ANATOMY

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: -During the depolarization phase, the gated sodium ion channels on the neuron’s membrane suddenly open and allow sodium ions (Na+) present outside the membrane to rush into the cell. As the sodium ions quickly enter the cell, the internal charge of the nerve changes from-70 mV to-55 mV.

Detailed explanation-3: -They are the first channels to open in response to changes in voltage, allowing positively charged sodium ions to accumulate in the interior of the cell.

Detailed explanation-4: -Depolarization of the plasma membrane due to opening of gated Na+ channels. (a) Resting neurons non gated K+ channels are open, but the more numerous gated Na+ channels are closed. The movement of K+ ions outward establishes the inside-negative membrane potential characteristic of most cells.

Detailed explanation-5: -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.