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Which of the following statements wrongly represents the nature of smooth muscle?
Intercalated discs (containing gap junctions and desmosomes) are the diagnostic signature of cardiac muscle fibres. Smooth muscles possess simple gap junctions and fusiform cells, never intercalated discs. Option (3) is false for smooth muscle!
Smooth muscle fibres are spindle-shaped (fusiform), unbranched, tapering at both ends, and strictly non-striated (unstriped) because their contractile myofilaments (actin and myosin) are not arranged in regular repeating sarcomeres. - They are involuntary and regulated by the autonomic nervous system. - They form the muscularis coat in the walls of internal visceral organs, including the stomach, intestine, urinary bladder, uterus, and blood vessels (tunica media).
- In smooth muscle, adjacent fusiform myocytes are bound together by loose connective tissue and communicate via simple gap junctions (nexus) across cell membranes. - In cardiac muscle, adjacent branched fibres are joined end-to-end by specialized zig-zag transverse thickenings called intercalated discs. These structures contain adherens junctions, desmosomes, and gap junctions that synchronize rapid electrical depolarization so the myocardium contracts as a functional syncytium. - Therefore, claiming that smooth muscle cells communicate via intercalated discs is factually wrong.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
This is a true statement for smooth muscle (they lack dark A-bands and light I-bands), so it cannot be the answer to "wrongly represents".
This is a true statement. Smooth muscles operate automatically without voluntary conscious control.
Correct as the false statement. Intercalated discs are strictly unique to cardiac muscle fibres, never smooth muscle.
This is a true statement. The tunica media of blood vessels is composed of concentric layers of smooth muscle.
Both smooth muscle and cardiac muscle utilize gap junctions for ion transfer. However, intercalated discs are complex mechanical and electrical junctional complexes found *only* at the junctions between cardiac myocytes.
"Intercalated discs are specialized junctions found exclusively in cardiac muscle, not smooth muscle."
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