Exam qs

• When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay (2)

  • to allow atria to empty
  • before ventricles contract
• When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after the initiation of the heartbeat by the SAN (2)

  • Electrical activity only through Bundle of His / AVN
  • Wave of electrical activity passes over / through both ventricles at the same time
• Describe how a heartbeat is initiated and coordinated (5)

  • SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction
  • Non-conducting tissue prevents immediate contraction of ventricles / prevents impulses reaching the ventricles
  • AVN delays impulse whilst blood leaves atria / ventricles fill
  • AVN sends wave of electrical activity / impulses down the Bundle of His
  • Causing ventricles to contract from base up;
• The heart controls and coordinates the regular contraction of the atria and ventricles. Describe how. (5)

  • SAN → AVN → bundle of His / Purkyne fibres
  • Impulses / electrical activity (over atria)
  • Atria contract
  • Non-conducting tissue (between atria and ventricles)
  • Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract
  • Ventricles contract from the apex upwards
• Increased intensity of exercise leads to an increased heart rate. Explain how (3)

  • Carbon dioxide detected by chemoreceptors / pressure detected by baroreceptors
  • Medulla / cardiac centre involved
  • More impulses to SAN / along sympathetic nerve
• The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how. (5)

  • SAN initiates heartbeat / acts as a pacemaker / myogenic
  • SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction
  • AVN delays (electrical activity / impulses)
  • Allowing atria to empty before ventricles contract / ventricles to fill before the contract
  • AVN sends wave of electrical activity / impulses down Bundle of His / Purkyne fibres
  • Causing ventricles to contract (from base up) / ventricular systole
• The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node. (2)

  • Send out electrical activity / impulses
  • Initiates the heartbeat / acts as a pacemaker / (stimulates) contraction of atria
• Explain how nervous control in a human can cause increased cardiac output during exercise. (4)

  • Coordination via medulla (of brain) / cardiac centre
  • Increased impulses along sympathetic / cardiac accelerator nerve
  • To SAN / pacemaker
  • More impulses sent from SAN / pacemaker
• Explain why increased cardiac output is an advantage during exercise (3)

  • in exercise - more energy release for aerobic respiration
  • higher cardiac output - increases oxygen supply to muscles; Increases glucose supply (to muscles)
  • Increases CO2 removal (from muscles) / lactate removal; Increases heat removal (from muscles) / for cooling
• Explain how a rise in blood pressure results in a decrease in the rate of heartbeat (6)

  • baroreceptors in aorta / carotid arteries / carotid sinus
  • send impulses to medulla / cardio-inhibitory centre
  • impulses via parasympathetic nerves
  • to SAN
  • release of ACh / inhibits SAN / decreases impulses from SAN
  • decreases impulses to AVN
• Describe how an impulse reaches the base of the ventricles of the heart from the sinoatrial node (3)

  • it spreads through the atria
  • to the atrioventricular node
  • then through bundle of His/Purkyne fibres
• An increase in muscle activity causes an increase in heart rate. Describe and explain how (4)

  • increase in CO2 detected by chemoreceptors
  • send more impulses to cardiac centre / medulla
  • more impulses from cardiac centre / medulla along sympathetic pathway
  • to SAN