EPSP

An excitatory postsynaptic potential (EPSP) is a postsynaptic depolarizing event that brings the membrane potential closer to the threshold for firing an action potential. EPSPs occur when an excitatory neurotransmitter released by a presynaptic neuron binds to receptors on the postsynaptic membrane, opening cation channels and allowing positively charged ions to enter the cell.

In the central nervous system, glutamate is the principal excitatory neurotransmitter. The most common receptors mediating EPSPs are AMPA receptors, which produce a rapid, short-lived depolarization by allowing Na+ to enter and K+ to exit. NMDA receptors also contribute to EPSPs; they are voltage-dependent and require depolarization to relieve a Mg2+ block, permitting Ca2+ (and Na+) influx and contributing to longer-lasting depolarization and calcium signaling. The reversal potential for AMPA receptor–mediated currents is near 0 mV.

The magnitude and duration of an EPSP depend on factors such as the electrotonic distance from the synapse to the soma, dendritic properties, and receptor composition. Individual EPSPs are typically a few millivolts at the soma and decay with distance from the synapse. AMPA-mediated EPSPs are fast, peaking within a few milliseconds, while NMDA-mediated components develop more slowly and can persist longer.

Summation allows EPSPs from multiple synapses (temporal summation from rapid successive inputs and spatial summation from inputs at different locations) to bring the postsynaptic neuron to the action potential threshold. EPSPs are contrasted with inhibitory postsynaptic potentials (IPSPs), which hyperpolarize or stabilize the membrane potential.

Role in neural function: EPSPs enable synaptic integration and information transfer, and NMDA receptor involvement links synaptic activity to plasticity mechanisms such as long-term potentiation.