Answer: Option A
:
A
When a nerve fibre is stimulated, the permeability of membrane to Na⁺ is greatly increased at the point of stimulus (rapid influx of Na⁺) and hence polarity of membrane is reversed and now membrane is said to be depolarized.
1. The electric potential difference across the plasma membrane at that site is called action potential, which in fact termed as nerve impulse.
2. Depolarization is very rapid, so that conduction of nerve impulse along the entire length of axon occurs in fractions of second.
3. Depolarization is followed by the increase in membrane permeability of K⁺ which leads to change in polarization i.e. +ve charge outside and –ve charge inside. It is called repolarization.