Which fibers spread action potentials through gap junctions to all ventricular cardiomyocytes, coordinating ventricular contraction?

• A. Purkinje fibers
• B. SA node
• C. AV node
• D. Fibrous skeleton

Answer: (A)

The spreading of the ventricular action potential through gap junctions to every cardiomyocyte to produce a synchronized ventricular squeeze is accomplished by the Purkinje fibers. These specialized conducting fibers form a fast, low-resistance network that runs through the subendocardial layer and connects to the ventricular muscle mass. Because they have abundant gap junctions and highly specialized conduction properties, Purkinje fibers transmit impulses rapidly throughout the ventricles, ensuring nearly simultaneous activation of all ventricle cells and a coordinated contraction. The SA node sets the pace, the AV node introduces a delay to optimize filling, and the fibrous skeleton mainly provides insulation and structural support rather than conducting impulses, so they do not spread the signal to the ventricular myocardium.