“post synaptic potential”

: increased negativity of the membrane potential of a neuron on the postsynaptic side of a nerve synapse that is caused by a neurotransmitter (as gamma-aminobutyric acid) which renders the membrane selectively permeable to potassium and chloride ions on the inside but not to sodium ions on the outside and that tends to inhibit the neuron since an added increase in potential in the positive direction is needed for excitation —abbreviation IPSP