Explain the following processes :
Depolarisation of the membrane of a nerve fibre

Explanation

Depolarisation of the membrane of a nerve fibre : On being excited by a stimulus, the permeability of neural membrane for `Na^(+)` and `K^(+)` ions is reversed and `Na^(+)-K^(+)` exchange pump also starts functioning in reverse direction. Due to increase in `Na^(+)` ion concentration, the inner surface of neural membrane becomes positive and outer surface negative. It results in the depolarisation of the membrane.