6.1.3 control of heart rate

• cardiac muscle is myogenic, what does this mean

  it can contract and relax without receiving electrical impulses from nerves
• key areas of the heart for control of heart rate

  sinoatrial node (SAN)

  bundle of His

  atrioventricular node (AVN)

  purine tissue

  apex
• Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity

  1. SAN acts as a pacemaker

  2. SAN sends regular waves of electrical activity across atria

  3. Atria contract simultaneously

  4. Non-conducting tissue between atria/ventricles prevents impulse passing directly to ventricles

  5. Waves of electrical activity reach AVN

  6. AVN delays impulse, allowing atria to fully contract and empty before ventricles contract

  7. AVN sends waves of electrical activity down bundle of His

  8. Conducting wave between ventricles to apex

  9. Branches into purine tissue

  10. Ventricles contract simultaneously from base up
• where are chemoreceptors and pressure receptors located

  chemoreceptors and pressure receptors are located in the aorta and carotid arteries
• sympathetic neurones -> role of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate

  baroreceptors detect fall in blood pressure and/or chemoreceptors detect rise in blood carbon dioxide concentration or fall in blood pH

  sends impulses to medulla

  which send more frequent impulses to SAN along sympathetic neurones

  so more frequent impulses sent from SAN and to/from AVN

  so cardiac muscle contracts more frequently so heart rate increases
• parasympathetic neurone -> role of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate

  baroreceptors detect rise in blood pressure and/or chemoreceptors detect fall in blood carbon dioxide concentration or rise in blood pH

  sends impulses to medulla

  which send more frequent impulses to SAN along parasympathetic neurones

  so less frequent impulses sent from SAN and to/from AVN

  so cardiac muscle contracts less frequently so heart rate decreases