Q.The cardiac impulse is initiated and conducted further upto ventricle. The correct sequence of conduction of impulse is

The Heart's Own Electrical Wiring

Think of the heart as a pump that must beat in a precise, coordinated rhythm — top chambers (atria) first, then bottom chambers (ventricles). This rhythm isn't controlled by your brain; the heart has its own built-in electrical system that generates and spreads the signal to contract. That system is the cardiac conduction system.

The key idea: a small group of cells spontaneously fires an electrical impulse, which then travels along specialised pathways, forcing each part of the heart to contract in the correct order. No external trigger needed — the heart is self-starting.

The Components and Their Roles

The system consists of four main structures, arranged in sequence:

How the Impulse Travels

1. SA node fires — the impulse spreads across both atria via gap junctions in the atrial muscle cells. This causes the atria to contract (atrial systole).

2. Impulse reaches the AV node — here it is delayed by about 0.1 second. This delay is critical: it gives the atria time to empty their blood into the ventricles before the ventricles contract.

3. Impulse passes through the Bundle of His — this bundle splits into right and left branches that run down the interventricular septum.

4. Impulse spreads via Purkinje fibres — these fibres fan out from the bundle branches into the ventricular walls. They conduct the impulse extremely fast, so the ventricles contract almost simultaneously from the apex upward, squeezing blood out efficiently.

Why This Matters …