Which urethral sphincter is voluntary?

Which urethral sphincter is voluntary?

• A. External
• B. Internal
• C. Both
• D. None

Answer: (A)

The ability to hold urine and control its release comes from two different urethral sphincters. The one you can consciously tighten is the external urethral sphincter, a skeletal (striated) muscle in the pelvic floor. It is under somatic control through the pudendal nerve (S2–S4), which lets you voluntarily contract to keep urine in. In contrast, the internal urethral sphincter is smooth muscle located at the bladder neck and urethra, controlled by the autonomic nervous system. It stays closed largely on its own and relaxes reflexively to allow voiding when appropriate, not through conscious control. So, the voluntary sphincter is the external urethral sphincter. Strengthening it with pelvic floor exercises can improve continence. During urination, you relax this external sphincter and permit the detrusor to contract.

The ability to hold urine and control its release comes from two different urethral sphincters. The one you can consciously tighten is the external urethral sphincter, a skeletal (striated) muscle in the pelvic floor. It is under somatic control through the pudendal nerve (S2–S4), which lets you voluntarily contract to keep urine in.

In contrast, the internal urethral sphincter is smooth muscle located at the bladder neck and urethra, controlled by the autonomic nervous system. It stays closed largely on its own and relaxes reflexively to allow voiding when appropriate, not through conscious control.

So, the voluntary sphincter is the external urethral sphincter. Strengthening it with pelvic floor exercises can improve continence. During urination, you relax this external sphincter and permit the detrusor to contract.