ANATOMY

Detailed explanation-1: -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-2: -Na+ channels in the axon hillock open, allowing positive ions to enter the cell (Figure 1). Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV.

Detailed explanation-3: -Depolarization is the first step in an action potential. In this step the voltage-gated sodium channels open due to an external stimulus. These channels permit rapid flow of sodium ions into the cell. This changes the polarity of the cell and causes the membrane potential to increase.

Detailed explanation-4: -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.