Electrical System of the Heart

The role of the electrical system of the heart is:

• To maintain an adequate heart rate (proportional to the energy expenditure of the body)
• To coordinate the contraction of the atria and the ventricles in series
• To coordinate the simultaneous contraction of the two atria and subsequently the two ventricles (especially the ventricles)

Components of the electrical system in the heart

The Sino-Atrial (SA) Node:

• It is the command center for the coordination of all electrical activity
• The cells of the SA node have the property of automaticity (depolarizing spontaneously)
• These cells are under the influence of the autonomic nervous system
  • The sympathetic system (beta-adrenergic stimulation) increases the firing rate of the SA node
  • The parasympathetic system (acetylcholine stimulation) decreases the firing rate of the SA node

The Atrio-Ventricular (AV) Node:

• It serves as the gateway for electrical transmission between the atria and the ventricles
• It serves to insert an appropriate delay between atrial and ventricular contraction
• It prevents the ventricles from being activated too rapidly in cases of excessively rapid atrial activation

Bundle of His:

• A short segment of “electrical highway” connecting the AV node and the bundle branches

Bundle Branches:

• Left and right bundle branches deliver the electrical current from the bundle of His to the left and right ventricle, respectively

Purkinje Fibers:

• The bundle branches terminate in the myocardial tissue along the endocardium in Purkinje fibers