<P> In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron . </P> <P> Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine . The word "synapse"--from the Greek synapsis (συνάψις), meaning "conjunction", in turn from συνάπτεὶν (συν ("together") and ἅπτειν ("to fasten"))--was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster's Textbook of Physiology . Sherrington struggled to find a good term that emphasized a union between two separate elements, and the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall, a friend of Michael Foster . Some authors generalize the concept of the synapse to include the communication from a neuron to any other cell type, such as to a motor cell, although such non-neuronal contacts may be referred to as junctions (a historically older term). </P> <P> Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so . At a synapse, the plasma membrane of the signal - passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell . Both the presynaptic and postsynaptic sites contain extensive arrays of a molecular machinery that link the two membranes together and carry out the signaling process . In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma . Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission . Synapses (at least chemical synapses) are stabilized in position by synaptic adhesion molecules (SAMs) projecting from both the pre - and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses . </P> <P> There are two fundamentally different types of synapses: </P>

Where can a synapse be located on a neuron
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