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To read the previous article in this series, click here.
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Using the vitamins thiamin (B1), riboflavin (B2), niacin (B3), and pantothenic acid (B5), the brain makes acetyl-CoA out of glucose (or ketones, for the fat-adapted) in the brain. The acetyl group of acetyl-CoA is then combined with choline, which was taken up into the cell using sodium and originally derived either de novo in the liver or through dietary intake. The result is acetylcholine, one of the most important neurotransmitters in the brain, along with the more familiar glutamate, glycine, gamma-aminobutyric acid (GABA), dopamine, norepinephrine, and serotonin.
THE BREAKDOWN OF CHOLINE
When acetylcholine enters the synaptic cleft, it is cleared by an enzyme called acetylcholinesterase, which is in the synaptic cleft. Acetylcholinesterase cleaves the acetate from the acetylcholine molecule, breaking the molecule down into acetate and choline. The choline is then resynthesized and recycled into acetylcholine. The neurotransmitter acetylcholine and the enzyme acetylcholinesterase will be the subjects of much of this blog post.
CHOLINE & THE PARASYMPATHETIC SYSTEM
If you watch my YouTube videos, you’ll known that our bodies have two autonomic nervous systems: the sympathetic (‘fight-or-flight’) and the parasympathetic (‘rest and digest,’ or ‘feed and breed’). Acetylcholine is the primary neurotransmitter of the parasympathetic nervous system. The cholinergic system regulates sensory processing, sleep, arousal, and most importantly, for our purposes, attention. In the peripheral nervous system, acetylcholine is excitatory, while in the central nervous system, it is neuromodulatory.
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 Li, X., Yu, B., Sun, Q., Zhang, Y., Ren, M., Zhang, X., ... & Zeng, H. (2018). Generation of a whole-brain atlas for the cholinergic system and mesoscopic projectome analysis of basal forebrain cholinergic neurons. Proceedings of the National Academy of Sciences, 115(2), 415-420.  Gandelman, J. A., Newhouse, P., & Taylor, W. D. (2018). Nicotine and networks: potential for enhancement of mood and cognition in late-life depression. Neuroscience & Biobehavioral Reviews, 84, 289-298.