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nmdcat.online July 28, 2026

In biological comparisons, the presence of striations is a key histological marker. What is the fundamental molecular reason for the lack of striations in smooth muscle?

A. Smooth muscle completely lacks myosin and actin filaments
B. The actin and myosin filaments are not organized into repeating sarcomeres
✓
C. Smooth muscle utilizes calmodulin instead of troponin
D. The thick filaments in smooth muscle lack myosin heads

📝 Explanation

Smooth muscle does contain actin and myosin, and they slide against each other to cause contraction. However, these filaments are not arranged in the highly ordered, repeating, registered units (sarcomeres) that create the alternating light and dark bands (striations) seen in skeletal and cardiac muscle.

📖 Additional Information

  • Smooth muscle completely lacks myosin and actin filaments
  • The actin and myosin filaments are not organized into repeating sarcomeres
  • Smooth muscle utilizes calmodulin instead of troponin
  • The thick filaments in smooth muscle lack myosin heads

Smooth muscle does contain actin and myosin, and they slide against each other to cause contraction. However, these filaments are not arranged in the highly ordered, repeating, registered units (sarcomeres) that create the alternating light and dark bands (striations) seen in skeletal and cardiac muscle.

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