Explain the following processes:
(a) Polarisation of the membrane of a nerve fibre.
(b) Depolaristion of the membrance of a nerve fibre.
(c ) Conduction of nerver impulse along a nerve fibre.
(d) Transmission of a berve impulse across a chemical synapse.

Explanation

(a) During resting condition, the conectration of `k+` ions is more inside the axoplasm while the concetration of `N+` ions is more outside the axoplasm. As a result, the potassium ions move faster from inside to oustide as compared to sodium. Therefore, the membrance becomes positively charged outside and negatively charged inside.
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(b) When an electrical stimulus is given to a nerve fibre, an action potential is gnerated. The membrance charge outside the nerve fibre.
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(c) There are two type of nerve fibre-myelinated and non-myleinated . In myellinated nerve fibre, the action potential is conducted form node to node in jumping manner. Myellinated nerve fibre is coated with myellin not possible along the whole lenght of never fibre. It take place only at some point. know as node of Ranvir, whereas in non-myelinated nerve fibre,the ionic exchanges and depolariztion of nerve fibre takes place along the whole lenght of the nerver fibre. Because of this ionic exchage, the deplarized area becomes repolarized and the next polarized area becomes depolarized.
(d) Synapse is small gap that occurs between the last portion of the axon of one neuron and the dendrite of next neuron. An impulse reaches at the end plate of axon, vesicles consisitng fo chemical substance or nerurotransmitter, such as acetylcholine , fuse with the plasma membrance . This chemical moves across the cletf and attaches to chemo-recptors present on the membrance and genertes a nerver implus across nerver fibre. The chemical, acetcholinestrase. The enzyme is present in the post synaptic membrace of the dendrite .
It hydrolyse acetylcholine and this allows the membrane to repolarize.
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