Question

Which of the following is smooth muscle?

1) internal urethral sphincter only
2) external urethral sphincter only
3) detrusor muscle only
4) both the internal urethral sphincter and detrusor muscle
5) both internal and external urethral sphincters

Answer 1

The internal urethral sphincter and detrusor muscle are smooth muscle, while the external urethral sphincter is skeletal muscle, thus option 4 is correct.

Step-by-step explanation:

The internal urethral sphincter and detrusor muscle are both made up of smooth muscle. Therefore, the correct answer is that both the internal urethral sphincter and detrusor muscle are smooth muscle (option 4). The internal urethral sphincter relaxes as the bladder fills, allowing urine into the urethra, while the detrusor muscle relaxes to accommodate more urine and contracts during urination to expel urine. In contrast, the external urethral sphincter is made of skeletal muscle, which is under conscious, voluntary control and is not a smooth muscle.