Final answer:
The detrusor muscle is part of the urinary bladder and is responsible for contracting to expel urine during urination.
Step-by-step explanation:
The detrusor muscle is part of the urinary bladder. The bladder is a hollow, muscular organ that collects and stores urine from the kidneys before elimination. The detrusor muscle is made of smooth muscle fibers and is responsible for contracting when urine needs to be expelled from the bladder. This muscle relaxes as the bladder fills with urine and contracts during urination to release urine into the urethra.