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

• A. Skeletal Muscle
• B. Cardiac Muscle
• C. Smooth Muscle
• D. Visceral Muscle

Answer: (D)

The muscle responsible for lining the walls of hollow organs and operating without conscious control is smooth muscle. Smooth muscle fibers are non-striated and arranged in sheets that contract to move contents through organs (like peristalsis in the intestines) or to regulate the size of vessels. This involuntary action is controlled by the autonomic nervous system and various hormones, which is why you don’t have to think about these movements to keep them going. Some contexts refer to this tissue as visceral smooth muscle, emphasizing its location in the internal organs. In contrast, skeletal muscle is voluntary and striated, and cardiac muscle is involuntary but striated and found only in the heart. So the described tissue type is smooth muscle, often termed visceral smooth muscle when tied to the organs.