Nitric Oxide (NO)

Nitric oxide functions as a signaling molecule that tells the body to make blood vessels relax and widen. This physiological reaction is important when the body needs more blood--the brain signals to the blood vessels near the arms, for example, when the arms need more blood supply for muscle movement or for warmth. Thus, NO works as a signaling molecule in the cardiovascular system, the nervous system, and in other tissues.

Signaling molecules in the nervous system are called neurotransmitters, and NO, as a gas, does not fit into the traditional form of neurotransmitters. Thus, scientists were surprised to find that NO functions as a neurotransmitter in the nervous system.