.6 Heartbeat

• high bp is detected by baroreceptors, impulses sent from medulla along parasympathetic neurones to the SAN >acetylcholine is released then heart rate slows down and bp decreases
• Sympathetic- fight or flight
• Parasympathetic- rest + digest
• atrioventricular node

  • waves of electrical activity pass from the atria to a collection of non-conducting tissuethis creates a delay to ensure the atria are empty before the ventricles begin to contract
  • the electrical activity passes through the AVN to bundle of His
  • bundle of His is a collection of conducting tissue that transmits the electrical activity to the apex (bottom) of the heart and around the ventricle walls along fibres called the Purkyne fibres
• Contraction of ventricles:

  as waves of electrical activity pass along the purkyne fibres, the ventricles contract together

  blood is forced out of the ventricles and out of the heart
• the heart is myogenic so it initiates its own contraction within the muscle wall
• contraction of atria

  • electrical waves from SAN cause the right and left atria to contract together
  • this forces blood in the right atrium into the right ventricle and blood in the left atrium into the left ventricle
• sinoatrial node

  • walls of right atrium
  • acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals
• Baroreceptors-

  sensitive to change in blood pressure

  if bp increases, heart rate increases

  found in the walls of various arteries but particularly in the carotid sinus (wall of carotid artery)
• Chemoreceptors-

  sensitive to change in CO2 concentration

  if CO2 is high heart rate increases

  found in the aortic body, in the wall of the aorta

  found in the carotid body, in the wall of the carotid artery in the neck