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Frog neuromuscular junction fly-through. Shown in red is a large muscle fiber (diameter 50 micrometers) that is innervated by a myelinated axon colored in white. The interface between muscle and axon form the neuromuscular junction.
Upon approaching the neuromuscular junction its constituent 24 active zones become visible. Each active zone contains two rows of 13 synaptic vesicles (gold) that are docked at the pre-synaptic membrane and a similar number of calcium channels located in the valley between the two rows (open and closed channels are colored in blue and red, respectively). The calcium channels release calcium ions during nerve stimulation and eventually trigger the release of the neurotransmitter filled docked synaptic vesicles via sensor sites located at the bottom of each vesicle (black).
The active zone volume is filled with a reserve pool of synaptic vesicles (gold) and also ...
