Ventricular action potential

Question 1

Ventricular action potential can also occur in

Answer 1

Bundle of His and Purkinje fivers

Question 2

Phase 0

Answer 2

Rapid stroke,

voltage gated Na+ channel opens

Question 3

Phase 1

Answer 3

Initial repolarization
Inactivation of voltage gated Na+ channel
Voltage gated K+ channels begin to open.

Question 4

Phase 2

Answer 4

Plateau - Ca2+ influx through voltage-gated Ca2+ channels balances K+ efflux

Ca2+ influx triggers Ca2+ release from SR and myocyte contraction

Question 5

Phase 3

Answer 5

Rapid repolarization

Massive K+ efflux due to opening of voltage gated slow K+ channel and closure of voltage gated Ca2+ channels.

Question 6

Phase 4

Answer 6

Resting potential

High K+ permeability through K+ channel

Question 7

In contrast to skeletal muscle

Answer 7

Cardiac muscle AP has a plateau; due to Ca2+ influx and K+ efflux.

Cardiac nodal cell spontaneous depolarize during diastole resulting in automaticity due to If channels (slow mixed Na+/K+ inward current)