.jpg)
Neurones do not physically touch one another; two neurones are separated by a gap, known as a synaptic cleft.[1] Because neurones do not touch, and an action potential cannot ‘jump’ across a synaptic cleft, the signal must be converted to a chemical signal to enable communication between neurones to occur.[1] The presynaptic neurone uses chemical signals (neurotransmitters) to increase (excite) or decrease (inhibit) the generation of action potentials in the postsynaptic neurone. It is also possible to effect other biochemical processes, such as cell signalling pathways, in the postsynaptic neurone. This complex interconnectivity gives rise to the rich functional communication network that is the central nervous system.[1]
Presynaptic neurone – a neurone from which an electrical impulse is transmitted across a synaptic cleft to a postsynaptic neurone by the release of a chemical neurotransmitter. Postsynaptic neurone – a neurone to which an electrical impulse is transmitted across a synaptic cleft by the release of a chemical neurotransmitter from the axon terminal of a presynaptic neurone.
Reference:
[1] Kandel ER, Schwartz JH, Jessell TM (eds). Principles of Neural Science. 4th edition. McGraw-Hill, 2000.