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nmdcat.online July 28, 2026

The functional relationship between T-tubules and the sarcoplasmic reticulum (SR) is critical for excitation-contraction coupling. In which muscle type is this structural relationship the least developed or entirely absent?

A. Skeletal muscle
B. Cardiac muscle
C. Smooth muscle
✓
D. Striated muscle

📝 Explanation

Smooth muscle lacks true T-tubules and has a poorly developed sarcoplasmic reticulum. Instead of T-tubules, it has small invaginations of the sarcolemma called caveolae, which concentrate extracellular calcium necessary for contraction.

📖 Additional Information

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
  • Striated muscle

Smooth muscle lacks true T-tubules and has a poorly developed sarcoplasmic reticulum. Instead of T-tubules, it has small invaginations of the sarcolemma called caveolae, which concentrate extracellular calcium necessary for contraction.

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