What are, in order, the steps from a spike in the axon to transmitter in the cleft? · Lobeworks/17

The depolarisation wave runs down the axon and reaches the presynaptic terminal.

What are, in order, the steps from a spike in the axon to transmitter in the cleft?

The depolarisation wave runs down the axon and reaches the presynaptic terminal. There it opens voltage-gated calcium channels, and calcium flows in on the spike's falling flank. Calcium binds synaptotagmin on a synaptic vesicle that the SNARE complex holds primed at the active zone. Synaptotagmin triggers fusion, which is exocytosis, and the vesicle empties one quantum of transmitter into the synaptic cleft, which it crosses in microseconds to reach the receptors.