conduction system

The conduction system is the heart's internal wiring — the dedicated network of specialized tissue that generates each electrical impulse and ferries it to the right place at the right time. Ordinary heart muscle can pass the signal too, but slowly and clumsily; this system is the express network built to make a coordinated heartbeat possible.

It is best understood as a relay in sequence. The sinoatrial node fires, the impulse spreads across the atria, and it funnels into the atrioventricular node, where it is briefly delayed. From there it travels down the bundle of His, splits into the right and left bundle branches along the interventricular septum, and finally fans out through the Purkinje fibers into the ventricular muscle. The whole journey — from spark to full ventricular activation — takes only about a fifth of a second.

This careful sequence is what lets the atria contract first and the ventricles contract afterward, smoothly and in unison. A fault anywhere along the chain shows up as a recognizable problem: trouble at the node causes abnormal pacemaking, a block in the bundle branches widens the QRS complex, and a break at the atrioventricular junction produces heart block. The electrocardiogram is essentially a readout of this system at work.