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Flashcards in Cardiac Cycle and Sounds Deck (20)
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What is the slow action potential of the cardiac AP?

from the SA & AV nodes

influx of Ca2+


How are the fast and slow APs of the cardiac AP different?

fast AP due to Na+ influx into atrial & ventricular myocytes while slow AP due to Ca2+ influx @ SA/AV nodes


At what phase is the heart @ rest? (fast AP)

What gates are closed?

Phase 4

voltage gated Na+, K+ & Ca2+ channels are closed


What is open during phase 0 of fast AP?

depolarization: voltage gated Na+ channels open & cell


What is open during phase 1 of fast AP?

repolarization: Na+ channels inactivate & voltage gated K+ channels open (K+ will leave)


What is open during phase 2 of fast AP?

opening of Ca2+ channels that opposes leaving of K+ so membrane potential stabilized @ more + value


When does repolarization complete of fast AP?

Phase 3 (Ca2+ channels close, K+ channels still open)


What occurs during phase 4 of slow AP?

steady depolarization b/c opening of "funny" Na+ channels


What controls the heart rate?

changing how fast the funny Na+ channels open


Which cardiac tissue has the greatest number of funny Na+ channels?

SA node (heart pacemaker that is brought to threshold the fastest)


What is open during phase 0 of slow AP?

Ca2+ channels (Ca2+ influx is slower)


Which phase is not present in phase 1 of slow AP?

Phase 1 (repolarization)


What is the repolarization phase of the slow AP?

Phase 3 (efflux of K+)


On a normal ECG, what does the P wave represent?

atrial depolarization (from SA node depolarization)


On a normal ECG, what does the QRS complex represent?

phase 0 depolarization of ventricular myocytes

cells are depolarizing b/c influx of Na+


On a normal ECG, what does the T wave represent?

ventricular repolarization (efflux of K+)


What is the PR interval?

starts @ beginning of P wave & ends with start of QRS complex

time it takes for depolarization to pass from atria to ventricles via AV node


What most directly influences the PR interval?

slow conduction velocity of the AV node


What is the ST segment?

begins @ end of QRS complex & ends w/ start of T wave

assoc w/ phase 2 of fast AP (prolonged depolarization b/c Ca2+ influx into cell)


What is the QR interval?

starts w/ QRS complex & ends @ end of T wave

total time any ventricular myocites are depolarized