American Academy of Professional Coders (AAPC) Practice Exam

Which type of muscle is responsible for involuntary movements in hollow organs?

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle

4. Striated muscle

The correct answer is: Smooth muscle

Smooth muscle is the correct answer because it is specifically designed for involuntary movements within hollow organs such as the intestines, bladder, and blood vessels. This type of muscle operates automatically, without conscious control, allowing for functions like digestion, circulation, and the regulation of organ volume. Smooth muscle fibers are not striated, which distinguishes them from skeletal and cardiac muscles, both of which are striated. Additionally, skeletal muscle is under voluntary control, allowing for movements that are consciously performed, while cardiac muscle, although involuntary, is found specifically in the heart and is responsible for pumping blood. Striated muscle, a broader term, includes both skeletal and cardiac muscle but does not refer to the involuntary function of smooth muscle. Thus, smooth muscle's unique characteristics and functions make it the sole type responsible for involuntary movements in hollow organs.