HEART CONTROL

• A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises.

  • rate of respiration increases
  • CO2 conc increases
  • chemoreceptors in aorta/carotid arteries detect this
  • impulses sent to medulla
  • medulla sends impulses along sympathetic pathway to SAN
•  Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart.

  1. cardiac muscle
  2. av node
  3. along bundle of his/purkenye fibres
• cardiac muscle is myogenic
• SAN located in right atrium and acts as a natural pacemaker
• CONTROL PROCESS

  • SAN releases wave of depolarisation across atria causing it to conract
  • AVN releases another wave of depolarisation when the first has reached it
  • bundle of his conducts wave of depolarisation down septum and purkyne fibres
  • walls of ventricles then contract after a short delay whilst the AVN transmits second wave of depolarisation
  • This allows atria to pump blood back into ventricles
  • cells repolarise and cardiac muscle relaxes
• An increase in muscle activity causes an increase in heart rate (lines 12–14).

  Describe and explain how.

  inc in CO2 detected by chemoreceptors

  more impulses sent to medulla

  more impulses along sympathetic pathway

  to SAN