Chemical Synapses Essay Example | Topics and Well Written Essays - 500 words

Chemical Synapses - Essay Example The process that must occur in the presynaptic axon is a series of events that lead to release of a neurotransmitter. An action potential in the presynaptic cell causes Ca2+ channels to open. An influx of Ca2+ into the presynaptic terminal causes the neurotransmitter, which is stored in synaptic vesicles, to be released by exocytosis. The neurotransmitter diffuses across the synaptic cleft, binds to receptors on the postsynaptic membrane, and produces a change in membrane potential on the postsynaptic cell. The change in membrane potential on the postsynaptic cell membrane can be either excitatory or inhibitory, depending on the nature of the neurotransmitter released from the presynaptic nerve terminal. If the neurotransmitter is excitatory, it causes depolarization of the postsynaptic cell; if the neurotransmitter is inhibitory, it causes hyperpolarization of the postsynaptic cell. Local currents depolarize each adjacent region to threshold. Finally, the presynaptic terminal is depolarized, and this depolarization causes voltage-gated Ca2+ channels in the presynaptic membrane to open. When these Ca2+ channels open, the Ca2+ permeability of the presynaptic terminal increases, and Ca2+ flows into the terminal down its electrochemical gradient. Ca2+ uptake into the terminal causes release of the neurotransmitter acetylcholine (ACh), which has been previously synthesized and stored in synaptic vesicles. To release ACh, the synaptic vesicles fuse with the plasma membrane and empty their contents into the synaptic cleft by exocytosis. ACh is formed from acetyl coenzyme A (Acetyl CoA) and choline by the action of the enzyme choline acetyltransferase.