Demonstration

We have just seen how the electrical signal—the action potential—is passed from a presynaptic cell (a neuron) to a postsynaptic cell (a muscle cell) via the chemical synapse using the neurotransmitter acetylcholine.

In the human brain, more than 25 neurotransmitters are now recognized, and which neurotransmitter is used by a particular neuron will determine whether a synapse is excititory or inhibitory. In addition, each neurotransmitter may bind to several receptor subtypes. Ultimately, the action of a particular neurotransmitter will depend on the receptor to which it binds.

Note that in this animation we have depicted only a single synaptic vesicle within the terminal. An actual synapse contains a multitude of synaptic vesicles. In addition, the arrival of the action potential triggers the release of neurotransmitter only from those vesicles closest to the synaptic membrane. Vesicles farther away from the membrane then move into position in preparation for another round of transmitter release.