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
• Describe the myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity

  1. Sinoatrial node (SAN) acts as pacemaker → releases regular waves of electrical activity across atria
  2. ○ Causing atria to contract simultaneously
  3. Non-conducting tissue between atria / ventricles prevents impulse passing directly to ventricles
  4. ○ Preventing immediate contraction of ventricles
  5. Waves of electrical activity reach atrioventricular node (AVN) which delays impulse
  6. ○ Allowing atria to fully contract and empty before ventricles contract
  7. AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue
  8. ○ Causing ventricles to contract simultaneously from the base up
• Where are chemoreceptors and pressure receptors located?

  Chemoreceptors and pressure receptors are located in the aorta and carotid arteries
• Describe the roles of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate - when there is a fall in blood pressure / rise in blood CO2 conc / fall in blood pH

  1. Baroreceptors detect [fall] in blood pressure and / or chemoreceptors detect blood [rise] in blood CO2 conc. or [fall] in blood pH
  2. Send impulses to medulla / cardiac control centre
  3. Which send more frequent impulses to SAN along [sympathetic] neurones
  4. So [more] frequent impulses sent from SAN and to / from AVN
  5. So cardiac muscle contracts [more] frequently
  6. So heart rate [increases]
• Describe the roles of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate - when there is a rise in blood pressure / fall in blood CO2 conc / rise in blood pH

  1. Baroreceptors detect [rise] in blood pressure and / or chemoreceptors detect blood [fall] in blood CO2 conc. or [rise] in blood pH
  2. Send impulses to medulla / cardiac control centre
  3. Which send more frequent impulses to SAN along [parasympathetic] neurones
  4. So [less] frequent impulses sent from SAN and to / from AVN
  5. So cardiac muscle contracts [less] frequently
  6. So heart rate [decreases]