What phenomenon describes the complete closure of Na+ channels at their peak?

The phenomenon that describes the complete closure of Na+ channels at their peak is repolarization. During an action potential, when depolarization occurs, Na+ channels open rapidly, allowing sodium ions to flow into the cell. This influx of positive charge causes the inside of the neuron to become more positive. After reaching the peak of the action potential, these sodium channels close completely, stopping further influx of Na+ ions.

Repolarization then follows, during which the membrane potential returns to its resting state. This process is primarily driven by the efflux of potassium ions through K+ channels that open in response to the change in membrane potential. As K+ leaves the cell, the interior becomes less positive, restoring the negative internal environment relative to the outside.

This sequence is vital for the proper functioning of neurons, as it allows for the reset of the membrane potential, preparing it for the next action potential. Hence, the correct answer fundamentally ties to the physiological processes occurring in neurons during the transmission of signals.