Neurotransmitters are special chemicals which help to pass nerve impulses on from one neuron to another. When a nerve impulse runs down the axon of a neuron, ultimately it arrives at the axon terminal, where the synaptic knobs are located. The synaptic knobs contain packets (vesicles) of specialized chemicals, the neurotransmitters. When the nerve impulse reaches the synaptic knobs, the vesicles spill out into a space located between the axon terminal and the next neuron's cell body or soma. This space is referred to as the synapse, or synaptic junction.

The neurotransmitters spread across the synaptic junction, until they reach the next neuron's soma, where they attach themselves to special receptors along the soma's membrane. This allows the nerve impulse to continue to be transmitted along this next neuron's axon.

Almost immediately, special enzymes also arrive in the synaptic junction, to degrade any leftover neurotransmitters lingering there. This...