<P> In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential . This temporary depolarization of postsynaptic membrane potential, caused by the flow of positively charged ions into the postsynaptic cell, is a result of opening ligand - gated ion channels . These are the opposite of inhibitory postsynaptic potentials (IPSPs), which usually result from the flow of negative ions into the cell or positive ions out of the cell . EPSPs can also result from a decrease in outgoing positive charges, while IPSPs are sometimes caused by an increase in positive charge outflow . The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC). </P> <P> EPSPs, like IPSPs, are graded (i.e. they have an additive effect). When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect is the sum of the individual EPSPs . Larger EPSPs result in greater membrane depolarization and thus increase the likelihood that the postsynaptic cell reaches the threshold for firing an action potential . </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (February 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Action potentials and excitatory postsynaptic potentials (epsps) are similar in that both