Synapse (axon terminals and boutons)

Synapsis; boutons terminaux

NervousNervesWhole body

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What it is
The axon ends in fine terminal branches whose swollen tips (boutons) come within 20-40 nanometres of the next cell. Each bouton is packed with vesicles of neurotransmitter lined up at the release zone facing the synaptic cleft.
Function
Converts the electrical impulse into a chemical message: calcium entering the bouton triggers vesicles to release transmitter (e.g. acetylcholine or glutamate) that binds receptors on the next cell.
Size
Boutons 1-2 micrometres; synaptic cleft 20-40 nanometres
Clinical note
Most nerve drugs and toxins act here - antidepressants, botulinum toxin (blocks acetylcholine release) and nerve agents; in myasthenia gravis antibodies attack the acetylcholine receptors.

Part of Neuron cell body (soma) - magnified

Nearby nervous structures Accessory nerve (CN XI), Axon, Brachial plexus, Cervical plexus, Dendrites, Left phrenic nerve, Myelin sheath, Neuron nucleus, Nodes of Ranvier, Postsynaptic dendrite of the next neuron