control of heart rate

• How does increased blood pressure lead to decreased heart rate?

  • Baroreceptors in walls of carotid arteries and the aorta detect the change in blood pressure
  • Medulla oblongata receives the increased frequency impulses from the baroreceptors regarding the increase of blood pressure 
  • Decreasing the frequency of action potentials down sympathetic neuron
  • This leads to a decrease in heart rate, mediated by SAN 
• How does autonomic nervous system respond during exercise:

  1. Blood has a higher concentration of carbon dioxide, and so a lower pH.
  2. Chemoreceptors in the carotid arteries detect this and increase the frequency of impulses sent to the medulla oblongata.
  3. The medulla oblongata increases the rate of impulses to the SAN via the sympathetic nervous system.
  4. Heart rate increases.
  5. This provides the extra oxygen required for increased respiration in active muscles.
  6. The increased blood flow also helps remove excess carbon dioxide via the lungs.
  7. Carbon dioxide concentration reduces.
• • Cardiac muscle is Myogenic - it contracts on its own accord, but the rate of contraction is controlled by a wave of electrical activity
• • The sinoatrial node (SAN) is located in the right atrium, known as the pacemaker - stimulates atria to contract
• • The atrioventricular node (AVN) is located near the boarder of the right and left ventricle within the atria still - picks up electrical activity from SAN
• The bundle of His runs through the septum- receives electrical activity from AVN, conducting wave of excitation to the base of heart
• The purkyne fibres are in the walls of the ventricles - conductive tissue
• How is the cardiac cycle controlled by the SAN and AVN?

  • SAN initiates heartbeat, acting as a pacemaker
  • SAN sends wave of electrical activity across atria causing atrial contraction 
  • AVN delays electrical impulses 
  • Allows atria to empty before ventricles contract 
  • AVN sends wave of electrical activity down bundle of His/Purkyne fibres 
  • Causing ventricles to contract from the base up 
• impulses sent by sympathetic nervous system for chemoreceptors and by parasympathetic nervous system for barorceptors