The minute gap between presynaptic cell and postsynaptic cell in a chemical synapse, across which the neurotransmitters diffuse into.
This gap acts as a site where neurotransmitters from presynaptic cell (e.g. neuron) are released into by exocytosis and diffuses across to bind with the receptors in the cell membrane of postsynaptic cell. This gap is only a minute space allowing the concentration of neurotransmitters to be raised and lowered rapidly.
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 cell (neural or otherwise). 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 Greek synapsis "conjunction," from synaptein "to clasp," from syn- "together" and haptein "to fasten") was introduced in 1897 by English physiologist Michael Foster at the suggestion of English classical scholar Arthur Woollgar Verrall.
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 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, but some presynaptic sites are located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission.
Two most important ways by which neurotransmitters are removed from synaptic cleft: