Acetylcholine

Here are my notes on acetylcholine. Just so you can get an idea of what it does in the brain and in the body, and why it is important for cognition.

So acetylcholine (ACh) is one of many kinds of neurotransmitter that are found in the body. To be brief, neurotransmitters are the chemicals released by neurons to signal or “talk” to other neurons.

The name acetylcholine refers to its chemical structure: acetylcholine is a ester of acetic acid and choline.

The parts of the body that use or are affected by acetylcholine are referred to as cholinergic. Whereas substances that block acetylcholine from reaching its receptors, therefore stopping the action of acetylcholine, are known as anticholinergics.

What is Acetylcholine Used for in the Body?

If you recall, the parts of the body (“systems”) that use the acetylcholine neurotransmitter are called “Cholinergic Systems”. The cholinergic systems in the body play important roles in the function of memory, digestion, regulation of heart beat, blood pressure, movement, and more.

The Function of the Autonomic Nervous System Require Acetylcholine

One of the cholinergic systems in the body is called the Autonomic Nervous System (ANS). That means the ANS uses acetylcholine to function. The ANS is a system that functions below our level of consciousness, in other words it is more “automatic”. The Autonomic Nervous System controls our heart rate, digestion, respiration rate, salivation, perspiration, dilation of pupils, urination, and sexual arousal.

The Autonomic Nervous System is divided into 3 parts: the Sympathetic Nervous System (SNS), the Parasympathetic Nervous System (PSNS), and the Enteric Nervous System (ENS).

The SNS is primarily responsible for turning on the body’s fight-or-flight response, although it is constantly on for the body to maintain homeostasis.

The PSNS is said to be responsible for turning on the body’s rest-and-digest or feed and breed activities when the body is at rest. That means the parasympathetic nervous system controls our hunger, sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation.

The ENS is controls the function of the Gastrointestinal (GI) tract, for example controlling how quickly food passes through the GI tract.

Finally, you should note that acetylcholine is the messenger molecule required for the activation of receptors that cause the effects associated with all of these systems (SNS, PSNS, ENS).

Acetylcholine is a Muscle Messenger

Well, acetylcholine is one of the neurotransmitters that is used by the neurons that control the muscles. The neurons which control the muscles are called, “motor neurons”. When when these motor neurons release acetylcholine, the muscles activate and start contracting. This allows us to exercise, run, sprint, reach for a cup placed on a table. So in this way acetylcholine is a good thing.

But when there is too much acetylcholine released by the motor neurons, your muscles end up contracting too much and causing convulsions. And when there is too little acetylcholine available to the motor neurons, your muscles don’t contract enough and causes paralysis. This normally does not happen, except from exposure to certain poisons such as scolopamine, atropine, and sarin gas.

Acetylcholine is a Brain Messenger

In the brain, acetylcholine again functions both as a neurotransmitter and as a neuromodulator. Different parts of the brain is cholinergic, and have different function. The parts of the brain that use acetylcholine influence our arousal, alertness & attention, memory & learning, and motivation.

Specifically, the parts of the brain the uses acetylcholine and have ACh receptors run from the basal forebrain all the way to the cerebral cortex and the hippocampus. Without sufficient acetylcholine, these areas of the brain don’t function as efficiently. Therefore insufficient acetylcholine levels in the brain negatively impact our cognitive or brain function.

So having an optimal level of acetylcholine in the brain is desirable for optimal cognitive function, and therefore interest nootropic enthusiasts like me. After all, its not too hard to manipulate the level of Acetylcholine (ACh) in the brain- for example, you can use cardamom or especially rosemary essential oil to increase the level of ACh in the brain.

Acetylcholine (ACh) also has substantial role in our sleep-wake cycle. Neurons that contain ACh continually discharge it while we are awake. Whereas ACh neuronal release decreases slow-wave sleep. And finally ACh is released again at a high rate during paradoxical sleep, a.k.a. Rapid-Eye-Movement (REM) sleep.^[1] The high ACh levels may be required for REM sleep to occur, and thereby ACh may be responsible for the vivid dreams that we see.

And it makes sense too. Dreaming is like hallucinating. In fact, I bet that hallucinogens like psilocybin make use of acetylcholine receptors in the brain in order to make the person see hallucinations. Or contribute to it. But I still need to confirm this with scientific studies.

Random Notes

I haven’t yet decided where to fit some of the information of acetylcholine in my article. So instead of forgetting about them, I’ll list them right here:

• Scolopamine blocks the effect of acetylcholine (therefore is a anticholinergic), including in the brain. This explains why some people experience memory loss after they are exposed to scolopamine.
• Atropine is another type of anticholinergic that specifically inhibits or turns down the parasympathetic nervous system.
• Two of the main types of Acetylcholine Receptors (AChR) found in the human body are called “Muscarinic” and “Nicotinic” receptors. These receptors are named according to their affinity for muscarine and nicotine drugs, respectively.

Related Links

Sources

1. From waking to sleeping: neuronal and chemical substrates. [Trends Pharmacol Sci.]
2. Basic and modern concepts on cholinergic receptor: A review [Asian Pac J Trop Dis.]