Acetylcholine

Acetylcholine is an important neurotransmitter that is involved in a variety of human physiological processes such as muscle contractions, learning and memory, and motor control. Acetylcholine is produced in the central and peripheral nervous systems and serves as the main neurotransmitter in the parasympathetic nervous system, which controls the body's involuntary functions such as digestion and respiration. It is also involved in alertness, wakefulness, and arousal. In terms of structure, acetylcholine is composed of two parts, a nitrogen-containing base and an acetic acid head. The base is an acetyl group, which is composed of a pair of carbon atoms and two oxygen atoms, and the head is a quaternary amino group, composed of a nitrogen atom and three hydrogen atoms. The two parts are joined together by an ester linkage. Acetylcholine is synthesized in neurons from the precursor molecules, acetyl coenzyme A (acetyl-CoA) and choline, through the enzyme choline acetyltransferase (ChAT). Acetylcholine is released into the synaptic cleft from vesicles by exocytosis and reacts with receptor proteins which are located on the post-synaptic neuron. The activity of these receptors can be either excited or inhibited, depending on the concentration of acetylcholine in the synaptic cleft which could be regulated by the amount of choline acetyltransferase (ChAT) in neurons.