Refractory period
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Refractory period in biology
Biologically, a refractory period is the amount of time it takes for an excitable membrane to be stimulated and then be ready for stimulus again.
Action potentials in Neurons
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The refractory period in a neuron occurs after an action potential. The action potential ends when voltage-gated ion channels allow positively charged potassium ions to leave the cell, between the 2nd and 3rd millisecond after the action potential. During this repolarization period when the potassium ion-channels are open, it is impossible to have another action potential. As a result, this is known as the absolute refractory period.
The ion channels cause an 'overshoot' (between the 3rd and 4th milliseconds) - the voltage across the membrane becomes much more negative than usual. During this period, it is possible to have an action potential, but much harder than normal. This is known as the relative refractory period.
Refractory period in sex
In sexual intercourse, the refractory period is a recovery phase after male ejaculation during which it is physiologically impossible for almost all men to experience sustained erection and additional ejaculations or orgasms. The penis may be hypersensitive and further sexual stimulation may even feel painful during this time frame.
The refractory period varies widely between individuals, ranging from minutes to hours. An increased infusion of the hormone oxytocin during ejaculation is believed to be chiefly responsible for the refractory period and the amount by which oxytocin is increased may affect the length of each refractory period.
Unlike men, women do not experience a refractory period immediately after orgasm and in many cases are capable of attaining additional, multiple orgasms through further stimulation.
Refractory period in cardiac physiology
In cardiac physiology, the refractory period is the time between heart contractions. Problems with the refractory period in the major pathways of the heart are known as heart block.