The primary chemical messenger responsible for the “rest and digest” response within the body is acetylcholine. This molecule acts at the junctions between parasympathetic nerve fibers and the organs they innervate, including glands, smooth muscle, and cardiac muscle. For example, acetylcholine released onto cardiac muscle slows heart rate, while its action on smooth muscle in the digestive tract promotes increased motility and secretion.
Regulation of these essential bodily functions by this neurotransmitter is critical for maintaining homeostasis and conserving energy. The opposing actions of the sympathetic (“fight or flight”) and parasympathetic nervous systems ensure a balanced physiological response to internal and external stimuli. Understanding the role of acetylcholine in the parasympathetic system has been instrumental in developing treatments for various medical conditions, including heart disease and gastrointestinal disorders.
