Synapses, Neurotransmitters and Receptor Channels
University College London, UK
Synapses are regions of contact between nerve cells specialized to generate, transmit and receive chemical signals that mediate fast information transfer in the brain. Transmission occurs when the presynaptic terminal releases neurotransmitters which activate receptor channels in the membrane of the postsynaptic cell. The identity of the presynaptic neurotransmitter, and... read morethe type of postsynaptic ligand-gated receptor channels present are both therefore of critical importance in shaping the signal that is transferred between nerve cells. In this process, the ligand-gated receptor channel represents the fundamental piece of molecular hardware that converts neurotransmitter binding into a subtle postsynaptic electrical event.
While synaptic transmission is fundamental to all fast information transfer between nerve cells in the brain, and between central neurons and peripheral structures, its efficiency at any given synapse is constantly changing in response to various factors. These changes in efficiency play a critical role in the functioning of the nervous system in such processes as learning and memory. Changes can occur in the synaptic structures present, in the release process itself, and in the properties of postsynaptic receptors and associated proteins. However, not all changes are beneficial and ligand-gated receptor channels are involved not only in normal transmission of signals but also a wide variety of neurological disorders and defects.
Early studies on ligand-gated channels (such as those at acetylcholine and glutamate-mediated receptors in frog and invertebrate nerve-muscle synapses) seemed to suggest that neurotransmitters activate a population of receptors with homogeneous channel properties. However, more recent work on mammalian synapses has elucidated an altogether more versatile picture with a much higher degree of heterogeneity. The discovery of this heterogeneity in receptor-channel properties is providing important information concerning a major issue in our understanding of synaptic transmission - namely, how transmitters can generate such enormous diversity in signalling between nerve cells.