Synapse

Synapse A chemical synapse consists of a neuronal presynaptic terminal, a synaptic cleft and a postsynaptic membrane with associated receptor proteins. The chemical synapse is highly developed in the CNS. It conducts the signal only one way, and has a synaptic delay. The presynaptic axon terminal typically broadens to form a bouton terminaux (presynaptic terminal). The action potential, which originates in the CNS, depolarises the axon membrane by an influx of Na+. Repolarization follows rapidly by selective K+-efflux When the action potential reaches the presynaptic membrane, Ca2+ enters the terminal through voltage-gated Ca2+-channels. Vesicles containing transmitter, fuse with the presynaptic membrane and release their contents of acetylcholine into the synaptic cleft causing exocytosis. Acetylcholine, diffuses across the synaptic cleft and binds to specific receptors, which are located into the postsynaptic membrane. This ligand binding elicits a transient opening of pores, which are specifically permeable to small cations. The synaptic cleft of a chemical synapse is about 30 nm. The ACh-receptor opens and allows influx of Na+, whereby the membrane depolarizes and an action potential is generated which propagates along the length of the postganglionic axon. This is an appropriate response of the postsynaptic cell to the received signal. potential, synaptic, postsynaptic, membrane, presynaptic, axon, action, na, voltage-gated, terminal, synapse, summation, cleft, cell, receptors, potentials, pores, influx, hillock, chemical, acetylcholine, transmitter, through, summate, specific, signal, results, post-synaptic, occurs, molecules, involved, inputs, excitatory, epsps, epsp