How are cardiac action potentials conducted in both nodal and non-nodal tissues?

• A. Through gap junctions only
• B. By cell-to-cell propagation
• C. Via extracellular diffusion
• D. By single fast conducting cells only

Answer: (B)

The key idea is that electrical impulses move through the heart by neighboring cells passing current to each other through gap junctions, making the tissue behave like a continuous syncytium. When a cell depolarizes, ions flow through gap junction channels into adjacent cells, triggering their depolarization and creating a wavefront that travels through both nodal (pacemaker) tissue and non-nodal (working myocardium) areas. This networked cell-to-cell propagation, not a single fast-conducting cell or extracellular diffusion, explains how the impulse spreads across the heart, albeit at different speeds in nodal versus non-nodal regions due to differences in gap junction expression and cell properties.