Mechanism of synaptic transmission
A synapse is a junction through which a neuron passes information to another neuron. Presynaptic terminals contain chemical neurotransmitters enclosed in small spherical intramembrane structures called synaptic vesicles. When an action potential, a wave of electrical excitation, reaches the presynaptic terminal, the membranes of some synaptic vesicles fuse with the membrane of the presynaptic terminal, thereby opening the vesicles in a process known as exocytosis, which releases their neurotransmitters into the synaptic cleft, the space between the pre and postsynaptic cell membranes. The neurotransmitter diffuses into the cleft and binds to receptors located on the postsynaptic membranes. The fused membranes of synaptic vesicles are retrieved in presynaptic terminals in a procedure called endocytosis, after which they are reused. Maintaining the balance between the amount of exocytosed vesicles and endocytosed vesicles is essential for continuous neurotransmission.
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