Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

Which type of muscle tissue is involuntary and found in the heart?

1. Cardiac muscle

2. Skeletal muscle

3. Smooth muscle

4. Striated muscle

The correct answer is: Cardiac muscle

Cardiac muscle is the correct type of muscle tissue that is involuntary and found specifically in the heart. This type of muscle tissue is distinct because it is responsible for the heart's pumping action, contracting without conscious control. The involuntary nature means that the heart operates automatically, regulated by the body's autonomic nervous system and intrinsic conduction system. Cardiac muscle cells are also unique in that they are striated, much like skeletal muscle, but unlike skeletal muscle, which can be controlled voluntarily, cardiac muscle functions independently of will. Additionally, it features intercalated discs, which allow for synchronized contraction, essential for effective heart function. Skeletal muscle, on the other hand, is primarily involved in voluntary movements of the body and is attached to bones. Smooth muscle is involuntary as well, but it is found in walls of hollow organs, such as the intestines and blood vessels, rather than the heart. Striated muscle is a broader term that encompasses both skeletal and cardiac muscle but does not specifically designate the involuntary function associated with cardiac muscle. Thus, the unique characteristics of cardiac muscle clearly identify it as involuntary and essential for heart function.