Refractory Period

For a moment following the passage of a nerve impulse, an ordinary stimulus will not be able to trigger another impulse on a nerve fiber.

This brief period of time, the refractory period, has two parts-.

During the absolute refractory period, which lasts about 1/2500 of a second, the fiber's membrane is changing in sodium permeability and cannot be stimulated.

This is followed by a relative refractory period, during which the membrane is reestablishing its resting potential.

While the membrane is in this relative refractory period, even though polarization is incomplete, an impulse may be triggered by a stimulus of high intensity.