Chemical released by neuron s to stimulate neighbouring neurons, allowing impulses to be passed from one cell to the next throughout the nervous system .
A nerve impulse arriving at the axon terminal of one neuron stimulates release of a neurotransmitter, which crosses the microscopic gap (see synapse ) in milliseconds to the adjoining neuron's dendrite. Many chemicals are believed to act as neurotransmitters. The few that have been identified include acetylcholine , dopamine , and serotonin . Some neurotransmitters activate neurons; others inhibit them. Some mind-altering drugs act by changing synaptic activity.