Resting Membrane Potential Flashcards
Diffusion potential
Potential difference generated across the membrane because of a concentration difference of an ion
Potential difference in a normal mammalian nerve fiber
It’s about 94mV with negativity inside the fiber
What creates a membrane potential
Concentration difference of ions across a selectively permeable membrane under appropriate conditions.
Nernst potential
The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through a membrane
How is Nernst potential determined
By the ratio of concentrations of that specific ion on the outside and inside of the membrane using an equation called the Nernst equation. Greater the ratio greater is the tendency of ions to diffuse in one direction therefore greater Nernst potential required to prevent additional net diffusion.
Nernst equation
Calculate the Nernst potential for any univalent on at the normal body temp of 98.6 °F
EMF= +_ 61/z xlog( conc. Inside /conc. Outside)
z-electric charge of the ion
Nernst equation assumes that the potential in extracellular fluid remains at
0 potential.
Sign of the potential is +ve when
The ion diffusing from inside to outside is a - ve ion.
Sign of potential is - ve when
the ion diffusing from inside to outside is +ve
When membrane is permeable to several ions, diffusion potential that develops depends on 3 factors:
- Conc. Of the respective ions on the inside and outside of the membrane.
- Permeability of the membrane to each ion
- Polarity of the electrical charge of each ion
Goldman equation
Or the Goldman - hodgkins-Katz equation gives the calculated membrane potential inside the three membrane when it is permeable to several different ions.
How is membrane potential measured
A pipette filled with electrolyte solution is impaled through the cell membrane interior of the fiber. Another electrode called the “indifferent electrode” placed in the extracellular fluid, and the potential difference between the inside and outside is measured using a voltmeter. Rapid changes in the membrane potential during transmission of nerve impulse is recorded by an oscilloscope.
Voltage change area at the cell membrane is called
Electrical dipole layer
Normal resting potential inside the nerve fiber
Is - 90 mV
Na+ - K+ pump
An electrogenic pump, pumping 3 Na+ ions outside for each 2 K+ ions inside leaving a net deficit of positive ions on the inside causing a negative potential inside the cell membrane
Concentration gradient for sodium and potassium across the resting nerve membrane
Na+ (outside) : 142mEq/L
Na+ (inside) : 14mEq/L
K+ (outside) : 4mEq/L
K+ (inside) : 140mEq/L
Ratios of sodium and potassium ions from the inside to the outside are
Na+ ratio = 0.1
K+ ratio= 35.0
How does potassium leak into a resting cell
Through Channel Proteins called “tandem pore domain”, potassium channel or potassium leak channel.
It’s only potassium we’re the factor causing resting potential the resting potential inside the fiber would be
-94mV
If only sodium were a factor causing resting potential the resting potential would be
+61mV
According to Goldman equation the potential inside the membrane is
86mV which is near the potassium potential
How does Na+-K+ pump contribute to testing potential
The Continual kids of positive charges from the inside of the membrane creating an additional degree of negativity about, - 4mV
What contributed to membrane potential 90mV
The diffusion potentials alone caused by potassium and sodium diffusion would give a membrane potential of about 86mV
In addition -4mV is then contributed by the membrane potential by the acting electrogenic
Gibbs-donnan phenomenon
Inequitable distribution of diffusible one across the cell membrane because of the presence of non diffusible ions on one side. Many impermeant anions on the inside contribute to the negative charge inside the cell
