Axon terminal

Axon terminals (also called synaptic boutons, presynaptic terminals, or end-feet) are distal terminations of the branches of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body in order to transmit those impulses to other neurons, muscle cells or glands. In the central nervous system, most presynaptic terminals are actually formed along the axons (en-passant boutons), not at their ends (terminal boutons).

Functionally, the axon terminal converts an electrical signal into a chemical signal. When an action potential arrives at an axon terminal (A), neurotransmitter is released and diffuses across the synaptic cleft. If the postsynaptic cell (B) is also a neuron, neurotransmitter receptors generate a small electrical current that changes the postsynaptic potential. If the postsynaptic cell (B) is a muscle cell (neuromuscular junction), it contracts.