ACETYLCHOLINE

The messenger at the muscle

At the neuromuscular junction a motor neuron releases acetylcholine onto nicotinic receptors, and the muscle contracts.

Every voluntary movement depends on this one handoff.

FAST CLEANUP

Broken down in a flash

Enzyme Acetylcholinesterase (AChE) breaks acetylcholine down within about a millisecond

Nerve agents Block AChE, so acetylcholine floods the synapse and muscles seize

Myasthenia gravis The immune system attacks the muscle's receptors, causing weakness

When cleanup fails, the message never stops.

IN THE BRAIN

Attention and memory

Acetylcholine in the brain supports attention, learning, and memory. In Alzheimer's disease, cholinergic neurons are lost. Drugs such as donepezil inhibit acetylcholinesterase, which lets the remaining acetylcholine act for longer and eases some symptoms.

Blocking an enzyme can make a weak signal stronger.

NOREPINEPHRINE

The alertness molecule

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Made from dopamine

One more chemical step turns dopamine into norepinephrine

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Alert and ready

Raises arousal and attention, and is part of the fight-or-flight response

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Drug target

Some ADHD and antidepressant drugs raise norepinephrine

It's the chemical cousin of adrenaline.

THE SLOWER ONES

Neuropeptides and gases

Neuropeptides such as the endorphins are chains of amino acids, much larger than the classic transmitters. They are released during strong activity, diffuse farther, and act more slowly and for longer. Small gases such as nitric oxide also act as messengers.

Not all messages are fast and local.

UNIT 9 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered acetylcholine, norepinephrine, and the larger, slower neuropeptides.