What type of muscle is involuntary and found in the walls of internal organs?

Smooth muscle is classified as involuntary muscle, meaning that it operates without conscious control. This type of muscle tissue is primarily found within the walls of internal organs such as the stomach, intestines, blood vessels, and bladder. Smooth muscle fibers are non-striated and can contract in a slow, sustained manner, allowing for various physiological functions like peristalsis in the digestive tract or regulation of blood flow in vessels.

In contrast to smooth muscle, cardiac muscle, while also involuntary, is exclusively found in the heart and is responsible for its rhythmic contractions. Skeletal muscle, on the other hand, is voluntary and enables movement of the skeleton; it is under conscious control. Striated muscle refers to the appearance of both skeletal and cardiac muscle under a microscope, but does not describe smooth muscle. Thus, the characteristics of smooth muscle accurately reflect its role and location within the body.