American Academy of Professional Coders (AAPC) Practice Exam

The correct choice identifies both cardiac and smooth muscles as types of involuntary muscle contractions.

Cardiac muscle is found exclusively in the heart and operates without conscious control. It is responsible for the rhythmic and automatic beating of the heart, which is essential for circulating blood throughout the body.

Smooth muscle, on the other hand, is located in the walls of hollow organs, such as the intestines, blood vessels, and the bladder. Like cardiac muscle, smooth muscle contracts involuntarily, enabling functions such as peristalsis in the digestive tract and regulating blood vessel diameter without conscious effort.

While skeletal muscle is under voluntary control, meaning it is consciously controlled to produce movement, the key feature of both cardiac and smooth muscles is their involuntary nature. This means they function autonomously as part of essential physiological processes, making the identification of both cardiac and smooth muscles as involuntary contractions accurate.