The detrusor muscle receives parasympathetic innervation from which nerves?

• A. Pelvic splanchnic nerves (S2-4)
• B. Hypogastric nerves
• C. Pudendal
• D. Lumbar splanchnic

Answer: (A)

Parasympathetic activation of the detrusor comes from the sacral spinal cord via the pelvic splanchnic nerves (S2–S4). These fibers travel to the inferior hypogastric plexus and then to the bladder wall, where they release acetylcholine onto muscarinic receptors (primarily M3) to induce detrusor contraction and promote voiding. The hypogastric nerves carry sympathetic input that supports storage by relaxing the detrusor and contracting the internal sphincter, the pudendal nerve provides somatic control of the external urethral sphincter, and lumbar splanchnic nerves carry other sympathetic fibers not responsible for detrusor parasympathetic innervation.