Refractory Period. Image created at BYU-Idaho, Fall 2015
Another concept to be discussed is the refractory period. By definition, the refractory period is the amount of time during which a cell is incapable of repeating another action potential after one has been initiated. There are two types of refractory periods: The absolute refractory period, which is the interval of time during which a second action potential cannot be initiated, no matter how large a stimulus is repeatedly applied. Second, the relative refractory period, which is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before. Refractory periods are caused by the inactivation gate of the voltage-gated Na+ channel. Once inactivated, the Na+ channel cannot respond to another stimulus until the activation and inactivation gates are reset.
Here is a video to help with understanding: