Cardiac Cycle and Sounds Flashcards
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+
