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In the nervous system, a synapse [1] is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending on the mechanism of signal transmission between neurons.
The synapse is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. At gap junctions, such cells approach within about 3.8 nm of each other, [1] a much shorter distance than the 20- to 40-nanometer distance that separates cells at a chemical synapse. [2]
The neuromuscular junction (NMJ) is the most well-characterized synapse in that it provides a simple and accessible structure that allows for easy manipulation and observation. The synapse itself is composed of three cells: the motor neuron , the myofiber , and the Schwann cell .
Mutants in rab-3 and munc-18 alter vesicle docking or vesicle organization at release sites, but they do not completely disrupt docking. [14] SNARE proteins, now also appear to be involved in the docking step of the cycle. [15] 4. Priming. After the synaptic vesicles initially dock, they must be primed before they can begin fusion.
Axon terminals are specialized to release neurotransmitters very rapidly by exocytosis. [1] Neurotransmitter molecules are packaged into synaptic vesicles called quanta that cluster beneath the axon terminal membrane on the presynaptic side (A) of a synapse.
An electrical synapse is an electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic cells, known as a gap junction. At gap junctions, cells approach within about 3.5 nm of each other, rather than the 20 to 40 nm distance that separates cells at chemical synapses.
Structure of a typical chemical synapse A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse . The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell .
[3] Chemical synaptic transmission is the transfer of neurotransmitters or neuropeptides from a presynaptic axon to a postsynaptic dendrite. [3] Unlike an electrical synapse, the chemical synapses are separated by a space called the synaptic cleft, typically measured between 15 and 25 nm. Transmission of an excitatory signal involves several ...