A synapse is the junction between two neurons, or between a neuron and a target cell such as a muscle or gland, where information is transmitted. It consists of the presynaptic terminal, the synaptic cleft (a gap of about 20–40 nanometres), and the postsynaptic membrane.

Most synapses in the nervous system are chemical: an electrical signal arriving at the axon terminal triggers the release of neurotransmitters into the cleft, which bind to receptors on the next cell and either excite or inhibit it. Some synapses are electrical, allowing ions to flow directly between cells through gap junctions, which makes transmission faster but less flexible.

Key features

• Presynaptic terminal releases neurotransmitters
• Synaptic cleft separates the two cells
• Postsynaptic receptors receive the signal
• Transmission is unidirectional in chemical synapses

Synaptic plasticity—the strengthening or weakening of synapses with use—is widely considered the cellular basis of learning and memory.