A physical therapist lists three motor signals that must be coordinated for normal voiding. Which list correctly includes all three?

A physical therapist lists three motor signals that must be coordinated for normal voiding. Which list correctly includes all three?

• A. Contraction of the detrusor muscle, relaxation of the internal urinary sphincter, and relaxation of the external urinary sphincter
• B. Relaxation of the detrusor muscle, contraction of the internal urinary sphincter, and contraction of the external urinary sphincter
• C. Contraction of the detrusor muscle, contraction of the internal urinary sphincter, and relaxation of the external urinary sphincter
• D. Relaxation of the detrusor muscle, relaxation of the internal urinary sphincter, and relaxation of the external urinary sphincter

Answer: (A)

Normal voiding requires the bladder to actively contract while the outlet becomes open. The detrusor muscle contracts to push urine out, raising bladder pressure. At the same time, the internal urethral sphincter (smooth muscle) must relax to allow urine to pass through the internal outlet, and the external urethral sphincter (skeletal muscle) must relax as well to permit flow through the external opening. This coordinated trio—detrusor contraction with relaxation of both sphincters—is what enables normal micturition. If any sphincter remained tight or the detrusor failed to contract, voiding would be hindered. That’s why the correct combination is detrusor contraction with relaxation of the internal and external sphincters.

Normal voiding requires the bladder to actively contract while the outlet becomes open. The detrusor muscle contracts to push urine out, raising bladder pressure. At the same time, the internal urethral sphincter (smooth muscle) must relax to allow urine to pass through the internal outlet, and the external urethral sphincter (skeletal muscle) must relax as well to permit flow through the external opening. This coordinated trio—detrusor contraction with relaxation of both sphincters—is what enables normal micturition. If any sphincter remained tight or the detrusor failed to contract, voiding would be hindered. That’s why the correct combination is detrusor contraction with relaxation of the internal and external sphincters.