Q.At the end of repolarization, the nerve membrane gets hyperpolarized. Why?

Hyperpolarization at the end of repolarization happens because the voltage-gated K+ channels, which opened during repolarization, are slow to close — so K+ keeps leaving the neuron a bit longer than needed, briefly overshooting the resting potential to a more negative value.

During a nerve impulse (action potential), the neuron membrane goes through distinct phases:

1. Depolarization: voltage-gated Na+ channels open, Na+ rushes in, making the inside of the membrane positive.
2. Repolarization: Na+ channels close/inactivate, and voltage-gated K+ channels open, allowing K+ to rush OUT of the cell, bringing the membrane potential back down towards (and then past) the resting potential.
3. Hyperpolarization (after-hyperpolarization): the K+ channels that opened during repolarization do not close immediately once the membrane reaches the normal resting potential — they remain open a little longer. This continued outflow of K+ ions makes the inside of the membrane even MORE negative than the normal resting potential for a brief period, before the K+ channels finally close and other ion pumps (like the Na+-K+ pump) restore the true resting potential. …