Control of Heart Rate

• Cardiac muscle is myogenic. What does this mean?

  It can contract and relax without receiving electrical impulses from nerves
• What acts as the pacemaker of the heart?

  Sinoatrial node (SAN)
• What does the SAN release across the atria?

  Regular waves of electrical activity
• What is the effect of the SAN's electrical activity on the atria?

  Causes atria to contract simultaneously
• What prevents the impulse from passing directly to the ventricles?

  Non-conducting tissue between atria and ventricles
• What is the consequence of the non-conducting tissue between atria and ventricles?

  Prevents immediate contraction of ventricles
• Where do the waves of electrical activity reach after the atria?

  Atrioventricular node (AVN)
• What does the AVN do to the impulse?

  Delays the impulse
• Why does the AVN delay the impulse?

  To allow atria to fully contract and empty
• What does the AVN send waves of electrical activity down?

  Bundle of His
• What happens to the wave of electrical activity at the apex?

  It branches into Purkyne tissue
• What is the result of the electrical activity reaching the Purkyne tissue?

  Causes ventricles to contract simultaneously
• What are the steps of myogenic stimulation of the heart?

  1. SAN releases electrical activity across atria
  2. Non-conducting tissue prevents impulse to ventricles
  3. AVN delays impulse for atrial contraction
  4. AVN sends activity down Bundle of His
  5. Activity reaches Purkyne tissue causing ventricular contraction
• Where are Chemoreceptors and Baroreceptors located?

  In the Aorta and Carotid arteries
• Describe the control of heart rate during exercise:

  • Muscle contraction
  • Therefore more aerobic respiration occurs
  • Therefore CO2 levels rise so pH decreases (acidity increases)
  • Chemoreceptors detect the change in pH and Baroreceptors detect the change in blood pressure
  • Action potentials are sent the the medulla oblongata
  • Medulla activates the cardioacceleratory centre (Sympathetic NS)
  • SAN produces more frequent action potentials
  • Heart rate and breathing increase
• Describe the control of heart rate during rest:

  • Muscles relax
  • therefore less aerobic respiration occurs
  • Therefore CO2 levels decrease increasing pH (acidity decreases)
  • Chemoreceptors detect the change in pH and Baroreceptors detect the change in blood pressure
  • Action potentials are sent to the medulla oblongata
  • Medulla activates the cardioinhibitory centre (parasympathetic NS)
  • SAN produces less frequent action potentials
  • Heart rate and breathing decreases