synapse /sin″aps, sinaps″/ [Gk, synaptein, to join] , 1. n., the region surrounding the point of contact between two neurons or between a neuron and an effector organ, across which nerve impulses are transmitted through the action of a neurotransmitter, such as acetylcholine or norepinephrine. When an impulse reaches the terminal point of one neuron, it causes the release of the neurotransmitter. The neurotransmitter diffuses across the gap between the two cells to bind with receptors in the other neuron, muscle, or gland, triggering electric changes that either inhibit or continue the transmission of the impulse. Synapses are polarized so that nerve impulses normally travel in only one direction; they are also subject to fatigue, oxygen deficiency, anesthetics, and other chemical agents. Compare ephapse. Kinds include axoaxonic synapse, axodendritic synapse, axodendrosomatic synapse, axosomatic synapse, dendrodendritic synapse. 2. v., to form a synapse or connection between neurons. 3. v., (in genetics) to form a synaptic fusion between homologous chromosomes during meiosis. −synaptic, adj.
