Acetylcholine

If acetylcholine is removed from the circulation faster than norepinephrine is, which of the following autonomic processes would be most rapidly inactivated?
A. Dilation of the pupils
B. Dilation of blood vessels in the skeletal muscles
C. Rise in blood pressure
D. Stimulation of digestive secretions


Answer explanation says “Choices A, B, and C all describe sympathetic effects”. How is dilation of blood vessels in the skeletal muscles a sympathetic effect?

Acetylcholine is the chief neurotransmitter of the parasympathetic nervous system, the part of the autonomic nervous system (a branch of the peripheral nervous system) that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows heart rate.


@Emily_B

Yes, so if acetylcholine is responsible for dilating blood vessels, then B would be correct, but apparently it's not.

Blood vessels do not contain receptors for acetylcholine! The level of sympathetic stimulation determines blood vessels diameter i.e. more adrenaline/noradrenaline = vasoconstriction, less adrenaline/noradrenaline = vasodilation.

However, that’s not the main point of the question. While adrenaline/noradrenaline cause vasoconstriction in most vessels throughout the body, they actually cause vasodilation in skeletal muscles (they have different receptors) to increase blood flow in muscles. If you think about the fight or flight response, this makes sense, it increases blood flow to muscles to allow us to run or fight.

Don't blood vessels have smooth muscle, which is controlled by acetylcholine? As this source (https://pubmed.ncbi.nlm.nih.gov/11475798/) mentions: "Acetylcholine (ACh) may induce the relaxation and the contraction of human blood vessels. These effects involve the activation of muscarinic receptors located on endothelial or smooth muscle cells." But maybe as you said, most blood vessels don't have acetylcholine receptors.

As an aside, does sympathetic innervation cause mainly pressure increase or vascular resistance (i.e vessel diameter reduction)? Which is it more likely to affect?