Question

______ keep(s) urine inside the bladder and ______ expel(s) urine from the bladder.

Group of answer choices

a. smooth muscle ; involuntary reflexes

b. skeletal muscles, involuntary reflexes

c. sphincter muscle; smooth muscle

d. smooth muscle; skeletal

e. skeletal muscle; skeletal muscle

Answer 1

Smooth muscle keeps urine inside the bladder and involuntary reflexes expel urine from the bladder.

Both the detrusor muscle and internal Sphincter is composed of smooth muscle. The detrusor muscle remains relax to allow the bladder to store urine. The internal sphincter remains contracted which help to keep urine from leaking.

The bladder (detrusor muscle & internal sphincter) is supplied by autonomic nervous system (sympathetic & parasympathetic nerves). When parasympathetic is stimulated, it cause detrusor muscle to contract and internal Sphincter to relax and thus there is expulsion of urine from the bladder. This is a involuntary reflex.

Since external Sphincter is composed of skeletal muscle and is under voluntary control of somatic nervous system so options (b), (d) & (e) are incorrect.

Option (c) is also incorrect since for expulsion of urine a reflex is needed which either contract/relax the smooth muscles to release urine from the bladder.

Thus the correct answer is (a) Smooth muscle, involuntary reflexes.