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* resting membrane potential
 #264111  
  proteus - 01/24/08 11:19
 
  The resting membrane potential is primarily determined by the intracellular and extracellular concentrations of which of the following?

A. Sodium
B. Potassium
C. Calcium
D. Phosphorous
E. Albumin

 
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* Re:resting membrane potential
#1140203
  hducri - 01/24/08 11:32
 
  b  
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* Re:resting membrane potential
#1140253
  drvirgo - 01/24/08 11:47
 
  b..  
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* Re:resting membrane potential
#1140657
  proteus - 01/24/08 14:52
 
  Choice (B) is the correct answer. Resting membrane potential is primarily determined by the intracellular and extracellular potassium concentrations. According a simplified version of the Nernst equation, the equilibrium potential for potassium (Em) equals the following:

Em = (-60 / Z) x log[Ki]/[Ko]

where Z is the charge on potassium, which is +1, Ki is the intracellular potassium concentration, and Ko is the extracellular potassium concentration. 98% of total body potassium is intracellular. The remaining 2% is extracellular. What this means is that small changes in extracellular potassium concentration results in dramatic changes in the membrane potential. In hyperkalemia, the extracellular potassium concentration increases, resulting in a less negative (more positive) membrane potential. In other words, the resting membrane potential becomes depolarized. This results initially in increased membrane excitability. With chronic depolarization, however, sodium channels become inactivated, resulting in decreased membrane excitability. Clinically, decreased membrane excitability results in weakness and cardiac arrhythmias. The other choices are incorrect
 
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