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An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential. [1] The opposite of an inhibitory postsynaptic potential is an excitatory postsynaptic potential (EPSP), which is a synaptic potential that makes a postsynaptic neuron more likely to generate an action potential.
This means a single EPSP/IPSP is typically not enough to trigger an action potential. The two ways that synaptic potentials can add up to potentially form an action potential are spatial summation and temporal summation. [5]
Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse.Postsynaptic potentials are graded potentials, and should not be confused with action potentials although their function is to initiate or inhibit action potentials.
The neurotransmitter most often associated with EPSPs is the amino acid glutamate, and is the main excitatory neurotransmitter in the central nervous system of vertebrates. [2]
The effect of these two options is the hyperpolarization of the postsynaptic cell, or IPSP. Summation with other IPSPs and contrasting EPSPs determines whether the postsynaptic potential will reach threshold and cause an action potential to fire in the postsynaptic neuron.
If an IPSP overlaps with an EPSP, the IPSP can in many cases prevent the neuron from firing an action potential. In this way, the output of a neuron may depend on the input of many different neurons, each of which may have a different degree of influence, depending on the strength and type of synapse with that neuron.
On the other hand, if the reversal potential of the receptor to which the neurotransmitter binds is lower than the threshold potential, an inhibitory postsynaptic potential will occur (IPSP). [ 4 ]
Shunting inhibition, also known as divisive inhibition, is a form of postsynaptic potential inhibition that can be represented mathematically as reducing the excitatory potential by division, rather than linear subtraction. [1]