Cardiac Conducting System

• Where does the heartbeat originate?

  In the heart itself
• What sets the rate at which the heart contracts?

  The auto-rhythmic cells of the sino-atrial node (SAN) or pacemaker, located in the wall of the right atrium
• What is the timing of the cardiac muscle cell contraction controlled by?

  Impulses from the SAN spreading through the atria, causing atrial systole
• Where do impulses from the SAN travel after atrial systole?

  The atrio-ventricular node (AVN), located in the centre of the heart
• Where do impulses from the AVN travel?

  Down fibres in the central wall of the heart and then up through the walls of the ventricles, causing ventricular systole
• What regulates the rate of the SAN?

  Medulla
• How is the SAN rate regulated?

  Through the antagonistic action of the autonomic nervous system (ANS)
• What increases heart rate?

  A sympathetic nerve releases the hormone noradrenaline
• What decreases heart rate?

  A parasympathetic nerve releases the hormone acetylcholine
• What does ECG stand for?

  Electrocardiogram
• What can an ECG detect?

  Impulses in the heart (they generate current, this is what is picked up by an ECG)