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#1
06-15-2011
 USMLE Forums Guru Steps History: Step 1 Only Posts: 343 Threads: 127 Thanked 525 Times in 192 Posts Reputation: 535
Nernst equation question

a 32 year old man is recovering from third-degree burns over 50% of his body surface area. His serum potassium is low(2.9mEq/L) which is common in healing burn victims.
He exhibits postural hypotension and skeletal muscle weakness. If Eq potential (nernst potential) for K+ in a nerve cell was -105mV and Eq potential for Na+ was +55mV.
What would be an approximate value for the resting membrane potential for a nerve cell in this man assuming normal membrane permeability..?

a)+80mV
b)+52mV
c)+22mV
d)-50mV
e)-98mV
f)-45mV

I know answer but don't know the explanation..so plz explain it simply..
AND IS THIS USUALLY MLE type QUESTION?
 The above post was thanked by: zeal7 (01-30-2013)

#2
06-15-2011
 USMLE Forums Master Steps History: 1+CK+CS Posts: 646 Threads: 52 Thanked 762 Times in 256 Posts Reputation: 773

-98mv...

characteristic of any cell is that the equilibrium potential is near to the potential of K+

so pick the answer closest to K+...

calculation in this condition is very difficult and complicated.. will only confuse u more.
 The above post was thanked by: Dr. Mexito (05-27-2012), INCOGNITO (06-16-2011), sami trailer (01-31-2013), usluipek (06-16-2011), zeal7 (01-30-2013)
#3
01-30-2013
 USMLE Forums Guru Steps History: Not yet Posts: 444 Threads: 109 Thanked 370 Times in 208 Posts Reputation: 380

nice que

#4
01-30-2013
 USMLE Forums Scout Steps History: Not yet Posts: 52 Threads: 1 Thanked 20 Times in 16 Posts Reputation: 30

hyokalemia... results in less + ions outside plasma membrane hence RMP becomes less negative since plasma membrane has ungated K ch , potassium ions will move out bringing RMP closer to equilibrium potential of K;
 The above post was thanked by: zeal7 (01-30-2013)

 Tags Cell-Biology-, Physiology-, Step-1-Questions

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