Synaptic cleft

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Definition

Space of about 15-50 nm between the axolemma of the presynaptic element and the postsynaptic surface.

Synaptic clefts are found at the site of a chemical synapses, and separate the presynaptic from the postsynaptic membranes. The transmitter substance is stored in quantal form in vesicles in the presynaptic element and then released into the synaptic cleft which they must traverse to reach the postsynaptic membrane.

Some enzymes that inactivate neurotransmitters are found in the synaptic cleft, including acetylcholinesterase (which inactivates acytelcholine, ACh) and catechol-O-methyl transferase (COMT) (which inactivates catecholamines).

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