Postsynaptic Potential

a relatively brief oscillation of membrane potential, generally several dozen milliseconds in duration, and occasionally lasting for seconds. The oscillation results from the action of a mediator on the postsynaptic membrane of a nerve, muscle, or glandular cell. The amplitude of the postsynaptic potential varies with the quantity of the mediator released. By interacting with the specific receptors of a postsynaptic membrane, mediators increase the membrane’s permeability to certain ions, which enter or leave the cell according to an electrochemical gradient. When this leads to a decrease in the difference in potentials between the internal and external sides of a membrane (depolarization), the postsynaptic potential is excitatory.

Inhibitory postsynaptic potential is manifested by hyperpolar-ization of the cell owing to the action of the inhibitory mediator. A nerve cell usually has a large number of synaptic entrances and the incoming signals are summated algebraically. Excitatory postsynaptic potential increases and inhibitory postsynaptic potential decreases the frequency of the discharges in cells that spontaneously generate action potential. In silent cells, excitatory postsynaptic potential may cause a solitary or group discharge; the inhibitory postsynaptic potential arising at the same time may block this effect. Thus, postsynaptic potential controls the excitability of nerve cells.