Fig. 15. The SynapticVesicle.

1. The synaptic vesicle accumulates hydrogen ions at the expense of ATP. The hydrogen ions are then exchanged for acetylcholine (red), a neurotransmitter, by a specific antiport protein.

2. As the vesicle becomes charged with acetylcholine, it is picked up by a cytoplasmic transport protein and carried through the cytoplasm to the synaptic region of the neuron.

3. The filled vesicle is docked in the region of the synapse, where it awaits a nerve stimulation.

4. Triggered by an influx of calcium ions, the vesicle releases its charge of acetylcholine to the synapse, passing the impulse on to the post-synaptic cell.

5. The empty vesicular membrane is surrounded by cytoplasmic protein molecules called clathrin (blue), capturing the vesicle for reuse. The clathrin forms a cage coating the entire vesicle. The vesicle then travels back away from the membrane into the cytoplasm and loses its protective cage.

6. The vesicle again begins to accumulate hydrogen ions the cycle is repeated.

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