Which muscle aids in the voluntary control of urine flow?

The external urethral sphincter plays a crucial role in the voluntary control of urine flow. This skeletal muscle surrounds the urethra and is under conscious control, allowing an individual to decide when to start and stop the flow of urine. When the external urethral sphincter contracts, it keeps the urethra closed, thereby preventing urination. Conversely, when it relaxes, urine can flow out of the bladder. This voluntary control is essential for continence in both men and women.

In contrast, the detrusor muscle is responsible for bladder contraction and is involuntarily controlled, meaning it does not confer voluntary control over urination. The internal urethral sphincter, also involuntary, helps maintain closure to prevent urine leakage but does not allow for conscious regulation. Cardiac muscle relates to the heart and has no direct role in urine flow. Thus, the external urethral sphincter is the correct choice as it specifically enables voluntary control over urination.