synapse



synapse defined in 1951 year

synapse - synapse;
synapse - The nervous system of all animals contains immense numbers of distinct nerve-cells which touch each other only at certain places, synapses. There is no continuity between the nerve-cells at these places. Stimulation of one nerve-cell by another is probably confined to the synapses. A synapse is commonly formed by contact of the tip of a terminal banch of the axon belonging to one nerve-cell with the cell-body or with a dendrite of the other nerve-cell. Each axon (unless it is of a motor-fibre) usually has several synapses with each of several other nerve-cells; and each cell-body plus dendrites (unless it is a sensory-cell) has synapses with several nerve-fibres. The cell-body of a large vertebrate motor nerve-cell may bear several hundred or thousand synapses. An impulse, when it reaches a synapse, has to stimulate the next nerve-cell if it is to produce any further effect. This stimulation takes an appreciable time to occur (synaptic delay). Such stimulation may fail to occur if the impulse arrives from the wrong direction, since most synapses transmit only in one direction (from pre-synaptic side to post-synaptic side); thus sensory nerve-cells cannot usually be stimulated across synapses in the central nervous system. Furthermore the stimulation across a synapse may fail to produce an impulse in the nerve-cell receiving it, causing only a transitory rise in responsiveness. (See also: Summation, Facilitation.) Through the operation of summation synapses are highly flexible interconnections. In these animals which have a C.N.S. most synapses are located there.

near synapse in Knolik


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