Key Terms
Atria (upper)
Receiving chambers; pump blood into ventricles Ventricles (lower): primary pumping chambers; propel blood into circulati
BLOOD FLOW PATH (full circuit)
Right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk → lungs (gas exchange) →
When ventricles contract
AV valves close (prevents backflow into atria); semilunar valves open (blood pushed into arteries) When ventricles relax
SA node
Sinoatrial node; located in the superior and posterior right atrium; highest inherent rate (80-100 bpm without neural in
Internodal pathways
Three bands (anterior, middle, posterior) carry the impulse from SA node to AV node; travel time approximately 50 ms; Ba
AV node
Atrioventricular node; located in the inferior right atrium within the atrioventricular septum; DELAYS the impulse appro
Bundle of His (AV bundle)
Carries impulse from AV node through the interventricular septum; splits into left and right bundle branches
Bundle branches
Left branch is larger (supplies the larger left ventricle); right branch connects to the moderator band, which carries i
Purkinje fibers
Spread impulse through the ventricular myocardium from the apex toward the base; fast conduction; full ventricular depol
Stable resting potential
About -80 mV in atria, -90 mV in ventricles
P wave
Atrial depolarization; atria begin contracting about 25 ms after
P wave starts QRS complex
Ventricular depolarization; atrial repolarization is buried inside this complex and masked; ventricles begin contracting
PR interval
From start of P wave to start of QRS; represents the time from atrial depolarization through the AV node to the start of
Ectopic focus
Area outside the SA node that initiates an impulse; can be caused by ischemia, drugs (caffeine, digitalis, acetylcholine
Systole
Contraction phase Diastole: relaxation and filling phase