Concept: The Cardiac Conduction System
This refers to the specialised system within the heart which ensures it contracts in a coordinated manner to give the most efficient pumping function. By initiating the heartbeat in a specialised pacemaker region which spontaneously generates Action Potentials, and then conducting the excitation along specialised networks which can either delay or accelerate the propagation, a uniform and controlled contraction can be maintained.
Illustration of the cardiac conduction system. Source: here (public domain) Attribution: OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]On each heartbeat, the following process occurs:
- The electrical excitation is initiated in the "sino-atrial node", the natural pacemaker, located near the top of the right atrium.
- The excitation is conducted along preferential pathways in the atria (the upper chambers of the heart) and down to the "atrio-ventricular node", the only electrical connection between the atria and ventricles .
- As excitation spreads throughout the atria, they contract and the ventricles fill with blood.
- Conduction is delayed in the atrio-ventricular node to allow time for the ventricles to fill.
- After this delay, excitation is conducted rapidly to the apex (the bottom) of the ventricles, through the bundle of His, before quickly spreading through the Purkinje Fibres throughout the ventricle. This supports near-simultaneous activation of the entire ventricular mass.
- The heart then undergoes repolarisation (returning to the non-excited state), allowing the atria and ventricles to fill in preparation for the next beat.