excitatory postsynaptic potential

An excitatory postsynaptic potential (EPSP) is a temporary change in a neuron's membrane polarization that can lead to the firing of a new nerve impulse. When a nerve impulse reaches a synapse, neurotransmitters are released, opening ion channels in the postsynaptic neuron's membrane. The flow of ions through these channels causes depolarization, a decrease in the negative charge inside the neuron. If this depolarization reaches a critical threshold, it triggers an action potential, or nerve impulse.1

The degree of depolarization in an EPSP varies based on ion channel activity. Neurons can integrate multiple EPSPs from different synapses through a process called summation, which can be spatial (simultaneous signals from multiple synapses) or temporal (successive signals from the same synapse). The equivalent of an EPSP at nerve-muscle junctions is called an end-plate potential (EPP).12