Heart initiation and control

• Myogenic


  The heart will beat without any external stimulus
• Control of the basic heartbeat

  1. Sinoatrial node sends out a wave of excitation

  2. Atria contract

  3. Atrioventricular node sends out a wave of excitation

  4. Purkyne tissue conducts the wave of excitation

  5. Ventricles contract
• Sinoatrial node (SAN)


  • A group of cells in the wall of the right atrium
  • Initiates a wave of depolarisation that causes the atria to contract
• Atrioventricular node (AVN)


  • A region of conducting tissue between atria and ventricles
  • After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
• Bundle of His


  • A collection of conducting tissue in the septum (middle) of the heart
  • Divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
• Purkyne fibres


  • Spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart
• The ventricles contract and blood is forced out of the pulmonary artery and aorta
• The delay between atrial and ventricular contraction means that the ventricles contract after the atria
• The heart beats at around 60 times per minute
• The Annulus fibrosus is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles