the stage in action potential that immediately follows depolarization is known as
Refractory period (physiology) After initiation of an action potential, the refractory period is defined two ways: The absolute refractory period coincides with nearly the entire duration of the action potential. In neurons, it is caused by the inactivation of the Na+ channels that originally opened to depolarize the membrane. These channels remain inactivated until the membrane hyperpolarizes. The channels then close, de-inactivate, and regain their ability to open in response to stimulus.