Small Switches
Asystole

The room goes quiet, the heart keeps time,
Small switches work beneath the light.

Preganglionic fibres, both divisions,
Acetylcholine starts the relay.
Nicotinic gates in the ganglion
Let the next cell carry on its way.
Most sympathetic endings send
Norepinephrine to the organ wall.
Parasympathetic endings use
Acetylcholine for the final call.

Alpha one tightens vessel walls,
Alpha two can quiet release.
Beta one, heart faster, stronger,
Beta two lets airways ease.
Beta three relaxes detrusor,
M two slows the heart's own beat.
M three brings gland secretions,
Helps the gut and bladder squeeze.

Alpha two, presynaptic feedback,
Less norepinephrine sent.
Beta one in kidney cells
Can raise the renin they release.
Beta two in muscle vessels
Can let their smooth walls relax.
M three makes the pupil smaller,
Contracts the bladder, moves the tract.
Sweat glands keep a special connection:
Sympathetic fibres, acetylcholine.
Muscarinic receptors answer;
Keep that exception in the scene.

Alpha one tightens vessel walls,
Alpha two can quiet release.
Beta one, heart faster, stronger,
Beta two lets airways ease.
Beta three relaxes detrusor,
M two slows the heart's own beat.
M three brings gland secretions,
Helps the gut and bladder squeeze.

Alpha one and M three, G Q;
Alpha two and M two, G I.
Beta one, two, three, G S,
A first map of the signals inside.
Endothelium, M three:
Nitric oxide lets vessels ease.
Read the receptor and where it lies,
Same signal, different replies.

Alpha one tightens vessel walls,
Alpha two can quiet release.
Beta one, heart faster, stronger,
Beta two lets airways ease.
Beta three relaxes detrusor,
M two slows the heart's own beat.
M three brings gland secretions,
Helps the gut and bladder squeeze.

Read the receptor and where it lies,
Small switches under ordinary skies.