Ionic Distributions and Nernst Equation Flashcards
What creates a diffusion potential
concentration difference of an ion across a selectively permeable membrane
what is another name for diffusion potential
membrane potential
what way do molecules move in terms of energy
from high energy to low energy
what kinds of forces create the energy that drive the movement of molecules
chemical
electrical
electrochemical
when a molecule exists in a different concentration on either side of the membrane, there is what across the membrane
concentration gradient
what symbol symbolizes the difference in concentration
∆C
what is the name of the net force driving molecules down a concentration gradient
chemical driving force
chemical driving force is directly proportional to what
concentration gradient
the greater the concentration gradient, the greater the
force
if there is more than one molecule across a membrane, describe their concentration gradients/driving force
they each have their own
when molecules move from area of high concentration to an area of low it results in
release of energy
when molecules release energy by going to lower concentration it is described as
going down concentration gradient
ions, atoms or molecules w/ charge are affected by what force
electrical driving force
if there is no concentration gradient but there are differently charged ions, there will still be
electrical driving force, still have movement of ions
membrane potential results from
unequal distribution of charges across the membrane
if anions and cations are balanced across the membrane, what is the membrane potential
0
what is the unit the membrane potential is measured in
mV
what does mV stand for
one thousandth of a volt (mili volt)
what is membrane potential for most cells
-70 mV
in resting cell, cations are attracted to
inside of cell
in resting cell anions are attracted to
exterior of cell (outside)
magnitude of electrical force depends on what
size of membrane potential
charge of the ion
size of membrane potential & charge of ion determine what
magnitude of electrical force
the greater the membrane potential or charge of the ion, the greater the
electrical driving force
define the electrochemical driving force
total forces acting upon ions, combining chemical and electrical forces
the net direction of electorchemical force =
sum of both forces
the point at which the chemical and electrical forces (if they are going opposite direction) equal each other is the
equilibrium potential
what does the equilibrium potential of an ion depend on
concentration gradient
valence (charge)
Eion stands for
electrical potential difference
The electrical potential difference (Eion) across the membrane required to oppose the concentration force exactly to prevent net diffusion of an ion is called the
Nernst or equilibrium potential for that ion.
what is the nernst equation (write both versions)
delta u(x) = RTln[X]A + zF(EA - EB)
[X]B
Eion (mV) = 60 log Co **THIS IS THE ONE TO KNOW
z Ci
what is the nernst equation used to determine
equilibrium potential of an ion
What does R stand for in nernst equation
gas constant
what does T stand for in nernst equation
absolute temperature
what does XA stand for in nernst equation
concentration of ion X on side A
What does XB stand for in nernst equation
concentration of ion X on side B
what does z stand for in nernst equation
valence of ion
What does F stand for in nernst equation
Faraday’s constant
what does EA-EB stand for in nernst equation
electrical potential
what does ∆u stand for in nernst equation
electrochemical potential difference (net force on ion)
when chemical and electrical gradients are equal and opposite, ∆u=?
it is said to be in
0
electrochemical equilibrium!
What does Co = in nernst equation?
concentration of ion outside of cell
what does Ci = in nernst equation?
concentration of ion inside cell
If the chemical and electrical forces are in opposite directions and the equilibrium potential > the membrane potential
the chemical force is larger and the combined electrochemical force is in the direction of the chemical force.
If the chemical and electrical forces are in opposite directions and the membrane potential > equilibrium potential
the electrical force is larger and the electrochemical force is in the direction of the electrical driving force
draw diffusion potential b/w nerve fiber A and B and explain
pg 3 ppt
if we were at -94 at nerve fiber A (only permeable to potassium) with no net current, change the electrical driving force (not chemical) to -120 (making membrane potential more neg compared to outside) will there be net current
if there is net current, what direction would potassium move
yes - b/c driving force is a different magnitude from chemical driving force
inward potassium current b/c potassium is attracted at more negativity
membrane potential is the
electrical driving force
explain what you are looking at with nernst equation
if you have given chemical concentrations, are going to calculate the other driving force (electrical) and be equal opposite
Vm =?
membrane potential (electrical)
log of 100 is
2
log of 10 is
1
log of 1000 is
3
. for any univalent ion if there is tenfold difference need what to oppose it
60 mV
look at and understand pg 15
pg 15
look at and understand pg 16
16
hyperkaeilemia is what
outside of cell have higher potassium
increase in extracellular potassium
why does potassium have bigger impact on membrane potential than sodium
Leak channels. Theres more leak potassium channels present so theres more movement of potassium and it has more of an impact on membrane potential.
10 fold difference in univalent ion needs what as the other driving force
60 mV as other driving force
change in driving force of potassium is going to change by factor of
60
