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the junction between the processes of two neurons or between a neuron and an effector organ, where neural impulses are transmitted by chemical means. The impulse causes the release of a neurotransmitter (e.g., acetylcholine or norepinephrine) from the presynaptic membrane of the axon terminal. The neurotransmitter molecules diffuse across the synaptic cleft, bind with specific receptors on the postsynaptic membrane, causing depolarization or hyperpolarization of the postsynaptic cell. See also neuron.
axoaxonic synapse one between the axon of one neuron and the axon of another neuron.
axodendritic synapse one between the axon of one neuron and the dendrites of another.
axodendrosomatic synapse one between the axon of one neuron and the dendrites and body of another.
axosomatic synapse one between the axon of one neuron and the body of another.
dendrodendritic synapse one from a dendrite of one cell to a dendrite of another.
electrotonic synapse a special type of gap junction found in tissue such as the myocardium.
syn·aps·es(sin'aps, sĭ-naps'; sy-nap'sez), Avoid mispronouncing the plural of this English word sin-ap'sēz.
The functional membrane-to-membrane contact of the nerve cell with another nerve cell, an effector (muscle or gland) cell, or a sensory receptor cell. The synapse subserves the transmission of nerve impulses, commonly from a variably large (1-12 mcm), 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 synapse occurs. In most cases, the impulse is transmitted by means of a chemical transmitter substance (such as acetylcholine, γ-aminobutyric acid, dopamine, or 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 round or ellipsoid, membrane-bound synaptic vesicles (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 synapse), but in some synapses synaptic vesicles occur on both sides of the synaptic cleft, which suggest the possibility of reciprocal chemical transmission.
[syn- + G. hapto, to clasp]
The junction across which a nerve impulse passes from an axon terminal to a neuron, muscle cell, or gland cell.
intr.v. syn·apsed, syn·apsing, syn·apses
1. To form a synapse.
2. To undergo synapsis.
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 synapse subserves the transmission of nerve impulses, commonly from a club-shaped axon terminal (the presynaptic element) to the circumscript patch of the plasma membrane of the receiving cell (the postsynaptic element) on which the synapse occurs. In most cases, the impulse is transmitted by means of a chemical transmitter substance (such as acetylcholine, gamma-aminobutyric acid, dopamine, norepinephrine) released into a synaptic cleft that separates the presynaptic from the postsynaptic membrane; the transmitter is stored in synaptic vesicles in the presynaptic element. In other synapses, transmission takes place by direct propagation of the bioelectrical potential from the presynaptic to the postsynaptic membrane.
[syn- + G. hapto, to clasp]
synapse(sin'aps) [Gr. synapsis, point of contact]
The space between the junction of two neurons in a neural pathway, where the termination of the axon of one neuron comes into close proximity with the cell body or dendrites of another. The electrical impulse traveling along a presynaptic neuron to the end of its axon releases a chemical neurotransmitter that stimulates or inhibits an electrical impulse in the postsynaptic neuron; synaptic transmission is in one direction only. Synapses are susceptible to fatigue, offer a resistance to the passage of impulses, and are markedly susceptible to the effects of oxygen deficiency, anesthetics, and other agents, including therapeutic drugs and toxic chemicals. Synonym: synapsis (1) See: illustration
The synapse between an axon of one neuron and the dendrites of another.
The synapse between the axon of one neuron and the dendrites and cell body of another.
The synapse between the axon of one neuron and the cell body of another.
synapseThe junctional area between two connected nerves, or between a nerve and the effector organ (a muscle fibre or a gland). Nerve impulses are transmitted across a synapse by means of a chemical NEUROTRANSMITTER such as ACETYLCHOLINE or NORADRENALINE. Synapses allow impulses to pass in one direction only and single brain cells may have more than 15 000 synapses with other cells. This complexity, allowing logical ‘gate’ operation, partly or wholly underlies the computational and storage abilities of the brain.
- the point at which one nerve cell connects with another and at which transmission of an impulse takes place by chemical means. When an impulse arrives at a synapse it causes a synaptic vesicle to move towards the presynaptic membrane. On contacting the membrane it discharges the contained transmitter substance into the synaptic cleft, across which it diffuses to the postsynaptic membrane which it depolarizes. This causes a positive charge to develop (excitory postsynaptic potential -EPSP) because of sodium ions flowing into the post synaptic nerve cell. When the positive charge builds up sufficiently it generates an action potential which is usually unidirectional. See ENDPLATE, MOTOR and Fig. 148 .
- the point of contact of homologous regions of DNA prior to RECOMBINATION, as in the pairing of homologous chromosomes during MEIOSIS.
A connection between nerve cells, by which nervous excitation is transferred from one cell to the other.
The place where a nerve impulse is transmitted from one neuron to another. This transmission is usually mediated by neurotransmitters (e.g. acetylcholine, noradrenaline (norepinephrine), glutamate, etc.) that are released by the presynaptic neuron, then diffuse across the synaptic cleft (about 20-50 nm wide) to bind to receptor sites on the postsynaptic membrane and generate an electrical change in the postsynaptic neuron, which results in either depolarization (excitation) or hyperpolarization (inhibition). This is often referred to as a chemical synapse. There is another type of synapse called an electrotonic synapse (electrical synapse) in which electrical impulses are transmitted via ionic currents from one neuron to another by direct propagation across a gap junction (2-3nm wide). Electrotonic synapses are rare in vertebrates and have been found at only a few central nervous sites. It is estimated that a cortical neuron, for example, makes some 5000-10 000 synapses with surrounding neurons. See neuron; neurotransmitter; receptor potential.
syn·apse, pl. synapses (sin'aps, -ĕz)
Functional membrane-to-membrane contact of nerve cell with another.
[syn- + G. hapto, to clasp]