What structural feature causes the striated appearance of cardiac muscle under a light microscope?

• A. Regular arrangement of actin and myosin filaments into repeating sarcomeres
• B. Gap junctions that electrically couple neighboring cardiac muscle cells
• C. The presence of intercalated discs between adjacent cardiac muscle cells
• D. A high density of mitochondria packed between contractile fibers

Answer: (A)

Verified step by step guidance

1. Understand that the striated appearance in muscle tissue is due to the organized arrangement of contractile proteins within the muscle fibers.
2. Recall that actin (thin) and myosin (thick) filaments are arranged in repeating units called sarcomeres, which create a pattern of light and dark bands visible under a light microscope.
3. Recognize that cardiac muscle, like skeletal muscle, contains these sarcomeres, which are responsible for the striations observed.
4. Differentiate this from other features such as gap junctions and intercalated discs, which are important for cardiac muscle function but do not cause striations.
5. Conclude that the regular, repeating arrangement of actin and myosin filaments into sarcomeres is the structural feature causing the striated appearance of cardiac muscle.