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resting potential will be closest to potassium.
-how do you figure this out? through goldman-hodgkin-katz equation,
calculate membrane potential of cell with permeability to all 3.
-if 2 contribute equally, membrane potential will be in between them,
-membrane potential approach equilibrium potential of whatever
contribue most EK Goldman-Hodgkin-Katz Equation: Vm=61 log PK [K+]out + PNa [Na+]out + PCl [Cl-]in
mV PK [K+]in + PNa [Na+]in + PCl [Cl-]out Something to Remember
***IMPORTANT (VERY VERY VERY)***:
-so sodium increase, Vm approach that. If the permeability for
a particular ion
will change, tending to
move toward the
for that ion. Ion Leakage and Na+/K+ Pumps
5 mM OUT Na/K
pump 145 mM
15 mM IN Na+ ENa = +60 mV 2 K+ EK = -90 mV ATP inner ear is exception: sodium and chlroide always inward except in inner
tricky: potassium may not be always outward. but there's a problem in that
channels are leaking all the time.
arc=nerve cell at rest, above is
extracellular fluid. membrane is
more permeable to potassium in
that more potassium channels are
open than sodium channel at rest.
membrane potential is going to be
in between the equilibrium
potential of sodium and potassium
(~ -70mV). here's the problem: the
equlibrium potential for potassium
at -90 means that outwardly
directed concentration -driven flux
of potassium is equal inwardly
directed electrically-driven flux
only at -90. at other potential, -70,
this is not true. the membrane is
20 mV out of equilibrium, so
outward concentration-driven flux
do not equal and oppositive of
inward electrical driven flux. in
fact, the outwardly concentration
flux is greater than inward
electrical-driven flux. so there's a
net outward movement for
potassium. under these condition
means theres a constant leak of
potassium out of cell, which is bad
b/c sodium-potassium pump burn
a lot of ATP to stuff cell with
potassium which are leaking out.
what's worse is that some sodium
channels, although not as ma...
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- Spring '09