The first neurotransmitter ever identified: it moves every skeletal muscle, slows the heart, sharpens attention and memory — and is the target of curare, nerve agents, Alzheimer's drugs and myasthenia gravis.
Neurotransmitters & Brain Chemistry
Intermediate
Acetylcholine
The Editors
December 21, 2025
2 min read
In plain English
Acetylcholine is the chemical that nerves use to tell your muscles to contract. In the brain it helps with attention and memory. Some poisons and diseases block it, and some Alzheimer's medicines work by making it last longer.
Intermediate level: Builds on the basics. Introduces the real vocabulary and the mechanisms behind it.
Concepts to know first
Go deeper next
Acetylcholine (ACh) holds a special place in history: it was the first neurotransmitter identified, thanks to Otto Loewi's frog-heart experiment (1921) and the work of Henry Dale.
Moving muscles
Every voluntary movement you make depends on acetylcholine. Motor neurons release it at the neuromuscular junction, where it binds nicotinic receptors on muscle fibres, triggering contraction. The enzyme acetylcholinesterase breaks it down within milliseconds, so each signal is brief.
Interfering with this system is dangerous. Curare, a South American arrow poison, blocks nicotinic receptors and paralyses muscles; related drugs are used during surgery. Nerve agents such as sarin, and some insecticides, block acetylcholinesterase so ACh builds up, causing uncontrolled muscle activity and paralysis of breathing. In myasthenia gravis, the immune system attacks acetylcholine receptors, causing fatigable weakness — drooping eyelids and double vision are common early signs.
Running the body's automatic systems
ACh is also the main transmitter of the parasympathetic nervous system, acting through muscarinic receptors to slow the heart, stimulate digestion and constrict the pupils. Atropine, from deadly nightshade, blocks these receptors — Renaissance women reportedly used nightshade drops to widen their pupils, hence the plant's name belladonna, "beautiful lady".
Attention and memory
In the brain, cholinergic neurons in the basal forebrain (especially the nucleus basalis of Meynert) project across the cortex and hippocampus, boosting attention, learning and the brain's response to new information. These neurons are lost early in Alzheimer's disease, and drugs such as donepezil, which inhibit acetylcholinesterase, give modest symptomatic benefit. Nicotine acts on nicotinic receptors in the brain, which partly explains its effects on alertness — and its addictiveness.
Everyday examples & things to try
Analogy
A message that erases itself
At the neuromuscular junction, acetylcholine is like a message written in disappearing ink — the enzyme acetylcholinesterase wipes it within milliseconds. Nerve agents stop the eraser, so the message keeps shouting and the muscles can't stop responding.
Key takeaways
- Acetylcholine triggers skeletal muscle contraction via nicotinic receptors.
- It runs much of the parasympathetic system via muscarinic receptors.
- Basal forebrain ACh supports attention and memory and declines in Alzheimer's disease.
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