Flashcards in Ions, Permeability and the Resting Membrane Potential Deck (13):
What are the three most important factors which determine the 'passive' movement of an ion across the membrane?
+ Electrical gradient
+ Concentration gradient
+ Membrane permeability
What is equilibrium potential?
When the electrical potential precisely offsets the tendency for K+ to diffuse down its concentration gradient (chemical potential difference)
What is the magnitude of the equilibrium potential?
The greater the chemical potential gradient ( conc. gradient) across a membrane, the greater the electrical gradient required to offset it
In the Nernst equation, what is R?
R = gas constant
In the Nernst equation, what is T?
T = absolute temperature
In the Nernst equation, what is F?
F = Faraday constant
In the Nernst equation, what is z?
z = valency
What does the Nernst equation prove?
That the equilibrium potential is proportional to the logarithm of the ratio of the concentrations in the two compartments.
What is the Nernst equation for a monovalent ion at 37°C?
Ex = 61 x log base10 x conc. of chamber 1 / conc. of chamber 2
What is the Nernst equation for a divalent ion at 37°C?
Ex = 30.5 x log base10 x conc. of chamber 1 (outside) / conc. of chamber 2 (inside)
What is the net difference between the distribution of Cl- ions and that of Na+ and K+ ions?
+ Cl- ions are passively distributed
+ According to the value of the membrane potential - intracellular Cl- ions concentration is set by the membrane potential
+ Na+ and K+ ion concentrations are maintained by the sodium pump and set the membrane potential
Why is the resting membrane potential a negative value?
Because K+ ions are not accompanied by anions, charge separation occurs and the electrical potential of the cell interior becomes negative with respect to the extracellular solution.