Axon Terminal Buttons:

Axon terminal buttons, also called terminal buttons, synaptic end bulbs,or synaptic end boutons, are a small, bulbous structure at the axon terminal — a part of the presynaptic terminal (the axon’s entire region is involved in synaptic transmission). When the electrical signal reaches the terminal button, it triggers tiny sacs within synaptic vesicles to release neurotransmitters (chemical messengers) into the synaptic cleft, to transmit signals to the next “receiving” neuron’s postsynaptic terminals. After neurotransmitters are released, some are reabsorbed by the presynaptic terminal button through a process called reuptake. Also see Serotonin and Norepinephrine Reuptake Inhibitors (SNRIs)