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Observe the permanent slide of nerve cell or neuron under microscope |
draw and label its parts, compare with the following diagram. |
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dendrites Each nerve cell consists of a cell body with |
nissl’s granules a prominent nucleus. There are fine projections |
nucleus mainly of two types extending from the cell body |
cell body of the nerve cell. The small projections are |
dendrites while a long one that extends to |
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schwann cell |
different parts of our body is called Axon. The |
fig-3: axon axon is surrounded by a specialized insulatory |
Nerve cell node of ranvier sheath called myelin sheath.This sheath is |
myelin sheath interrupted at regular intervals called nodes of |
synaptic knob ranvier.The myelin sheath is made up of schwann |
cells and chiefly consists of fatty material. |
axon terminal Axons not having the sheath are non-myelinated |
96 X Class Coordination - The liking system |
fibers. The covering also forms a partition between adjacent axons. The |
nerve cell body lies either in our brain or spinal cord or very close to the |
spinal cord in a region called dorsal or ventral root ganglion. In the brain |
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or spinal cord, it is difficult to make out the difference between dendrites |
and axons on the basis of their length, often, the presence of the sheath |
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helps us to find out but several axons here do not have the sheath. |
We know that the nerve cell is the structural and |
functional unit of nervous system. Our nervous system |
consists of more than100 billion of them, which |
communicate with each other in a specific manner. |
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Synapse |
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Dendrites of one nerve cell connect to the other or |
to the axons of the other nerve cell through |
connections called as a ‘synapse’. |
Synapse is the functional region of contact |
between two neurons, where information from one |
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neuron is transmitted or relayed to another neuron. fig-4: Synapse |
Though these are regions of minute gaps and essentially neurons do not |
have any protoplasmic connection between them yet information is passed |
from one nerve cell to the other through these gaps either in the form of |
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chemical or electrical signals or both. These synapses are mainly found |
on the brain, spinal cord and around the spinal cord. Beyond these areas |
the axon carries the signals to respective areas in our body. |
Pathways: From stimulus to response |
In the holding stick activity you observed that there is coordination |
between eye and finger. Different pathways are taken by nerves to bring |
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about this coordinated activity. |
On the basis of pathways followed, nerves are classified mainly into |
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three different types. They are as follows. |
Afferent nerves or Sensory nerves : |
(a) Afferent (or ferrying towards) which carry messages towards the |
central nervous system (spinal cord or brain) from nerve endings on the |
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muscles of different sense organs that sense the change in surroundings |
are called stimulus detectors. These are also called ‘sensory’ nerves. |
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fig-5: Sensory neuron |
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Free distribution by T.S. Government 2019-20 97 |
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