factors that influence the rate of diffusion, surface area, concentration gradient, and diffusion distance, are described by Fick’s Law. • Animals have evolved to maximize the diffusion rate across respiratory membranes by increasing ... |
the blood goes through the systemic capillaries. • Carbon dioxide combines with water as the carbon dioxide is transported to the lungs for exhalation. 1070 Part XIII Animal Form and Function 6. How are the lungs connected to and supported within the thoracic cavity? 7. How does the brain control inspiration and expir... |
rupting pollutants contaminate Florida lakes, their presence can be detected by its impact on the sexual development of the lakes’ resident alligators. Just as the death of coal miners’ canaries warn of the buildup of dangerous gas within the shaft of coal mines, so disruption of the sexual development of alligators ca... |
.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Lake (b) E/A ratio Alligator sexual development inhibited by contamination. (a) Ratio of estrogen/androgen (E/A) plasma concentrations in large juvenile alligators 3-7 years old. A relatively larger ratio in males is atypical and indicates an estrogenic hormonal environment, as opposed to... |
lakes studied, female alligators showed a much higher E/A ratio than males (graph a above), a normal result. The exceptions are Lake Griffin and Lake Apopka, the most polluted of the lakes. The larger E/A ratio observed in male alligators caught from these two lakes indicates an estrogenic hormonal environment in thes... |
urons form junctions called synapses with other cells. Structure of Synapses. Neurotransmitters diffuse across to the postsynaptic cell and combine with receptor proteins. Neurotransmitters and Their Functions. Some neurotransmitters cause a depolarization in the postsynaptic membrane; others produce inhibition by hype... |
described in chapter 49, the nervous system consists of neurons and supporting cells. Sensory (or afferent) neurons carry impulses from sensory receptors to the central nervous system (CNS); motor (or efferent) neurons carry impulses from the CNS to effectors—muscles and glands (figure 54.2). In addition to sensory an... |
sheath Myelin sheath Node of Ranvier FIGURE 54.4 Structure of a typical neuron. Extending from the cell body are many dendrites, which receive information and carry it to the cell body. A single axon transmits impulses away from the cell body. Many axons are encased by a myelin sheath, whose multiple membrane layers f... |
in a cable, to form nerves. The myelin sheath is interrupted at intervals of 1 to 2 mm by small gaps known as nodes of Ranvier (see figure 54.4). The role of the myelin sheath in impulse conduction will be discussed later in this chapter. Neurons and neuroglia make up the central and peripheral nervous systems in vert... |
in the plasma membrane have gates, portions of the channel protein that open or close the channel’s pore. In the axons of neurons and in muscle fibers, the gates are closed or open depending on the membrane potential. Such channels are therefore known as voltage-gated ion channels (figure 54.7). In most cells, the per... |
ulating the Animal Body Table 54.1 The Ionic Composition of Cytoplasm and Extracellular Fluid (ECF) Concentration Concentration in Cytoplasm (mM) in ECF (mM) 15 150 7 150 5 110 Equilibrium Potential (mV) +60 –90 –70 Ratio 10:1 1:30 15:1 Ion Na+ K+ Cl– Channel closed Channel open Gate + – + + ving K+ into the cell, ther... |
uneven distribution of charges, where the inside of the membrane is negatively charged in comparison with the outside (–70 mV). The magnitude, measured in millivolts, of this potential difference primarily reflects the difference in K+ concentration. FIGURE 54.7 Voltage-gated ion channels. In neurons and muscle cells,... |
that the positive sign indicates that the membrane reverses polarity as Na+ rushes in). 62mV 64mV 66mV 68mV 70mV 72mV 74mV E1 2 E2 3 I 4 E1 E2 I FIGURE 54.9 Graded potentials. (1) A weak excitatory stimulus, E1, elicits a smaller depolarization than (2) a stronger stimulus, E2. (3) An inhibitory stimulus, I, produces ... |
+ channels allows K+ to diffuse out of the cell, repolarizing the plasma membrane. On an oscilloscope, this repolarization of the membrane appears as the falling phase of the action potential. In many cases, the repolarization carries the membrane potential to a value slightly more negative than the resting potential f... |
+ + + + + + + + – – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + + – – – – – – – – – + Na+ – + – – + + + + + + + + – – – – – – Depolarized Na+ + – K+ + – – – + + + + – + + + – – – – – – Repolarized Na+ + – + – – – – + – – – + + – – – + + + + + – Resting K+ K+ + + + – – – + + – – – – + + – – – – + Na+ ... |
nervous transmission, return for a moment to the “wave” analogy used on the previous page to describe propagation of an action potential. The “wave” moves across the seats of a crowded stadium as fans standing up in one section trigger the next section to stand up in turn. Because the “wave” will skip sections of empt... |
swollen and contains numerous synaptic vesicles, which are each packed with chemicals called neurotransmitters. When action potentials arrive at the end of the axon, they stimulate the opening of voltage-gated Ca++ channels, causing a rapid inward diffusion of Ca++. This serves as the stimulus for the fusion of the sy... |
Acetylcholine binds to its receptor proteins in the postsynaptic membrane and thereby causes ion channels within these proteins to open (figure 54.16). The gates to these ion channels are said to be chemically gated because they open in response to ACh, rather than in response to depolarization. The opening of the che... |
of the fastest known, cleaving ACh into inactive fragments. Nerve gas and the agricultural insecticide parathion are potent inhibitors of AChE and in humans can produce severe spastic paralysis and even death if the respiratory muscles become paralyzed. Although ACh acts as a neurotransmitter between motor neurons and... |
acid tyrosine and are included in the subcategory of catecholamines. Serotonin is a biogenic amine derived from a different amino acid, tryptophan. Dopamine is a very important neurotransmitter used in the brain to control body movements and other functions. Degeneration of particular dopamine-releasing neurons produc... |
blocking reabsorption of serotonin in the synapse, making up for the shortage. Axon (a) (b) FIGURE 54.19 Integration of EPSPs and IPSPs takes place on the neuronal cell body. (a) The synapses made by some axons are excitatory (blue); the synapses made by other axons are inhibitory (red). The summed influence of all of... |
also released as a neurotransmitter in the brain, and has been implicated in the processes of learning and memory. Synaptic Integration The activity of a postsynaptic neuron in the brain and spinal cord of vertebrates is influenced by different types of input from a number of presynaptic neurons. For example, a single... |
and more dopamine is added, firing the pleasure pathway more and more often (figure 54.20). When receptor proteins on limbic system nerve cells are exposed to high levels of dopamine neurotransmitter molecules for prolonged periods of time, the nerve cells “turn down the volume” of the signal by lowering the number of... |
down the volume” in two ways: (1) by making fewer receptor proteins to which nicotine can bind; and (2) by altering the pattern of activation of the nicotine receptors (that is, their sensitivity to neurotransmitter). It is this second adjustment that is responsible for the profound effect smoking has on the brain’s a... |
nicotine with willpower, any more than willpower can stop a bullet when playing Russian roulette with a loaded gun. If you smoke cigarettes for a prolonged period, you will become addicted. What do you do if you are addicted to smoking cigarettes and you want to stop? When use of an addictive drug like nicotine is sto... |
and little coordination The simplest animals with associative activity in the nervous system are the free-living flatworms, phylum Platyhelminthes. Running down the bodies of these flatworms are two nerve cords; peripheral nerves extend outward to the muscles of the body. The two nerve cords converge at the front end ... |
the spinal cord devoted primarily to coordinating motor reflexes. Tracts containing large numbers of axons run like cables up and down the spinal cord to the hindbrain. The hindbrain, in turn, integrates the many sensory signals coming from the muscles and coordinates the pattern of motor responses. Much of this coord... |
Midbrain (Mesencephalon) Hindbrain (Rhombencephalon) Spinal cord Diencephalon Telencephalon Forebrain (Prosencephalon) Telencephalon Mesencephalon Cerebellum Cerebrum Thalamus Hypothalamus Optic tectum Pons Medulla oblongata Spinal cord Diencephalon Cerebellum Medulla oblongata Pons Pituitary gland 5 weeks 8 weeks 11 ... |
The dominance of the cerebrum is greatest in humans, in whom it envelops much of the rest of the brain. 1090 Part XIV Regulating the Animal Body see a remarkable difference between fishes and reptiles, on the one hand, and birds and mammals, on the other. Mammals have brains that are particularly large relative to the... |
1000 100 10 1 0.1 Homo sapiens • • Elephant • Porpoise Australopithecus Baboon • Wolf • • • • • Lion Chimpanzee Male gorilla • Blue whale Crow • Vampire bat • Opossum • Rat • • Mole 0.01 0.1 1 Vertebrates 10 (a) 100 1000 10,000 0.01 0.1 1 Body mass in kilograms Mammals 10 (b) 100 1000 10,000 FIGURE 54.26 Brain mass ve... |
cortex lies along the gyrus (convolution) on the posterior border of the frontal lobe, just in front of the central sulcus (crease) (figure 54.28). Each point on its surface is associated with the movement of a different part of the body (figure 54.29). Just behind the central sulcus, on the anterior edge of the parie... |
indicated in this stylized map. The areas of the body are drawn in proportion to the amount of cortex dedicated to their sensation or control. For example, the hands have large areas of sensory and motor control, while the pharynx has a considerable area of motor control but little area devoted to the sensations of th... |
are responsible for emotional responses. The hippocampus is also believed to be important in the formation and recall of memories, a topic we will discuss later. Chapter 54 The Nervous System 1093 Language and Other Functions Arousal and Sleep. The brain stem contains a diffuse collection of neurons referred to as the... |
and are more likely to 1094 Part XIV Regulating the Animal Body FIGURE 54.30 Different brain regions control various activities. This illustration shows how the brain reacts in human subjects asked to listen to a spoken word, to read that same word silently, to repeat the word out loud, and then to speak a word relate... |
, writing, and oral comprehension remain normal, and patients with this disability can still recognize acquaintances by their voices. The nondominant hemisphere is also important for the consolidation of memories of nonverbal experiences. Memory and Learning. One of the great mysteries of the brain is the basis of memo... |
hypotheses have been proposed: one that nerve cells in the brain are killed from the outside in, and the other that the cells are killed from the inside out. In the first hypothesis, external proteins called β-amyloid peptides kill nerve cells. A mistake in protein processing produces an abnormal form of the peptide, ... |
reflex produces a rapid motor response to a stimulus because the sensory neuron passes its information to a motor neuron in the spinal cord, without higher level processing. One of the most frequently used reflexes in your body is blinking, a reflex that protects your eyes. If anything, such as an insect or a cloud of... |
brates, however, involve a single connecting interneuron between the sensory and the motor neuron. The withdrawal of a hand from a hot stove or the blinking of an eye in response to a puff of air involve a relay of information from a sensory neuron through one or more interneurons to a motor neuron. The motor neuron th... |
origin, a spinal nerve separates into sensory and motor components. The axons of sensory neurons enter the dorsal surface of the spinal cord and form the dorsal root of the spinal nerve, whereas motor axons leave from the ventral surface of the spinal nerve and form the ventral root of the spinal nerve. The cell bodie... |
Two Acetylcholine Acetylcholine Norepinephrine Effect on motor nerves Innervation of effector cells Number of neurons in path to effector Neurotransmitter The Autonomic Nervous System Autonomic motor reflex The autonomic nervous system is composed of the sympathetic and parasympathetic divisions and the medulla oblong... |
colon contents Delay emptying Bladder Constrict Secrete saliva Parasympathetic Constrict bronchioles Slow down heartbeat Increase secretion Large intestine Increase motility Small intestine Empty colon Empty bladder FIGURE 54.36 The sympathetic and parasympathetic divisions of the autonomic nervous system. The pregang... |
medulla secretes epinephrine and norepinephrine Stomach contractions are inhibited Blood flow to skeletal muscles increases FIGURE 54.37 The sympathetic division of the nervous system in action. To prepare the body for fight or flight, the sympathetic division is activated and causes changes in many organs, glands, an... |
ion channels are located some distance away from the receptor proteins for ACh, the G proteins are needed to serve as connecting links between them. There are three G protein subunits, designated α, β, and γ, bound together and attached to the receptor protein for ACh. When ACh, released by parasympathetic endings, bi... |
. 2. Which cation is most concentrated in the cytoplasm of a cell, and which is most concentrated in the extracellular fluid? How are these concentration differences maintained? 3. What is a voltage-gated ion channel? 4. What happens to the size of an action potential as it is propagated? 54.3 Neurons form junctions ca... |
Outline 55.1 Animals employ a wide variety of sensory receptors. Categories of Sensory Receptors and Their Actions. Sensory receptors can be classified according to the type of stimuli to which they can respond. 55.2 Mechanical and chemical receptors sense the body’s condition. Detecting Temperature and Pressure. Rece... |
action potentials and the frequency of these impulses. Thus, if the auditory nerve is artificially stimulated, the brain perceives the stimulation as sound. But if the optic nerve is artificially stimulated in exactly the same manner and degree, the brain perceives a flash of light. 1103 55.1 Animals employ a wide var... |
cone cells Retina of eye Pit organ Face of snake Electricity Ampullae of Lorenzini Within skin of fishes Otoliths and hair cells Otoliths deform hair cells Collection of hair cells Collection of hair cells Chemoreceptors: epithelial cells with microvilli Chemoreceptors: ciliated neurons Hair cells between basilar and ... |
the receptor potential and the higher the frequency of action potentials. There is generally a logarithmic relationship between stimulus intensity and action potential frequency—a sensory stimulus that is ten times greater than another stimulus will produce action potentials at twice the frequency of the other stimulu... |
especially near surfaces where damage is most likely to occur. Different nociceptors may respond to extremes in temperature, very intense mechanical stimulation, or specific chemicals in the extracellular fluid, including some that are released by injured cells. The thresholds of these sensory cells vary; some nocicep... |
mechanical distortion of the membrane, initiating a depolarization (receptor potential) that causes the sensory neuron to generate action potentials. Muscle Length and Tension Buried within the skeletal muscles of all vertebrates except the bony fishes are muscle spindles, sensory stretch receptors that lie in paralle... |
blood pressure from baroreceptors within arteries. Nerve Motor neurons Sensory neurons Skeletal muscle Spindle sheath Specialized muscle fibers (spindle fibers) FIGURE 55.5 A muscle spindle is a stretch receptor embedded within skeletal muscle. Stretching of the muscle elongates the spindle fibers and stimulates the s... |
to smell. The effect of smell on the sense of taste can easily be demonstrated by eating an onion with the nose open and then eating it with the nose plugged. Like vertebrates, many arthropods also have taste chemoreceptors. For example, flies, because of their mode of searching for food, have taste receptors in senso... |
dissolve in extracellular fluid before they can activate the olfactory receptors). The sense of smell can be extremely acute in many mammals, so much so that a single odorant molecule may be all that is needed to excite a given receptor. Although humans can detect only four modalities of taste, they can discern thousa... |
with the rest of its school. It also enables a blind cave fish to sense its environment by monitoring changes in the patterns of water flow past the lateral line receptors. The lateral line system is found in amphibian larvae, but is lost at metamorphosis and is not present in any terrestrial vertebrate. The sense pro... |
(and the membranous labyrinth of the vertebrate inner ear) have a number of smaller cilia called stereocilia and one larger kinocilium. When the cilia bend in the direction of the kinocilium, the hair cell releases a chemical transmitter that depolarizes the associated sensory neuron. Bending of the cilia in the oppos... |
ium, similar to those in the lateral line system of fish. The hairlike processes are embedded within a gelatinous membrane containing calcium carbonate crystals; this is known as an otolith membrane, because of its location in the inner ear (oto is derived from the Greek word for ear). Because the otolith organ is orie... |
in the lateral line organ of fishes detect water movements, and hair cells in the vestibular apparatus of terrestrial vertebrates provide a sense of acceleration. Semicircular canals Vestibular nerves Vestibule Endolymph Flow of endolymph Cupula Cilia of hair cells Hair cells Supporting cell Vestibular nerve Stimulati... |
use their lateral line system to detect water movements and vibrations emanating from relatively nearby objects, and their hearing system to detect vibrations that originate from a greater distance. The hearing system of fish consists of the otolith organs in the membranous labyrinth (utricle and saccule) previously d... |
duct is the vestibular canal, and the area below is the tympanic canal. All three chambers are filled with fluid, as previously described. The oval window opens to the upper vestibular canal, so that when the stapes causes it to vibrate, it produces pressure waves of fluid. These pressure waves travel down to the tymp... |
bending of these cilia depolarizes the hair cells. The hair cells, in turn, stimulate the production of action potentials in sensory neurons that project to the brain, where they are interpreted as sound. Chapter 55 Sensory Systems 1115 Frequency Localization in the Cochlea Malleus Incus Stapes Oval window Vestibular ... |
of background noise, which is effectively “tuned out” by the efferent axons. 1116 Part XIV Regulating the Animal Body Tympanic membrane Round window Base High frequency (22,000Hz) Tympanic canal Apex Medium frequency (2000Hz) Low frequency (500Hz) FIGURE 55.14 Frequency localization in the cochlea. The cochlea is show... |
bats, one largely closed to birds because birds must rely on vision. There are no truly nocturnal birds; even owls rely on vision to hunt, and do not fly on dark nights. Because bats are able to be active and efficient in total darkness, they are one of the most numerous and widespread of all orders of mammals. Some m... |
tebrate Eye The eye of a human is typical of the vertebrate eye (figure 55.18). The “white of the eye” is the sclera, formed of tough connective tissue. Light enters the eye through a transparent cornea, which begins to focus the light. This Light Pigment layer Flatworm will turn away from light FIGURE 55.16 Simple eye... |
required for close vision; in far vision, the ciliary muscles relax, moving away from the lens and tightening the suspensory ligament. The lens thus becomes more flattened and less powerful, keeping the image focused on the retina. People who are nearsighted or farsighted do not properly focus the image on the retina ... |
outer segment, which is packed with hundreds of flattened discs stacked on top of one another. The light-capturing molecules, or photopigments, are located on the membranes of these discs. In rods, the photopigment is called rhodopsin. It consists of the protein opsin bound to a molecule of cis-retinal (figure 55.21),... |
rods and cones synapse 1120 Part XIV Regulating the Animal Body Outer segment Connecting cilium Inner segment Mitochondria Nucleus Synaptic terminal Pigment discs FIGURE 55.20 Rods and cones. The pigment-containing outer segment in each of these cells is separated from the rest of the cell by a partition through which... |
This flow of Na+ that occurs in the absence of light is called the dark current, and it causes the membrane of a photoreceptor to be somewhat depolarized in the dark. In the light, the Na+ channels in the outer segment rapidly close, reducing the dark current and causing the photoreceptor to hyperpolarize. Researchers... |
other types of cells in the retina before it reaches the rods and cones. Once the photoreceptors are activated, they stimulate bipolar cells, which in turn stimulate ganglion cells. The direction of nerve impulses in the retina is thus opposite to the direction of light. Amacrine cell Cone Horizontal cell Rod Chapter ... |
more likely to be color blind than women, because the trait for color blindness is carried on the X chromosome; men have only one X chromosome per cell, whereas women have two X chromosomes and so can carry the trait in a recessive state. Binocular Vision Primates (including humans) and most predators have two eyes, o... |
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