Which node is responsible for delaying conduction to allow atrial contraction before ventricular contraction?

Which node is responsible for delaying conduction to allow atrial contraction before ventricular contraction?

• A. SA node
• B. AV node
• C. Purkinje fibers
• D. Bundle of His

Answer: (B)

The key idea is the gatekeeper role of the atrioventricular (AV) node in coordinating the timing between atrial and ventricular contractions. The AV node sits between the atria and ventricles and deliberately slows the electrical impulse as it passes from atrial tissue to the His-Purkinje system. This brief delay gives the atria time to contract and complete ventricular filling (the atrial kick) before the ventricles start to contract. That slower conduction comes from the AV node’s cellular properties: fewer gap junctions, smaller pathways, and a longer refractory period, all of which slow the signal. Once the impulse makes it through the AV node, it travels quickly through the bundle of His and Purkinje fibers to activate the ventricles in a coordinated, synchronized manner. In contrast, the SA node drives the heart rate but does not delay conduction; the Purkinje fibers rapidly distribute the impulse through the ventricles; and the bundle of His mainly serves as a conduit from the AV node to the ventricles. The delaying function specifically belongs to the AV node.

The key idea is the gatekeeper role of the atrioventricular (AV) node in coordinating the timing between atrial and ventricular contractions. The AV node sits between the atria and ventricles and deliberately slows the electrical impulse as it passes from atrial tissue to the His-Purkinje system. This brief delay gives the atria time to contract and complete ventricular filling (the atrial kick) before the ventricles start to contract.

That slower conduction comes from the AV node’s cellular properties: fewer gap junctions, smaller pathways, and a longer refractory period, all of which slow the signal. Once the impulse makes it through the AV node, it travels quickly through the bundle of His and Purkinje fibers to activate the ventricles in a coordinated, synchronized manner.

In contrast, the SA node drives the heart rate but does not delay conduction; the Purkinje fibers rapidly distribute the impulse through the ventricles; and the bundle of His mainly serves as a conduit from the AV node to the ventricles. The delaying function specifically belongs to the AV node.