- The point of connection usually between two nerve cells. Specifically, a synapse is a specialized junction at which a nerve cell (a neuron) communicates with a target cell. The neuron releases a chemical transmitter (a neurotransmitter) that diffuses across a small gap and activates specific specialized sites called receptors situated on the target cell. The target cell may be another neuron, or a specialized region of a muscle cell or a secretory cell (a cell than can make and secrete a substance). Neurons can also communicate through direct electrical connections (electrical synapses). Etymology: The term "synapse" was coined in 1897 by the English physiologist Charles Sherrington, with some help from classical scholars of his acquaintance. They fashioned the word from the Greek word "synaptein" meaning to fasten together. "Synaptein" is combined from the Greek "syn-", together and "haptein" meaning to fasten or bind. (From "haptein" comes the immunologic term "hapten.") History: Sir Charles Scott Sherrington (1857-1952) was a highly influential figure in the development not only of neurophysiology (the intersection between neurology and physiology) but also that of clinical neurology and neurosurgery ("brain surgery"). He worked at Oxford University and is well remembered for the research he did into how nerves work and how they work together. Aside from the synapse, he also coined other useful terms including "neuron" for the nerve cell itself. Sherrington shared the Nobel Prize in Medicine or Physiology in 1932 with Lord Edgar Douglas Adrian of Cambridge University for "their discoveries regarding the functions of neurons."
* * *The functional membrane-to-membrane contact of the nerve cell with another nerve cell, an effector (muscle, gland) cell, or a sensory receptor cell. The s. subserves the transmission of nerve impulses, commonly from a variably large (1–12 μm), generally knob-shaped or club-shaped axon terminal (the presynaptic element) to the circumscript patch of the receiving cell's plasma membrane (the postsynaptic element) on which the s. occurs. In most cases the impulse is transmitted by means of a chemical transmitter substance (such as acetylcholine, γ-aminobutyric acid, dopamine, norepinephrine) released into a synaptic cleft (15–50 nm wide) that separates the presynaptic from the postsynaptic membrane; the transmitter is stored in quantal form in synaptic vesicles: round or ellipsoid, membrane-bound vacuoles (10–50 nm in diameter) in the presynaptic element. In other synapses transmission takes place by direct propagation of the bioelectrical potential from the presynaptic to the postsynaptic membrane; in such electrotonic synapses (“gap junctions”), the synaptic cleft is no more than about 2 nm wide. In most cases, synaptic transmission takes place in only one direction (“dynamic polarity” of the s.), but in some synapses synaptic vesicles occur on both sides of the synaptic cleft, suggesting the possibility of reciprocal chemical transmission. [syn- + G. hapto, to clasp]- axoaxonic s. the synaptic junction between an axon terminal of one neuron and either the initial axon segment or an axon terminal of another nerve cell.- axodendritic s. the synaptic contact between an axon terminal of one nerve cell and a dendrite of another nerve cell.- axosomatic s. the synaptic junction of an axon terminal of one nerve cell to the cell body of another nerve cell. SYN: pericorpuscular s..- pericorpuscular s. SYN: axosomatic s..
* * *syn·apse 'sin-.apsalso sə-'naps, chiefly Brit 'sī-.naps n1) the place at which a nervous impulse passes from one neuron to another2) SYNAPSISsynapse vi, syn·apsed; syn·aps·ing to form a synapse or come together in synapsis
* * *n.the minute gap across which nerve impulse pass from one neurone to the next, at the end of a nerve fibre. Reaching a synapse, an impulse causes the release of a neurotransmitter, which diffuses across the gap and triggers an electrical impulse in the next neurone. Some brain cells have more than 15,000 synapses. See also neuromuscular junction.
* * *syn·apse (sinґaps) [Gr. synapsis a conjunction, connection] the site of functional apposition between neurons, at which an impulse is transmitted from one neuron to another, usually by a chemical neurotransmitter (e.g., acetylcholine, norepinephrine, etc.) released by the axon terminal of the excited (presynaptic) cell. The neurotransmitter diffuses across the synaptic cleft to bind with receptors on the postsynaptic cell membrane, and thereby effects electrical changes in the postsynaptic cell which result in depolarization (excitation) or hyperpolarization (inhibition). Synapses also occur at sites of apposition between nerve endings and effector organs (e.g., the neuromuscular junction). A few synapses in the central nervous system are electrical synapses (q.v.). In official terminology called synapsis.
Diagram of three synapses. Nerve impulse is indicated by arrows, showing that the direction of passage is from the terminal arborization (TA) or nerve endings of the axon of one neuron to the dendrites (D) of another neuron.
Medical dictionary. 2011.