ELECTRICAL CONDUCTION

• Electrical Conduction - Fast Action Potential (non-pacemaker cells)

  • Autorhythmic cells of the heart generate an electrical signal which travels along a conduction pathway, to ensure coordinated contraction of the heart.
• The electrical signal is a cardiac action potential. An action potential involves a rapid and short lasting rise in electrical potential, then a fall in the electrical potential. This is the result of the opening and closing of channels in the membrane, which acutely change the membrane permeability to different ions.
• 1. Sinoatrial (SA) node

  • primary pacemaker (allows the production of action potential which leads to the contraction of heart)
  • Located in the right atria, medial to the opening of the superior vena cava. 
  • Intrinsic rate: 60 to 100 bpm (normal heart rate)(means that it can cause contraction at this rate)
  • Conduction velocity: 0.5 m/sec
  • Controlled by the sympathetic and parasympathetic nervous systems.
• 1. Atrioventricular (AV) node

  • Gatekeeper
  • causes delay
  • Located medial to the right atrioventricular valve.
  • Intrinsic rate: 40 to 60 bpm 
  • Conduction velocity: 0.02-0.05 m/sec
  • The propagation delay allows atrial contraction to be completed, and the ventricles to fill with blood before ventricular contraction begins.
• Myocardial Infarction (Heart Attack):

  • Decreased blood flow to the heart, often due to plaque buildup, can block the right coronary artery, leading to a heart attack.
  • This can damage the SA node, the heart's primary pacemaker.
  • If the SA node fails, the AV node can take over, but it results in a slower heart rate.
  • If the AV node also fails, the Bundle of His and bundle branches will control the heart rate, but it will be much slower and less effective in maintaining homeostasis.
• Bundle of His and Left and right bundle branches

  • Located at the interventricular septum. The branches descend to the apex of each ventricle. 
  • Intrinsic rate: 20 to 40 bpm 
  • Conduction velocity: 1-2 m/sec
• Purkinje fibers

  • Diffuse network of conducting strands located beneath the ventricular endocardium.
  • Intrinsic rate: 20 to 40 bpm 
  • Conduction velocity: 2-4 m/sec