igor999
Forum Senior
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A membrane with resting potential of -70 mv becomes what with an increase in extracellular K+ ions?
a) hyperpolarizes by 1-5 mm
b) hyperpoliarizes to 100 mm
c) depolarizes
d) no effect
An increase in extracellular K+ ions cause what?
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| black_horse
Forum Newbie
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I think an increase in extracellular K+ ions will have 3 effects:
1. a decrease in the conc. gradient of K+ across the cell membrane which will decrease K+ efflux.
2. more +ve ions outside the cell will increase the electric gr. across the cell membrane so increase Na+ influx.
This will lead to increase in cell excitability but won't elicit an AP.
So I think the best answer is C.
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| silver
Forum Guru
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why not hyperpolarized?
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| igor999
Forum Senior
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Black horse: I think you are wrong. I think it hyperpolarizes but I don't know if the resting potential is -70mV, if the excess Potassium that goes out leads to the resting potential to be like -75 to -80 mV or if it hyperpolarizes it completely to -100 mV.
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| black_horse
Forum Newbie
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You said extracellular K+, that means less K+ will actually go out, and RMP will definitly depolarize (may be to firing level, this what I may be wrong in).
you are confused with these 2 choices coz they are distractors.
I found this thread
http://www.prep4usmle.com/forum/thread/29675, hope it helps.
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| new_n_lost
Politically InCorrect
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yes Black Horse is right the RMP is largely based upon the Intracellular Conc of K ions and the lack of Potassium ions extracelluarly leads to a conc. gradient. Remember that we have Ungated Potassium Channels where the K ion slowly diffuses outside and then there is the Na K ATPase pump which restores the K conc inside the cell. If the Conc Gradient of K ion is reduced i.e there is More Of K ion extracellularly then the RMP becomes more positive.
This is a a very tricky concept to understand in order to simplify here it is : THE Conc Gradient Difference Across the Membrane of the K ion Dictates the RMP. In Settings of Hyperkalemia where the Increase of Extracellular K ion is not due to the Relatively Uncommon Intracellular Shift of K ( DKA) the Excess K ion will lead to decrease RMP towards the Threashold for AP thus making the Tissue more Excitable but the AP Spike is lowered as the Conc of K and Na ions is altered. In setting of Prolong Hyperkalemia the RMP Equals the AP Threshold and the Paralysis occurs.
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| igor999
Forum Senior
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thanks for explanation
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