Synapse
Say it: SIN-aps
A synapse is the junction where a neuron passes a signal to another cell, usually by releasing a neurotransmitter across a narrow gap.
Also: synapses, synaptic junction
Definition
What is a synapse?
A synapse is the point at which a neuron passes signals to a target cell, which may be another neuron, a muscle fiber or a gland cell. At a chemical synapse, the sending (presynaptic) cell and the receiving (postsynaptic) cell are separated by a very narrow gap called the synaptic cleft. At an electrical synapse, the two cells are joined directly by gap junctions, so ions pass straight from one to the other almost instantly.
At a chemical synapse, an action potential reaching the axon terminal opens voltage-gated calcium channels. The incoming calcium makes vesicles fuse with the membrane and empty neurotransmitter into the cleft. The transmitter binds specific receptors on the postsynaptic membrane and produces an excitatory or an inhibitory response. The signal stops when the transmitter diffuses away, is broken down by an enzyme, or is taken back up by the presynaptic cell or nearby glia. This makes chemical transmission one-way and slightly delayed.
Many drugs and toxins act at synapses, and synapses can grow stronger or weaker with use, a property called synaptic plasticity that underlies learning. The neuromuscular junction, where a motor neuron triggers muscle contraction, is the classic example in physiology courses.
Word parts
Where does the word “synapse” come from?
- syn-
- togetherGreek syn
- -apse
- to fasten or claspGreek haptein, giving synapsis (a joining)
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Related
Terms that go with it
- NeurotransmitterA neurotransmitter is a chemical messenger that a neuron releases at a synapse to excite or inhibit a target neuron, muscle cell or gland cell.
- NeuronA neuron is a nerve cell, the basic signaling unit of the nervous system, which receives information and passes it on as electrical and chemical signals.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- Action potentialAn action potential is a brief, all-or-none reversal of the voltage across a nerve or muscle cell membrane that travels along the cell as a signal.
- AcetylcholineAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
- DendriteA dendrite is one of the short, branching extensions of a neuron that receive signals from other cells and carry them toward the cell body.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 12.5 Communication Between Neurons
- OpenStax Biology 2e, 35.2 How Neurons Communicate
- NCI Dictionary of Cancer Terms: synapse
- NCBI MeSH: Synapses
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