Which of these muscles is classified as involuntary?

Cardiac muscles are classified as involuntary muscles because they operate without conscious control. This type of muscle is found only in the heart and is responsible for the rhythmic contractions that pump blood throughout the body. The involuntary nature of cardiac muscles means that they are regulated by the autonomic nervous system, allowing the heart to beat continuously and automatically, adjusting to the body's needs without requiring conscious thought.

In contrast, skeletal muscles are considered voluntary since they can be consciously controlled to produce movement, and voluntary muscles refer to those that are under conscious control, which primarily consist of skeletal muscles. The option stating "All of the above" is incorrect because it implies that all mentioned muscle types are involuntary, which is not true for skeletal muscles that require conscious effort to function. Thus, the classification of cardiac muscles as involuntary accurately reflects their unique and essential role in the circulatory system.