Inhibitory postsynaptic potentials

An Inhibitory Postsynaptic Potential (commonly abbreviated as IPSP) is the change in membrane voltage of a postsynaptic neuron which results from synaptic activation of inhibitory neurotransmitter receptors. The most common inhibitory neurotransmitters in the nervous system are GABA and glycine.

A postsynaptic potential is considered inhibitory, when the resulting change in membrane voltage makes it more difficult for the cell to fire an action potential, lowering the firing rate of the neuron. They are the opposite of excitatory postsynaptic potentials (EPSPs), which result from the flow of positive ions into the cell.

Ionic basis of IPSP
At a typical inhibitory synapse the postsynaptic neural membrane permeability increases for positive potassium (K+) ions and negative chloride (Cl-) ions but not sodium (Na+) ions. This generally causes an influx of Cl- ions and efflux of K+ ions, thereby bringing the membrane potential closer to the equilibrium potential of these ions.

In addition IPSPs may be produced by closure of sodium or calcium channels.