Which muscle type is striated and forms the walls of the heart?

• A. Cardiac muscle
• B. Skeletal muscle
• C. Smooth muscle
• D. Muscle fascicles

Answer: (A)

Cardiac muscle is the tissue that is striated and forms the walls of the heart. Its fibers are branched and connected at intercalated discs, which contain gap junctions and desmosomes that synchronize the heart's contractions across the whole myocardium. The striations come from the organized sarcomeres, just like in skeletal muscle, but cardiac muscle contraction is involuntary and regulated by the heart’s own conduction system and autonomic nerves. In contrast, smooth muscle is non-striated and lines the walls of hollow organs, and skeletal muscle is striated but forms muscles attached to the skeleton under voluntary control. Muscle fascicles are simply bundles of fibers within a muscle, not a distinct muscle type.