Neurotransmitters are chemicals released in minute amounts from the terminals of nerve cells in response to the arrival of an action potential. There are now more than 300 known neurotransmitters and they act either locally in point-to-point signal transmission (e.g., the motor nerve of a neuromuscular junction) or at a distal site (e.g., the hypothalamic releasing hormones acting on the anterior pituitary). Locally acting neurotransmitters relay the electrical signal travelling along a neuron as chemical information across the neuronal junction, or synapse, that separates one neuron from another neuron or a muscle. Neurons communicate with peripheral tissues, such as muscles, glands etc., or with each other largely by this chemical means rather than by direct electrical transmission.

Neurotransmitters are stored in the bulbous end of the nerve cell's axon. When an electrical impulse travelling along an axon reaches the junction, the neurotransmitter is released and diffuses across...