<prompt> Influx of which of the following ion is responsible for IPSP inhibitory postsynaptic potential: March 2005Potassium ionChloride ionCalcium ionSodium ion  <response>: Ans. B: Chloride ion Sodium ion Despite their name, some neurotransmitters inhibit the transmission of nerve impulses. They do this by opening Chloride channels andor Potassium channels in the plasma membrane. In each case, opening of the channels increases the membrane potential by Letting negatively-charged chloride ions C1 in and Positively-charged potassium ions K out This hyperpolarization is called an inhibitory postsynaptic potential IPSP. Although the threshold voltage of the cell is unchanged, it now requires a stronger excitatory stimulus to reach threshold. Example: Gamma amino butyric acid GABA. This neurotransmitter is found in the brain and inhibits nerve transmission by both mechanisms: Binding to GABAA receptors opens chloride channels in the neuron. Binding to GABAB receptors opens potassium channels. 