Conduction velocity of the cardiac impulse is fastest in the His-Purkinje system and slowest across the AV node. The structural basis for rapid impulse spread through ventricular myocardium is:
- A Gap junctions rich in connexin 43 linking adjacent myocytes electrically ✓
- B Abundant tight junctions between myocytes allowing cytoplasmic continuity
- C Desmosomal connections that transmit ionic current directly
- D Specialised autonomic nerve plexuses conducting the impulse along the epicardium
Correct answer: A. Gap junctions rich in connexin 43 linking adjacent myocytes electrically
Explanation
Ventricular myocytes are electrically coupled by gap junctions composed mainly of connexin 43, which allow direct ion flow between cells and produce near-syncytial behaviour. Conduction velocity is about 0.05 m/s in the AV node, deliberately slow to permit ventricular filling, and up to 2 to 4 m/s in Purkinje fibres. Desmosomes provide mechanical adhesion, not electrical coupling, and tight junctions are absent from working myocardium, eliminating options B and C.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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