Search results
Results from the WOW.Com Content Network
The refractory period of a neuron is the time in which a nerve cell is unable to fire an action potential (nerve impulse). Two subsets exist in terms of neurons: absolute refractory period and relative refractory period. The first describes the inability to send a new impulse when sodium channels preceding this impulse are inactivated.
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.
Because voltage-gated Na + channels are inactivated at the peak of the depolarization, they cannot be opened again for a brief time (absolute refractory period). Because of this, positive ions spreading back toward previously opened channels has no effect.
Absolute refractory period: Spans from the depolarization phase to the initial repolarization phase of the action potential. Relative refractory period : Spans from the late repolarization phase to the hyperpolarization phase of the action potential.
Because voltage-gated Na + channels are inactivated at the peak of the depolarization, they cannot be opened again for a brief time—the absolute refractory period. Because of this, depolarization spreading back toward previously opened channels has no effect.
Immediately after an action potential generates, the neuron cannot immediately generate another action potential; this is the absolute refractory period. At this moment, the sodium channels are inactivated and remain closed, whereas the potassium channels are still open.
The absolute refractory period is primarily a consequence of the inactivation of voltage-gated sodium channels. These channels are responsible for the rapid influx of sodium ions that depolarize the neuron’s membrane and generate an action potential.
The absolute refractory period is followed by a relative refractory period, during which a strong stimulation may trigger a new action potential. The absolute and relative refractory periods are displayed in Figure 1 (above) and Figure 2 (below).
In human sexuality, the refractory period is usually the recovery phase after orgasm, during which it is physiologically impossible for males to have additional orgasms. [1] [2] This phase begins immediately after ejaculation, and lasts until the excitement phase of the human sexual response cycle begins anew with low-level response.
Two types of refractory periods are usually defined: an absolute refractory period and a relative refractory period (Fig. 19.5). The absolute refractory period denotes the interval during which a second AP cannot be elicited, regardless of the intensity of the applied stimulus.