Which physiologic process will relax the detrusor muscle?

The relaxation of the detrusor muscle, which is the smooth muscle of the bladder, is primarily influenced by the activation of beta-2 (β-2) adrenergic receptors. When the sympathetic nervous system is activated, it releases norepinephrine that binds to the β-2 receptors on the detrusor muscle. This binding leads to muscle relaxation, facilitating bladder filling and the storage of urine.

This physiological response is particularly important in maintaining urinary continence. The activation of these receptors promotes a decrease in the contractile activity of the detrusor muscle, contrasting with the action of the parasympathetic nervous system, which typically promotes contraction of the detrusor muscle through muscarinic (M3) receptor activation. Thus, while muscarinic receptors are involved in stimulating the bladder to contract and facilitate urination, β-2 receptor activation is responsible for promoting relaxation of the detrusor muscle, enabling the bladder to fill without involuntary contractions.