How does a spike arriving at a terminal turn into released transmitter? · Grey Matter

The spike depolarises the terminal and opens voltage-gated calcium channels clustered at the release sites.

How does a spike arriving at a terminal turn into released transmitter?

The spike depolarises the terminal and opens voltage-gated calcium channels clustered at the release sites. Calcium enters and binds synaptotagmin on vesicles that the SNARE proteins (synaptobrevin on the vesicle, syntaxin and SNAP-25 on the terminal) have already half-zipped to the membrane. The calcium-bound synaptotagmin lets the zipping finish, the two membranes fuse and the vesicle empties into the cleft, all in well under a millisecond. Blocking the calcium channels blocks release, which is how calcium was shown to be the link.