Muscarinic receptors in the bladder primarily mediate which action?

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Multiple Choice

Muscarinic receptors in the bladder primarily mediate which action?

Muscarinic receptors on the detrusor muscle are the main drivers of bladder contraction when acetylcholine is released by parasympathetic nerves. The M3 subtype, in particular, couples to Gq to raise intracellular calcium, triggering smooth muscle contraction and powerful detrusor squeeze to expel urine. While M2 receptors exist, they play a secondary, modulatory role rather than directly causing contraction. This is why detrusor contraction is the best answer. Bladder relaxation, by contrast, is primarily mediated by beta-adrenergic receptors (especially beta-3) that relax the detrusor. The internal urethral sphincter is controlled mainly by sympathetic activity (causing contraction), not muscarinic signaling. Sensory signal amplification is not the principal action of these receptors in the bladder.

Muscarinic receptors on the detrusor muscle are the main drivers of bladder contraction when acetylcholine is released by parasympathetic nerves. The M3 subtype, in particular, couples to Gq to raise intracellular calcium, triggering smooth muscle contraction and powerful detrusor squeeze to expel urine. While M2 receptors exist, they play a secondary, modulatory role rather than directly causing contraction.

This is why detrusor contraction is the best answer. Bladder relaxation, by contrast, is primarily mediated by beta-adrenergic receptors (especially beta-3) that relax the detrusor. The internal urethral sphincter is controlled mainly by sympathetic activity (causing contraction), not muscarinic signaling. Sensory signal amplification is not the principal action of these receptors in the bladder.

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