Heart beat

• The heart

  A) sinoatrial node

  B) atrioventricular node

  C) Bundle of His

  D) Purkinje fibres

  
• Cardiac muscle does not tire
• Cardiac muscle is kept in check by the pacemaker (the sinoatrial node) which contracts slightly before everything else
• The heart is myogenic
• Myogenic- beats from within itself
• The heart beat

  1. A wave of electrical activity spreads from the SAN across both atria, and the atria contract
  2. A layer of non-conductive tissue prevents the wave crossing to the ventricles
  3. The wave passes through the AVN , between the atria (there is then a pause to allow blood to flow into the ventricle)
  4. AVN conveys an electrical wave between ventricles along the bundle of His
  5. Bundle of His conducts the wave through the septum to the base of the ventricles where it branches into purkinje fibres
  6. The wave is released from these fibres, causing ventricles to contract from the base upwards
• Medulla oblongata in the brain receives impulses from the spinal cord and sends out impulses to the heart
• Motor neurones (in the ANS) synapse with the SAN
• The autonomic nervous system controls involuntary responses
• The autonomous nervous system divides into the sympathetic and the parasympathetic nervous system
• Sympathetic- the 'fight/flight' response
• Parasympathetic- Return to normal