heart rate

• • cardiovascular control centre located in medulla oblongata
  • controls the rate SAN generates electrical impulses
  • these impulses cause atria to contract thus determines rhythm of heartbeat
• changes act as stimuli

  • stimuli detected by baroreceptors(found in aortic and carotid bodies) and chemoreceptors(located in medulla oblongata and A/C bodies)
  • baroreceptors detect:blood pressure
  • chemoreceptors detect: PH, C02 levels, 02 levels
• neurones involved

  • once receptors are stimulated, send impulses to medulla which sends impulses to SAN along sympathetic or parasympathetic neurones- release different neurotransmitters which affect SAN in different ways

  sympathetic= increase rate SAN generates electrical impulses(increases HR)

  parasympathetic= decreases rate SAN generates electrical impulses(decreases HR)
• changes in HR- blood pressure

  high blood pressure CCC=cardiovacular control centre(in medulla)

  • detected by baroreceptors-CCC- impulse sent along parasympathetic neurones-acetylcholine(NT)
  • NT binds to receptors on SAN causing it to fire less frequently=reduced heart rate and BP back to normal
• changes in HR-blood pressure

  low blood pressure

  • baroreceptors detect-impulses to CCC-impulses sent along sympathetic neurones- noradrenaline released(NT)
  • NT binds to receptors on SAN causing it to fire more frequently
  • Heart rate increases and blood pressure increases back to normal
• changes in HR- blood conc.

  high blood 02, low c02 or high PH

  • chemoreceptors detect changes- sends impulses to CCC-sends impulses along parasympathetic neurones-acetylcholine released
  • NT binds to receptors on SAN
  • causing it to fire less frequently, HR slows and blood levels return to normal
• changes in HR- blood conc.

  low 02, high C02 , low PH

  • chemoreceptors detect changes- send impulses to CCC-impulses sent along sympathetic neurones- noradrenaline released
  • NT binds to receptors on SAN causing it to fire more frequently
  • HR speeds up and blood chemical levels return to normal