Spread of Excitation
  • Spread of Excitation 
    • SA node → atria → AV node → bundle of His → purkinje fibers → ventricle
  • cardiac action potential is initiated in myocardial cells in SA node 
    • spreads via gap junctions to myocardial cells of atria
  • a layer of fibrous, non-conducting tissue separates the atria and ventricles
    • consequently, cardiac action potential cannot spread directly from atria to ventricles
  • cardiac action potential spreads from atria to myocardial cells in AV node
  • cardiac action potential then spreads to bundle of His 
    • finally spreads to purkinje fibers that distribute action potential to ventricles
Conduction Velocity
  • Conduction velocity
    • bundle of His, purkinje fibers > atria > ventricles > AV node
  • slow conduction through AV node 
    • ensures that ventricles have sufficient time to fill with blood by contraction of atria 
    • before excitation and contraction to pump blood into systemic circulation



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