Which type of muscle is involuntary and found in internal organs?

Smooth muscle is indeed the type of muscle that is involuntary and primarily located in the walls of internal organs. This muscle type functions without conscious control, maintaining essential bodily functions. For instance, smooth muscle is responsible for regulating the movements of food through the digestive tract, controlling blood flow in blood vessels, and managing contraction and relaxation in the bladder.

In contrast, cardiac muscle, while also involuntary, is specifically found in the heart and has unique characteristics distinct from smooth muscle. Voluntary skeletal muscle, on the other hand, can be controlled consciously and is attached to the bones, facilitating movement of the skeleton. Striated muscle encompasses both skeletal and cardiac muscles, but the term does not specifically indicate involuntary function, which is a key characteristic of smooth muscle. Thus, smooth muscle is the correct answer as it perfectly aligns with the question's criteria of being involuntary and found in internal organs.