Anatomy and Physiology II Practice Test

The involuntary muscle at the exit of the bladder is known as?

1. External urethral sphincter

2. Internal urethral sphincter

3. Detrusor muscle

4. Pelvic floor muscle

The correct answer is: Internal urethral sphincter

The internal urethral sphincter is the structure that controls the release of urine from the bladder. This sphincter is composed of smooth muscle, which is why it is considered involuntary. It surrounds the opening of the urethra from the bladder, and its contraction helps to maintain continence by preventing urine from leaking out. When the bladder fills, signals are sent to the brain that facilitate the relaxation of the internal urethral sphincter, allowing urine to flow through the urethra during micturition. In contrast, the external urethral sphincter is composed of skeletal muscle, making it under voluntary control, which is different from the involuntary nature of the internal sphincter. The detrusor muscle is the primary muscle of the bladder wall responsible for bladder contraction during urination, and while it plays a role in the urinary process, it does not function as a sphincter. The pelvic floor muscles assist in supporting the bladder and contributing to continence but are not specifically designated as the involuntary muscle at the exit of the bladder.