The place of near contact between two neurons is called the synapse. When the neural impulse (action potential) reaches the axon terminals of the presynaptic neuron, the synaptic vesicles containing neurotransmitter molecules fuse with the presynaptic membrane. The neurotransmitter molecules are then released into the synaptic cleft (the gap between the two neurons). The neurotransmitter molecules then bounce on and off of receptor sites located in the postsynaptic membrane. In order to bind to the postsynaptic receptor, the neurotransmitter molecule must fit into the receptor like a key fits into a lock. When the neurotransmitter molecule binds to the receptor an EPSP or IPSP is produced in the postsynaptic neuron. Before synaptic transmission can reoccur, the neurotransmitter must be inactivated, either through reuptake (into the presynaptic terminal) or by metabolic destruction via enzyme in the synaptic cleft.
In the animation below, the "Pac-man"-like symbols represent the destructive enzyme. Click on the "Play" button to see the process of synaptic transmission demonstrated. Be sure to click on the "Rewind" button before replaying the animation. To stop the animation at any point in time, click on the unlabeled button between the "Play" and "Rewind" buttons.