questions 2

Ventricular Action Potential

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Topic updated on 09/03/17 12:26pm

Ventricular Action Potential; also Atria, Bundle of His, Purkinje Fibers
  • Resting membrane potential
    • inward rectifier K+ channels set resting membrane potential of cardiac myocyte at -90 mV; they are open at rest, close with depolarization, and open with repolarization.
  • Phase 0, upstroke 
    • cardiac action potential opens activation gates on voltage-gated Na+ channels and increases Na+ conductance
    • inward Na+ current depolarizes cell membrane of cardiac myocyte
    • cardiac myocyte cell membrane depolarization closes inward rectifier K+ channels
  • Phase 1, initial repolarization
    • cardiac myocyte cell membrane depolarization quickly closes inactivation gates on voltage-gated Na+ channels and decreases Na+ conductance
    • slow delayed rectifier K+ channels begin to open and K+ conductance increases
    • outward K+ current initiates cardiac myocyte cell membrane repolarization   
  • Phase 2, plateau 
    • plateau is a long period of relatively stable, depolarized cardiac myocyte cell membrane potential
    • L-type voltage-gated Ca2+ channels open and Ca2+ conductance increases
    • inward Ca2+ current balances outward K+ current
    • inward Ca2+ current induces release of Ca2+ from sarcoplasmic reticulum for excitation-contraction coupling (calcium-induced calcium release)
  • Phase 3, repolarization
    • slow delayed rectifier K+ channels open completely and K+ conductance further increases
    • L-type voltage-gated Ca2+ channels close and Ca2+ conductance decreases
    • outward K+ current exceeds inward Ca2+ current, repolarizing cardiac myocyte cell membrane
    • cardiac myocyte cell membrane repolarization opens rapid delayed rectified K+ channels and reopens inward rectifier K+ channels
  • Phase 4, resting membrane potential
    • slow delayed rectifier K+ channels and rapid delayed rectifier K+ channels close as cardiac myocyte cell membrane repolarizes to resting membrane potential
    • inward rectifier K+ channels reset and maintain membrane potential of cardiac myocyte at -90 mV
 


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(M1.CV.119) A 48-year-old female comes into the ER with chest pain. An electrocardiogram (EKG) shows a heart beat of this individual in Image A. The QR segment best correlates with what part of the action potential of the ventricular myocyte shown in Image B? Topic Review Topic
FIGURES: A   B        

1. Phase 0, which is primarily characterized by sodium influx
2. Phase 0, which is primarily characterized by potassium efflux
3. Phase 1, which is primarily characterized by potassium and chloride efflux
4. Phase 1, which is primarily characterized by calcium efflux
5. Phase 3, which is primarily characterized by potassium efflux

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