Involuntary muscle found inside many internal organs.

• A. Smooth muscle
• B. Cardiac muscle
• C. Skeletal muscle
• D. Myocyte

Answer: (A)

Muscle that contracts without conscious control and forms the walls of hollow organs is smooth muscle. It lines many internal structures such as the digestive tract, blood vessels, airways, bladder, and uterus, and can produce slow, sustained contractions that move contents along. The cells are spindle-shaped and non-striated, which is why this tissue lacks the visible banding seen in skeletal and cardiac muscle. Control comes from the autonomic nervous system and local signals rather than voluntary effort. In contrast, skeletal muscle is voluntary and striated, cardiac muscle is involuntary but only in the heart and also striated, and a myocyte is simply a muscle cell, not a tissue type. Therefore, the best fit for an involuntary muscle found inside many internal organs is smooth muscle.