Editing Excitatory postsynaptic potential (section)

{{Short description|Electrical signal encouraging a neuron to fire}}
[[Image:Synapse diag6.png|thumb|300px| This single EPSP does not sufficiently depolarize the membrane to generate an action potential.]]
[[Image:Synapse diag5.png|thumb|300px|The summation of these three EPSPs generates an action potential.]]
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 [[ion]]s into the postsynaptic cell, is a result of opening [[ligand-gated ion channel]]s. These are the opposite of [[inhibitory postsynaptic potential]]s (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''').

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]].


{{Unreferenced section|date=February 2015}}
EPSPs in living cells are caused chemically.  When an active presynaptic cell releases [[neurotransmitter]]s into the synapse, some of them bind to [[neurotransmitter receptor|receptors]] on the postsynaptic cell. Many of these receptors contain an [[ion channel]] capable of passing positively charged ions either into or out of the cell (such receptors are called [[ionotropic receptor]]s). At excitatory synapses, the ion channel typically allows sodium into the cell, generating an [[excitatory postsynaptic current]]. This depolarizing current causes an increase in membrane potential, the EPSP.<ref>Takagi, Hiroshi. “Roles of Ion Channels in EPSP Integration at Neuronal Dendrites.” Neuroscience Research, vol. 37, no. 3, 2000, pp. 167–171., doi:10.1016/s0168-0102(00)00120-6.
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