In cardiac muscle histology, intercalated discs are found at the Z-line level. Which specific junctional complexes within the intercalated disc transmit mechanical force and synchronise electrical excitation respectively?

• A Fascia adherens (transmits contractile force) and gap junctions/nexus (synchronise electrical excitation); desmosomes provide structural cohesion ✓
• B Gap junctions transmit force; tight junctions (zonula occludens) synchronise electricity
• C Desmosomes transmit force; T-tubules synchronise excitation
• D Fascia adherens transmit both force and electrical signals; no separate electrical junction needed

Explanation

Intercalated discs have a complex three-component structure: (1) Fascia adherens — the largest component; anchors sarcomeric actin filaments to the plasma membrane via alpha-actinin and vinculin; mechanically couples adjacent cells so contractile force is transmitted. (2) Desmosomes (maculae adherentes) — link intermediate filaments (desmin) across the junction; provide structural cohesion to prevent cell separation during powerful contractions. (3) Gap junctions (nexus/connexons, made of connexin 43 in ventricles) — low-resistance intercellular channels that allow direct ionic current flow, synchronising electrical excitation throughout the cardiac syncytium. Mutations in desmoplakin and plakophilin-2 (desmosome proteins) cause arrhythmogenic right ventricular cardiomyopathy (ARVC).

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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