Medical Definition of active zone
: a specialized area on the presynaptic membrane of a nerve cell where synaptic vesicles cluster and are released into the synaptic cleft At the site of contact, the presynaptic plasma membrane develops into an active zone, which is where synaptic vesicles undergo exocytosis and release neurotransmitters into the synaptic cleft.—Thomas Biederer et al., Science, 30 Aug. 2002
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