On electron microscopy of smooth muscle, small flask-shaped invaginations are seen along the sarcolemma, and electron-dense bodies are scattered in the sarcoplasm with similar dense plaques on the inner membrane. What is the functional significance of these structures?

• A Caveolae conduct action potentials and dense bodies synthesize contractile proteins
• B Caveolae store calcium and dense bodies anchor thin filaments for force transmission ✓
• C Caveolae form gap junctions and dense bodies store glycogen
• D Caveolae secrete extracellular matrix and dense bodies attach intermediate filaments only

Explanation

Smooth muscle lacks T-tubules; caveolae serve as subsarcolemmal sites for calcium handling. Dense bodies in the cytoplasm contain alpha-actinin and anchor actin thin filaments, while dense plaques on the sarcolemma transmit the generated force to the extracellular matrix. This arrangement allows contraction in multiple directions.

Reference: Junqueira's Basic Histology: Text and Atlas, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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