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

Cardiac muscle is the type of muscle tissue that is involuntary and specifically found in the walls of the heart. This specialized muscle tissue is unique in that it contracts rhythmically and continuously without conscious control, which is essential for maintaining the heartbeat and ensuring that blood is pumped throughout the body.

Cardiac muscle cells are striated, similar to skeletal muscle, but they are connected by intercalated discs that allow for coordinated contractions. This structure enables the heart to function effectively as a pump and is crucial for the synchronized contraction of heart chambers.

In contrast, skeletal muscle is voluntary and allows for conscious movement of the body. Smooth muscle, also involuntary, is found in the walls of hollow organs, such as the intestines and blood vessels, but it does not have the same striated appearance or function as cardiac muscle. Voluntary muscle typically refers to skeletal muscle, which is under conscious control. Therefore, the unique characteristics and specific location of cardiac muscle make it the correct answer in this context.