Action Potentials

Question 1

Myocardial action potential also occurs where?

Answer 1

Also occurs in bundle of His and Purkinje fibers.

Question 2

Phase 0 of Myocardial AP = ?

Answer 2

rapid upstroke and depolarization—voltage-gated Na+ channels open.

Question 3

Phase 1 of Myocardial AP = ?

Answer 3

initial repolarization—inactivation of voltage-gated Na+ channels. Voltage-gated K+ channels begin to open.

Question 4

Phase 2 of Myocardial AP = ?

Answer 4

plateau—Ca2+ influx through voltage-gated Ca2+ channels balances K+ ef ux. Ca2+ influx triggers Ca2+ release from sarcoplasmic reticulum and myocyte contraction.

Question 5

Phase 3 of Myocardial AP = ?

Answer 5

rapid repolarization—massive K+ efflux due to opening of voltage-gated slow K+ channels and closure of voltage-gated Ca2+ channels.

Question 6

Phase 4 of Myocardial AP = ?

Answer 6

resting potential—high K+ permeability through K+ channels.