Acupuncture and Hormone Balance
Chapter 5: Acetylcholine
Acetylcholine was the first neurotransmitter, a chemical that nerve cells use to communicate, to be identified. It functions in both the peripheral (all the nerves except the brain and spinal cord) and the central (the brain and spinal cord) nervous systems. Acetylcholine serves as the only neurotransmitter in the parasympathetic nervous system. The function of acetycholine depends on its receptors (certain kinds of protein that a chemical messenger interacts with to modify cell activities). There are two types of acetylcholine receptors: nicotinic and muscarinic. Nicotinic receptors, which have many subtypes, are found at the junction between nerve and muscle where they control muscle movement and tone in the autonomic nervous system and in parts of the central nervous system. Muscarinic receptors in smooth muscles regulate cardiac contractions, gut motility, and bronchial constriction. Muscarinic receptors in exocrine glands stimulate gastric acid secretion, salivation, and lacrimation. In the brain, muscarinic receptors are found in the cerebral cortex, striatum, hippocampus, thalamus, and brainstem.
Functions of Acetylcholine
Generally, acetylcholine stimulates the contraction of smooth muscle such as intestinal and bronchial muscles.
Acetylcholine stimulates secretion from glands such as the tear glands, stomach glands, and salivary glands.
Acetylcholine dilates blood vessels and lowers blood pressure by using different mechanisms that affect the endothelial cells (the lining cells) inside blood vessels. If the endothelium is removed, acetylcholine exerts a stimulatory effect on vascular smooth muscle, just as it stimulates other smooth muscle cells.
Imbalance of Acetylcholine and Diseases
Acetylcholine has the opposite effect on small blood vessels than on bronchial or intestinal smooth muscles. When the level of acetylcholine increases or decreases, it may influence both functions. How each person responds to this chemical depends on his or her genetic make up which in turn, determines what kinds of receptor subtypes are located in different tissues. High acetylcholine levels in the body (induced by the inhibition of acetylcholinesterase, the enzyme that breaks down acetylcholine) are associated with gastrointestinal cramping, asthma, increased salivation, lacrimation, and urination, nasal congestion, and phlegm in the throat...