Why don't beta blockers interfere with skeletal muscles?

Question

1. Beta blockers are a group of drugs given after an acute myocardial infarction (heart attack) to reduce the sympathetic stimulation of the heart muscle. They work by blocking β1 adrenergic receptors on the heart muscle. So, why do these drugs not interfere with skeletal muscles like your biceps or triceps? You must provide a physiological explanation for your answer. You cannot say “because they are different muscle types”.

Answer 1

Remember, skeletal muscle is voluntary, i.e., controlled consciously, while cardiac muscle and smooth muscle) are involuntary forms of muscle that can function without our conscious control.

Also remember that for a cell to respond to an outside signal, e.g., neurotransmitter, hormone, it must have a receptor for that substance so the cell can bind the chemical and then react to it.

Skeletal muscle uses 'cholinergic' receptors that respond only to acetylcholine (ACh). Cholinergic receptors cannot bind epinephrine or norepinephrine.

Cardiac and smooth muscles use a different class of receptors called alpha (∝) and beta (ß) adrenergic receptors, which bind epinephrine and norepinephrine.

So, ß blockers can block the action of norepinephrine and epinephrine on cardiac muscle, but not on skeletal muscle since skeletal muscle does not have adrenergic receptors. Thus, skeletal muscle is unaffected by ß blockers.