APA Dictionary of Psychology

a group of proteins forming a channel that spans a cell membrane, allowing the passage of ions between the extracellular environment and the cytoplasm of the cell. Ion channels are selective; allow passage of ions of a particular chemical nature, size, or electrostatic charge; and may be ungated (i.e., always open) or gated, opening and closing in response to chemical, electrical, or mechanical signals (see ligand-gated ion channel; voltage-gated ion channel). Ion channels are important in the transmission of neural signals between neurons at a synapse. The opening of sodium channels in the membrane of a postsynaptic neuron permits an influx of sodium ions (Na⁺) into the neuron, which produces an excitatory postsynaptic potential. The opening of potassium channels or chloride channels allows potassium ions (K⁺) to leave the postsynaptic neuron or chloride ions (Cl^–) to enter it, either of which produces an inhibitory postsynaptic potential. See also calcium channel.