synapse

/sin"aps, si naps"/, n., v., synapsed, synapsing. Physiol.
n.
1. a region where nerve impulses are transmitted and received, encompassing the axon terminal of a neuron that releases neurotransmitters in response to an impulse, an extremely small gap across which the neurotransmitters travel, and the adjacent membrane of an axon, dendrite, or muscle or gland cell with the appropriate receptor molecules for picking up the neurotransmitters.
v.i.
2. Cell Biol.; Physiol. to form a synapse or a synapsis.
[1895-1900; back formation from synapses, pl. of SYNAPSIS]

* * *

Site of transmission of electric nerve impulses between two nerve cells or between a nerve cell and a gland or muscle cell.

At chemical synapses, impulses are transmitted across microscopic spaces via chemical substances called neurotransmitters. In electric synapses, direct communication between nerve cells whose membranes are fused is possible because ions flow between the cells through channels. Electric synapses are found mainly in invertebrates and lower vertebrates; they transmit messages faster than chemical synapses. Chemical transmission seems to have evolved in large, complex vertebrate nervous systems, in which multiple messages must be transmitted over long distances.

* * *

also called  neuronal junction 

      the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction.

 At a chemical synapse each ending, or terminal, of a nerve fibre (presynaptic fibre) swells to form a knoblike structure that is separated from the fibre of an adjacent neuron, called a postsynaptic fibre, by a microscopic space called the synaptic cleft. The typical synaptic cleft is about 0.02 micron wide. The arrival of a nerve impulse at the presynaptic terminals causes the movement toward the presynaptic membrane of membrane-bound sacs, or synaptic vesicles, which fuse with the membrane and release a chemical substance called a neurotransmitter. This substance transmits the nerve impulse to the postsynaptic fibre by diffusing across the synaptic cleft and binding to receptor molecules on the postsynaptic membrane. The chemical binding action alters the shape of the receptors, initiating a series of reactions that open channel-shaped protein molecules. Electrically charged ions then flow through the channels into or out of the neuron. This sudden shift of electric charge across the postsynaptic membrane changes the electric polarization of the membrane, producing the postsynaptic potential, or PSP. If the net flow of positively charged ions into the cell is large enough, then the PSP is excitatory; that is, it can lead to the generation of a new nerve impulse, called an action potential.

      Once they have been released and have bound to postsynaptic receptors, neurotransmitter molecules are immediately deactivated by enzymes in the synaptic cleft; they are also taken up by receptors in the presynaptic membrane and recycled. This process causes a series of brief transmission events, each one taking place in only 0.5 to 4.0 milliseconds.

      A single neurotransmitter may elicit different responses from different receptors. For example, norepinephrine, a common neurotransmitter in the autonomic nervous system, binds to some receptors that excite nervous transmission and to others that inhibit it. The membrane of a postsynaptic fibre has many different kinds of receptors, and some presynaptic terminals release more than one type of neurotransmitter. Also, each postsynaptic fibre may form hundreds of competing synapses with many neurons. These variables account for the complex responses of the nervous system to any given stimulus. The synapse, with its neurotransmitter, acts as a physiological valve, directing the conduction of nerve impulses in regular circuits and preventing random or chaotic stimulation of nerves.

      Electric synapses allow direct communications between neurons whose membranes are fused by permitting ions to flow between the cells through channels called gap junctions. Found in invertebrates (invertebrate) and lower vertebrates (vertebrate), gap junctions allow faster synaptic transmission as well as the synchronization of entire groups of neurons. Gap junctions are also found in the human body, most often between cells in most organs and between glial cells of the nervous system. Chemical transmission seems to have evolved in large and complex vertebrate nervous systems, where transmission of multiple messages over longer distances is required.

* * *


Universalium. 2010.

Look at other dictionaries:

  • synapse — [ sinaps ] n. f. • 1897; angl. synapsis; gr. sunapsis « liaison; point de jonction » 1 ♦ Anat. Région de contact de deux neurones. Synapse neuromusculaire : contact entre un neurone et le muscle qu il innerve. 2 ♦ (1924; synapsis 1904) Biol.… …   Encyclopédie Universelle

  • synapse — junction between two nerve cells, 1899, from Gk. synapsis conjunction, from synaptein to clasp, from syn together + haptein to fasten. Related to APSE (Cf. apse). Introduced by English physiologist Sir Michael Foster (1836 1907) at the suggestion …   Etymology dictionary

  • synapse —  Synapse  Синапс   Конъюгация хромосом, попарное временное сближение гомологичных хромосом, во время которого между ними может произойти обмен гомологичными участками. На этой стадии хромосомы под влиянием разных воздействий легко сжимаются в… …   Толковый англо-русский словарь по нанотехнологии. - М.

  • synapse — ► NOUN ▪ a gap between two nerve cells, across which impulses are conducted through the agency of a neurotransmitter. DERIVATIVES synaptic adjective. ORIGIN Greek sunapsis, from sun together + hapsis joining …   English terms dictionary

  • synapse — [sin′aps΄, si naps′] n. [ModL synapsis: see SYNAPSIS] the minute space between a nerve cell and another nerve cell, a muscle cell, etc., through which nerve impulses are transmitted from one to the other …   English World dictionary

  • Synapse — Pour les articles homonymes, voir synapse (homonymie). Synapse entre deux neurones La synapse (du grec. syn = ensemble; haptein = toucher, saisir; c est à dire connexi …   Wikipédia en Français

  • Synapse — Synapsen (Einzahl die Synapse, von gr. σύν, syn = zusammen, ἅπτειν, haptein = ergreifen, fassen, tasten) sind Kontaktstellen zwischen Nervenzellen und anderen Zellen (wie Sinnes , Muskel oder Drüsenzellen) oder zwischen Nervenzellen untereinander …   Deutsch Wikipedia

  • synapse — A connection between excitable cells, by which an excitation is conveyed from one to the other. (1) Chemical synapse: one in which an action potential causes the exocytosis of neurotransmitter from the presynaptic cell, which diffuses across the… …   Dictionary of molecular biology

  • Synapse — 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… …   Medical dictionary

  • Synapse — ◆ Syn|ạp|se 〈f. 19; Biochem.〉 Kontaktstelle der Neuronen [<grch. synapsis „eng verbunden“] ◆ Die Buchstabenfolge syn|a... bzw. syn|ä... kann in Fremdwörtern auch sy|na... bzw. sy|nä... getrennt werden. * * * Sy|n|ạp|se, die; , n [griech.… …   Universal-Lexikon

  • Synapse —    This is the gap between two neurons, where the nerve impulse is transmitted by a chemical neurotransmitter, such as acetylcholine. Molecules of the neurotransmitter are released into the synapse by the end bulb (axon terminal) of the… …   Historical dictionary of Psychiatry

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.