Resting Potential Flashcards
Write the Nernst equation, and explain the effects of altering either the intracellular or extracellular Na+, K+, Cl-, or Ca2+ concentration on the equilibrium potential for that ion
Ex = (58/z)log([xo]/[xi])
Ex = equilibrium or resting potential across the membrane z = valence; 1 for K, 2 for Ca, -1 for Cl [x1] = concentration of x in vessel 1 (same for [x2])
Also, use the equation logically–I know the answer should be negative for K+
Using the Goldman equation, explain how the relative permeabilities to Na+,K+,and Cl- create a resting membrane potential
The Goldman equation is not an equilibrium potential, it is a STEADY STATE potential.
Vm = 58log([K]o + a[Na]o)/(K]i + a[Na]i)
or
Vm = 58log(pK[K]o + pNa[Na]o)/(pK[K]i + pNa[Na]i)
a = permeability Na/ permeability K
p = permeability
You can keep adding ions, but for anions you must invert the outside and inside concentration
Membrane potential equation, M =
Q/V (coulombs/ volts)
Remember that resting membrane potential is a steady state potential!
Reduction in charge
Depolarization = more positive
Increase in charge
Hyper polarization = more negative
Are Na, Cl, K, & Ca mainly intracellular or extracellular?
Na, Cl, & Ca are extracellular, & K is intracellular
Membrane of resting neuron is more permeable to ____ than to any other ion?
K+ (Potassium)
Explain what would happen to a patient with low levels of K+ in the plasma (Hypokalemia).
Hypokalemia, or reduced extracellular K+ concentrations, enhances the electrochemical gradient favoring K+ efflux from cells and causes the K+equilibrium potential to shift negative. Because membrane potential is determined largely by the transmembrane K+ gradient, resting membrane potential (Vm) would shift negative also.
A negative shift in Vm means that a stronger depolarization would be necessary to take Vm to the threshold for voltage-gated Na+ channel activation, but, once reached, an action potential would be initiated.
The resting potential of a myelinated nerve fiber is primarily dependent on the concentration gradient of which of the following ions?
K+
The resting potential of any cell is dependent on the concentration gradients of the permeant ions and their relative permeabilities (Goldman equation). In the myelinated nerve fiber, as in most cells, the resting membrane is predominantly permeable to K+. The negative membrane potential observed in most cells (including nerve cells) is due to the relatively high intracellular concentration and high permeability of K+.
If a cell membrane is permeable only to K+, how will this affect the resting potential?
Because this membrane is permeable to only K+, its resting membrane potential will equal the K+ equilibrium potential (EK).
EK is determined by the activity gradient for K+ that exists between the extracellular and intracellular fluids. It is the transmembrane potential that would occur when the net flux of K+ across the membrane equals 0 if the cell membrane were permeable only to one ion, K+ We can estimate EK by using the Nernst equation.
Remember that the concentrations of K+ are NOT the same inside & outside @ the equilibrium potential.
Select the mechanism most responsible for the production of the resting transmembrane potential in an axon; is it the NaKATPase or the permeability of the membrane?
The Na+/K+ pump potential is only a small part of the resting potential.
The Na+/K+ pump and differential permeability of the plasma membrane are both responsible for the resting transmembrane potential. Consistent with the pump hypothesis is the generally accepted conclusion that an active transport system extrudes 3 Na+ from the cell for every 2 K+ carried into the cell. Consistent with the permeability hypothesis is the conclusion that the plasma membrane during its resting potential is more permeable to K+ than to Na+.
When using the nernst equation, know that if the intracellular concentration = extracellular concentration, then the equilibrium potential =
0, since log(1) = 0
