Atrioventricular bundle (bundle of His).

The cardiac conduction system is a collection of nodes and specialised conduction cells that initiate and co-ordinate contraction of the heart muscle.

Left bundle branch – conducts the impulse to the Purkinje fibres of the left ventricle.

Right bundle branch – conducts the impulse to the Purkinje fibres of the right ventricle.

It descends down the membranous part of the interventricular septum, before dividing into two main bundles: The atrioventricular bundle (bundle of His) is a continuation of the specialised tissue of the AV node, and serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles. The wave of excitation then passes from the atrioventricular node into the atrioventricular bundle. The AV node acts to delay the impulses by approximately 120ms, to ensure the atria have enough time to fully eject blood into the ventricles before ventricular systole.

Parasympathetic nervous system – decreases firing rate of the SA node, and thus decreases heart rate.Īfter the electrical impulses spread across the atria, they converge at the atrioventricular node – located within the atrioventricular septum, near the opening of the coronary sinus.

Sympathetic nervous system – increases firing rate of the SA node, and thus increases heart rate.

The rate at which the SA node generates impulses is influenced by the autonomic nervous system: The wave of excitation created by the SA node spreads via gap junctions across both atria, resulting in atrial contraction (atrial systole) – with blood moving from the atria into the ventricles. These pacemaker cells can spontaneously generate electrical impulses.

The sinoatrial (SA) node is a collection of specialised cells (pacemaker cells), and is located in the upper wall of the right atrium, at the junction where the superior vena cava enters. Components of the Cardiac Conduction System Sinoatrial Node

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