Controlling the heartbeat

• Label this diagram

  A) Sinoatrial node

  B) Atrioventricular node

  C) Bundle of His

  D) Bundle of HIs

  E) Purkinje fibres

  
• What does it mean that the heart is myogenic?

  Its contraction is initiated from within the heart itself and not from a nervous stimulation
• Where does the signal for contraction come from?

  The sinoatrial node
• How is the heartbeat started and regulated (pt 1)?

  1. Sinoatrial node sends waves of depolarisation over the atrial walls, so they contract (atrial systole)

  • there is a band of fibres between the atria and ventricles which have a high electrical resistance, so waves cannot spread from the atria to the ventricles

  2. Waves of depolarisation are passed onto the atrioventricular node. It delays the waves, allowing atria to complete contraction and the ventricles to fill
• How is the heartbeat started and regulated (pt 2)?

  3. The atrioventricular node passes excitation to the Bundle of His, then to the apex. This causes ventricles to contract from the apex upwards, so blood is pushed up to the arteries

  4. Excitation passes through Purkinje fibres and up through ventricle walls, so contraction begins at the apex
• Why is it important that waves of depolarisation are sent to the apex of the heart?

  It causes ventricles to contract from the base upwards, so blood is pushed up into arteries