part of part of terminal bouton terminal button cellular_component Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal bouton is a specialized region of it. presynaptic bouton bouton NIF_Subcellular:sao187426937 synaptic bouton GO:0043195 axon terminus presynapse