The Postsynaptic Neuron I: Actions of Neurotransmitters

Abstract

Neurotransmitter released from the presynaptic neuron diffuses across the synaptic gap and combines with specific receptor molecules located in the membrane of the postsynaptic cell. (Some transmitters, upon release, combine with receptors — autoreceptors — on the presynaptic neuron, see Chapter 7.) The combination of transmitter with receptor leads to changes in the postsynaptic cell that can be of two general types, either affecting chemically gated (ligand-gated) ion channels or affecting the metabolism of the cell. Once the appropriate postsynaptic response has occurred it is obviously important that the system should be reset to allow further actions to take place. The transmitter is usually released from its combination with the receptor and removed from the synaptic cleft. Removal of transmitter may be achieved by re-uptake into the terminals of the presynaptic neuron, by enzymic degradation (which may be combined with re-uptake) or by diffusion away from the cleft (see Chapter 7).