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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 strength of a synapse has been defined by Bernard Katz as the product of (presynaptic) release probability pr, quantal size q (the postsynaptic response to the release of a single neurotransmitter vesicle, a 'quantum'), and n, the number of release sites. "Unitary connection" usually refers to an unknown number of individual synapses ...
In immunology, an immunological synapse (or immune synapse) is the interface between an antigen-presenting cell or target cell and a lymphocyte such as a T cell, B cell, or natural killer cell. The interface was originally named after the neuronal synapse , with which it shares the main structural pattern. [ 1 ]
Once at the synapse, synaptic vesicles are loaded with a neurotransmitter. Loading of transmitter is an active process requiring a neurotransmitter transporter and a proton pump ATPase that provides an electrochemical gradient. These transporters are selective for different classes of transmitters.
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.
An excitatory synapse is a synapse in which an action potential in a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell. Neurons form networks through which nerve impulses travels, each neuron often making numerous connections with other cells of neurons.
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 .
This synapse has been described as the largest in the brain. [10] The related endbulb of Held is also a large axon terminal synapse (15–30 μm in diameter) found in another auditory brainstem structure, namely the anteroventral cochlear nucleus (AVCN). [11] As with the calyces, these synapses promote fast, efficient information transfer.