Nervous Control of Micturition

Micturition (urination) is:

Correct Answer: Parasympathetic activity

Micturition (urination) is primarily a parasympathetic activity. The sympathetic nervous system has no significant role in micturition itself.

Neural Control of Micturition

• Parasympathetic nerves (pelvic nerves, S2–S4): Contract the detrusor muscle (bladder wall) + Relax the internal urethral sphincter → Urine is expelled
• Sympathetic nerves (hypogastric nerve, L1–L2): Relax the detrusor muscle + Contract the internal sphincter → Storage phase; sympathetics PREVENT micturition during bladder filling
• Somatic nerve (pudendal nerve): Controls the external urethral sphincter (voluntary control)

Micturition Reflex

Bladder fills → stretch receptors activated → afferent signals to sacral spinal cord → parasympathetic efferent → detrusor contraction + sphincter relaxation → voiding. This reflex is modulated by higher brain centres (pontine micturition centre).

Key Terminology

• Micturition: Process of emptying the urinary bladder (also called urination)
• Polyuria: Increased urine output
• Oliguria: Decreased urine output
• Anuria: No urine output
• Stranguria: Slow, dropwise, painful discharge of urine due to spasm of urethra and bladder