Contractile Cell Phases

Question 1

Phase 4

“Restoration”

Answer 1

Restoring ions to RMP (-90mV) via Na+/K+ pump

Question 2

Phase 0

“Depolarization”

Answer 2

Depolarization (+30mV)
Influx of Na+
(Fast Na+ channels OPEN)

Question 3

Phase 1

“Early Rapid Repolarization”

Answer 3

Fast Na+ channels CLOSE

K+ efflux

Question 4

Phase 2

“Plateau Phase”

Answer 4

Slow repolarization
K+ efflux
Influx Ca++ & Na+ (SLOW Na+ channels open)
plateau in ionic charge

Question 5

Phase 3

“Final Rapid Repolarization”

Answer 5

Ca++ &Na+ Slow close

K+ efflux

Question 6

What causes the DELAY in the conduction at the AV node?

Answer 6

1. Smaller contractile fibers (diameter)
2. Fewer gap junctions
3. Fewer fast Na+ channels