Which neurotransmitter system primarily drives detrusor contraction?

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Detrusor contraction is driven by the parasympathetic cholinergic system. Acetylcholine released from pelvic (parasympathetic) nerves binds to muscarinic receptors on the detrusor smooth muscle, mainly the M3 subtype, triggering a calcium-dependent contraction that propels urine out of the bladder. In contrast, the sympathetic system supports storage by relaxing the detrusor via beta-3 receptors and constricting the internal sphincter via alpha-1 receptors, so it’s not the driver of contraction. Dopaminergic and serotonergic systems modulate micturition at higher brain and spinal levels rather than directly causing detrusor contraction. Clinically, reducing cholinergic signaling with antimuscarinic drugs decreases detrusor contractions, illustrating the cholinergic mechanism behind bladder emptying.