3.6.1.3 control of heart rate

• Coordinator is in the medulla of the brain
• Autonomic nervous system - Controls involuntary actions such as heart rate and breathing. The two branches work antagonistically
• Receptors in the walls of aorta and caroted arteries detect changes in blood pressure and pH (due to increased carbon dioxide concentrations)
• Parasympathetic nerve - slows heart rate

  Sympathetic nerve - increases heart rate
• Increase in blood carbon dioxide concentration:

  • More frequent action potentials to SAN along sympathetic nerve from medulla
  • SAN generates more frequent waves of electrical activity
  • increases heart rate
• Decrease in blood carbon dioxide concentration:

  • Less frequent action potentials from the medulla to the SAN along the parasympathetic nerve
  • Inhibits SAN, SAN generates less frequent waves of electrical activity
  • Heart rate decreases
• Blood pressure detected by baroreceptors:

  • High blood pressure = more APs along parasympathetic nerve
  • Low blood pressure = more frequent APs along sympathetic nerve
• Cardiac muscle is myogenic 


  Is able to generate its own electrical activity
• Electrical activity of the heart:

  1. The sino-atrial node generates a wave of electrical activity which spreads across the walls of the atria, causing them to contract
  2. A band of non-conducting tissue prevents the activity from spreading over the ventricles
  3. The activity reaches the atrioventricular node where it is delayed briefly to ensure the atria have fully contracted
  4. The activity passes down the bundle of his
  5. The activity then spreads across the walls of the ventricles up the purkinje fibres causing the ventricles to contract from the base upwards