Question

Question #4b95c

Answer 1

Myelin is an insulating white coloured casing that surrounds the glial cells in axons of some neurons.

Explanation:

It is mostly called as myelin sheath(covering) and is made up of phospholipids and proteins. In case of neurons present in `"CNS"`, myelin sheath is produced by oligodendrocytes . While in neurons if `"PNS"`, it is secreted by schwann cells . The purpose of this sheath is to provide extra protection to the neuron. This is also salient in nourishment of nerve tract or axon. It allows the nerve impulse to travel much more quickly.

The axon is tail like projection of cell body of neuron. The axons of some neurons have this sheath & are called myelinated neurons while the other that are deprived of this sheath are called non-myelinated neurons. In myelinated neurons, the myelin sheath is not continuous rather it has gaps called nodes of ranvier. These are the portions of axon which don't have any covering, thus, are exposed to the extracellular space.

Thus, in case of myelinated neurones the passage of nerve impulse is hindered by these insulating myelin sheaths. So, the nerve impulse jumps from node to node and this type of impulse is specifically called as saltatory impulse. In this case the nerve impulse doesn't have to travel the whole length of neuron because it just hops from one node to the next. So, the speed of impulse tremendously increases.

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