 a.Sinoatrial node (SA node)  b.Atrioventricular node (AV node)  c.Atrioventricular bundle (AV bundle)  d.Right and left atrioventricular bundle branches  e.Purkinje fibers

 Located Junction of Superior Vena Cava  Specialized Pacemaker Cells  Intrinsic Rhythm- without stimulation by nerve impulses from brain and spinal cord  Initiates impulses at regular intervals

 From SA node to Contraction of both Atriums  Internodal Bundles- Right Atrium  Interartial Bundle- Left Atrium  Internodal Bundles to Atrioventricular node

 Av Node to Bundle of His (AV Bundle)  Left and Right Bundle Branches  Branches to Purkinje Fibers  Simultaneously Contract Ventricles

 SA node Intrinsic Rhythmical rate beats  What happens when SA node loses ability to initiate impulse?  Another Excitable Component takes over  Abnormal/ ectopic pacemakers AV Node or Purkinje Fibers Slower rate than SA Node AV Node beats per min

 Heart Conduction Animation Heart Conduction Animation  McGraw Hill McGraw Hill

 ECG (EKG)  a recording of the electrical activity (changes) during a cardiac cycle  How it works  Two Electrodes of Voltmeter  Passing of Action Potential between two electrodes

 P Wave – depolarization(+) of the atria (atrial contraction – systole)  SA Node  Atria  QRS Complex – depolarization of the ventricles (ventricular contraction, systole)  AV  Purkinje Fibers  T Wave – Repolarization(-) of the ventricles

 Cardiac Cycle is all the events associated with the blood flow through the heart during one complete heartbeat  Systole – contraction period of a chamber – ejection of blood.  Diastole – relaxation period of a chamber – filling of blood  Contraction (Eject) and Relaxation (Filling) ALWAYS follows electrical events seen in an ECG

 SA Node initiates action potential.  Atrial systole (1) causes Atrial pressure to increase, blood sent to ventricles through AV valve. (P Wave)  Ventricular Systole caused by impulse traveling down Bundle of His to Purkinje Fibers (QRS Wave)

 Isovolumetric Ventricular Contraction (2)  AV valves snap close causing the “Lubb” sound at the pressure rises in the ventricles  Ejection (3) of blood into pulmonary circuit  pressure in ventricle is greater than in the arteries so semilunar valves are forced open.  As pressure drops the Semilunar Valves snap close causing “Dubb” sound

 Isovolumetric Ventricular Relaxation (4)  Diastole begins, all valves closed. Once pressure has dropped low enough, the AV valves open and…..  Passive Ventricular Filling (5) because atrial pressure is higher than ventricle pressure. Toward the end of this period, atrial systole begins.

 Closing of the heart valves  Described as “Lubb – Dubb” Basic rhythm is lubb-dubb, pause, lubb-dubb, pause, lubb-dubb, pause.  First sound “Lubb” is the longest and loudest occurring when AV valves close.  Second sound “Dubb” is short, sharp sound occurring when Semilunar valves close.

 Sound is due to turbulence  Generally, heart murmurs indicate heart valve problem  “Swishing” sound indicates an incompetent valve - partially open valve after it should be closed so the blood backflows through the valve  High-pitched or click sound indicates a stenotic valve – the valve should be wide open, but it is not.