Myogenic Coordination of the Heartbeat

• Node Diagram

  A) Sino-atrial node

  B) right atrium

  C) Atrioventricular node

  D) septum

  E) atria

  F) ventricles

  G) Bundle of His

  H) septum

  I) purkinje fibres

  J) septum

  K) apex of

  L) ventricles

  M) apex of ventricles

  
• Myogenic Coordination of Atrial Systole

  • Cardiac cycle coordinated by electrical activity in specialised tissues in cardiac muscle
  • Called myogenic as it automatically contracts and relaxes
  • Sinoatrial node (SAN)
  • Sarts excitation wave coordinating cardiac cycle (‘pacemaker’)
  • Wave spreads over muscular atria walls, causing atrial systole
  • Synchronised; contract almost at same time
  • Excitation wave from SAN reaches atrioventricular node (AVN)
  • Time delay (0.12s) ensures atria contract fully
  • All blood moved from atria to ventricles
• Myogenic Coordination of Ventricular Systole

  • Non-conductive tissue band between atria and ventricles stops wave passing to ventricle walls
  • Ventricles fill with blood before contracting
  • Wave spreads from AVN
  • Down septum, in Bundle of His (made of Purkinje fibres), to apex
  • Up through Purkinje fibres in ventricle cardiac muscle walls, causing contraction from apex up
  • Ventricles contract together, pushing blood into pulmonary circulation (right) and systemic circulation (left)