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Discovery, construction and function
The neurotransmitter acetylcholine (ACh) is considered the most important neurotransmitter due to its elementary control function of vegetative processes in vertebrates. In 1921, acetylcholine, the first neurotransmitter ever, was discovered by pharmacologist Otto Loewi in experiments with frog hearts. Loewi realized that the control of heart rate could not be based solely on electrical conduction, since the fluid from the heart environment of any frog, even with other frogs to stimulate the heartbeat led. The heart rate had to be controlled by a, located in the liquid heart, chemical component (formerly known as vagus substance, today: acetylcholine).
Acetylcholine (C7H16NO2) is produced in the organism from acetyl-coenzyme A (CH3CO-) and choline (C5H14ClNO). The enzyme choline acetyltransferase serves as a catalyst. The acetylcholine is degraded by the enzyme acetylcholinesterase, which splits the acetylcholine back into choline and acetic acid.
Acetycholine is the mediating transmitter between nerve endings and muscle fiber. At the motor end plate, incoming action potentials provide for the release of acetylcholine in the synaptic cleft. ACh binds to the acetylcholine receptors of the postsynaptic membrane and causes the influx of sodium and calcium ions by opening voltage-dependent ion channels. In this way, it leads to a transmission of the excitement on the muscle cell, and in the further course to muscle contraction. According to this principle, all the muscles in the human body function.
In addition, acetylcholine is also involved in the control of the autonomic nervous system: blood pressure, heartbeat, respiration, digestion, metabolism and even brain activity are controlled by the transmitter. In this regard, acetylcholine is particularly useful in degenerative brain diseases, e.g. Alzheimer's, a not inconsiderable, if not central, role too.