crista
Forum Guru
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On internal medicine rounds, the attending is reviewing the myocardial action potential. In which of the following phases of the action potential do the voltage-gated potassium channels begin to open?
A. Phase 0
B. Phase 1
C. Phase 2
D. Phase 3
E. Phase 4
i need an explanation,please.
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| usmleasr
Forum Guru
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Posts: 970
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phase 3...actually some k+efflx will be there during phase 1...but voltage gated k+channels open in phase 3..if i am wrong correct me
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| asmi
Forum Hero
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Posts: 4,609
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they begin to open in phase 1..
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| crista
Forum Guru
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Asmi, could you explain in few words what's happened in each fase, please.
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| kris2c
Forum Senior
Topics: 30
Posts: 108
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ACTION POTENTIAL OF A VENTRICULAR FIBER (FAST RESPONSE)
V-g=Voltage gated
Phase 0 - DEPOLARIZATION
• Increase Na+ Conductance
• Fast Na+ Channels (V-g) open during Depolarization--> quick Na+ influx
Phase 1 - Slight Repolarization
• Due to special K+ Channel: efflux through V-g K+ Channels
Phase 2 - Plauteau phase
• Slow (V-g) channels of Ca++ open; increasing Calcium conductance • Calcium influx occurs
o Participate in contraction
o Release additional Ca++ from Sarcoplasmic Reticulum
o Very low K+ conductance resulting in Delayed Repolarization and stable plateau (b/c V-g K+ Channels are closed; there is like an equilibrium : Ca influx and K efflux--> "Plateau" )
Phase 3 - Repolarization
• V-g Ca++ Channels close
• V-g K+ Channels REOPEN; increasing K+ conductance
• Massive K+ efflux
Phase 4 - Resting State 8)
In regular contracting ventricle fibers, we have a stable resting membrane potential (Em)
That's it :wink:
___________________
Kris2c
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| asmi
Forum Hero
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wow kris :icon_salut:
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| crista
Forum Guru
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thank you so much...
you save my nerves. 
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