Certified Rehabilitation Registered Nurse (CRRN) Practice Exam

What is the function of the detrusor muscle?

1. Contracts the urinary bladder

2. Controls the sphincter

3. Facilitates urine storage

4. Regulates blood flow to the kidneys

The correct answer is: Contracts the urinary bladder

The detrusor muscle's primary function is to contract the urinary bladder. This smooth muscle surrounds the bladder and plays a crucial role in the process of urination. When the bladder fills with urine, stretch receptors in its wall signal the detrusor muscle to contract, which helps to expel urine from the bladder through the urethra. This contraction is an essential part of the micturition reflex, allowing for the voluntary or involuntary release of urine. In contrast, the other options describe functions or structures not associated with the detrusor muscle. While the sphincter muscles are involved in controlling the release of urine, they do not contract the bladder itself. Urine storage involves the bladder's ability to hold urine without actively contracting, a function that primarily relates to the bladder's elasticity and the surrounding supportive structures. The regulation of blood flow to the kidneys, on the other hand, is managed by the renal blood vessels and is not a function of the detrusor muscle.