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Excitatory postsynaptic potential
In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the 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).
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.
==Overview==
EPSPs in living cells are caused chemically. When an active presynaptic cell releases neurotransmitters into the synapse, some of them bind to 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 receptors). 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.
The Excitatory graphs to the right need amendment as the Threshold Potential is -55mV so the so-called failure would actually lead to AP. The scale just needs altering to something more reasonable.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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