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.