The detrusor muscle is innervated by which nerves?

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

Answer: (C)

Parasympathetic innervation drives bladder emptying. The detrusor muscle, the smooth-walled wall of the bladder, receives its parasympathetic supply from the pelvic splanchnic nerves carrying fibers from S2–S4. These fibers reach the bladder via the pelvic plexus and release acetylcholine onto muscarinic receptors (primarily M3) on the detrusor, causing it to contract and propel urine out through the urethra.

In contrast, the hypogastric nerves provide sympathetic input that promotes storage by relaxing the detrusor and contracting the internal sphincter, while the pudendal nerve supplies the external (skeletal) urethral sphincter for voluntary control. The femoral nerves are not involved in bladder innervation.