Nernst equation

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Introduction:

  • If a cell membrane is freely permeable to an ion, the magnitude of potential difference for that ion at equilibrium is known as Equilibrium potential/ Nernst potential
  • Nernst potential can be calculated by Nernst equation (when there is no change in concentration of ions at equilibrium)
  • R= Gas constant, T=Absolute temperature, F=Faraday’s constant, Z=Valency, C1=Higher concentration, C2=Lower concentration
  • After putting all values at 37°C and considering valency = 1:

Question no 1:

Considering 2.8RT/F = 60, what will be the Nernst potential in the following picture?

Outer concentration of Cl- is higher, so Cl- from outside will enter inside the cell & make the inside of the cell more negative. So sign will be minus. So, answer will be: [-60 mV].

 

Question no 2:

Considering 2.8RT/F = 60, what will be the Nernst potential in the following picture?

Here inner concentration is higher, so K+ from inside will go outside & make the inside more negative. So, answer will be: [-60 mV].

 

Question no 3:

Considering 2.8RT/F = 60, what will be the Nernst potential in the following picture?

As valency of Ca++ is 2:

Inner concentration is lower, so Ca++ will enter the cell & make the inside of cell positive. So, answer will be: [+30 mV].

 

MCQ:

  1. Goldman Hodgkin Katz voltage equation/ Constant field equation is used to calculate resting membrane potential (RMP)
  2. K+ ion contributes maximally to the RMP
  3. Equilibrium potential for K+ ion is closest to RMP of nerve (-70 mV).

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