GENERAL HISTOLOGY

Detailed explanation-1: -In neurons, the rapid rise in potential, depolarization, is an all-or-nothing event that is initiated by the opening of sodium ion channels within the plasma membrane. The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels.

Detailed explanation-2: -Therefore, when the Na+ channels open and spontaneously inactivate, it takes time (several msec) for them to recover from that inactivation. This process of recovery from inactivation underlies the absolute refractory period. During an action potential the Na+ channels open and then they become inactivated.

Detailed explanation-3: -Voltage-gated ion channels typically are closed at the resting membrane potential but open upon membrane depolarization. These channels detect changes in electric potential across the membrane through a domain responsible for sensing voltage.