6.1.3 Control of the heart

• Cardiac muscle is myogenic - can contract / relax without receiving electrical impulses from nerves.
• Sinoatrial node (SAN) acts as pacemaker, sending regular waves of electrical activity across atria, causing atria to contract simultaneously.
• Non-conducting tissue between atria and ventricles prevents impulse passing directly to ventricles, preventing immediate contraction of ventricles.
• Waves of electrical activity reach atrioventricular node (AVN), delaying impulse, allowing atria to fully contract and empty before ventricles contract.
• AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where branches into Purkyne tissue, causing ventricles to contract simultaneously from base up.
• • Chemoreceptors and pressure receptors located in aorta and carotid arteries
  • Medulla oblongata in brain controls heart rate via the autonomic nervous system (2 divisions):
  • Sympathetic nerves → increase heart rate
  • Parasympathetic nerves → decrease heart rate
• Baroreceptors detect [fall / rise] in blood pressure and/or chemoreceptors detect blood [rise / fall] in blood CO, conc. or [fall / rise] in blood pH

  1. Send impulses to medulla / cardiac control centre
  2. Which send more frequent impulses to SAN along [sympathetic / parasympathetic] neurones
  3. So [more / less| frequent impulses sent from SAN and to / from AVN
  4. So cardiac muscle contracts [more / less] frequently
  5. So heart rate [increases / decreases]