Illustration of the major elements in chemical synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron. When the action potential reaches the presynaptic terminal, it provokes the release of a small quantity of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of another neuron, the postsynaptic neuron, on the opposite side of the synaptic cleft.
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of the synapse.
Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may also follow graded electrical potentials.
Low level “baseline” release also occurs without electrical stimulation.
Neurotransmitters are synthesized from plentiful and simple precursors, such as amino acids, which are readily available from the diet and which require only a small number of biosynthetic steps to convert.
Ramón y Cajal (1852–1934): Discovered a ‘ 20 to 40’ nm gap between neurons, known today
as the synaptic cleft.