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"Ionic Basis of Rest Mem Pot"
9/12/07--for quiz 1
5
Physiology
Not Applicable
09/12/2007

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Term
What is "equilibrium potential"?
Definition
--Diffusion potential that exactly opposes the tendency for diffusion down conc. gradient.

--Ex: Cation diffuses-->increases positive charge on other side of membrane-->stop further diffusion of cation.
Term
What is the Nerst equation?

What is its basic concept?
Definition
--Used to calculate the equilibrium potential for an ion at a given concentration difference across a membrane.

--Calculated 1 ion at a time!

E=-2.3 RT/Zf x Log (Ci)/(Ce)

E= equilibrium potential
2.3RT/F= constant (60 mV)
z= charge on the ion (+1, +2, -1..)
Ci= intracellular concentration
Ce= extracellular concentration
Term
What are approximate Nerst potentials for:
Na+, K+, Cl-, and Ca2+?
Definition
ENa+= +65 mV
EK+= -85 mV
ECl-= -90 mV
ECa2+= +120mV
Term
What is cord conductance equation?
Definition
--Evaluates contribution that EACH ion makes to membrane potential.
--Weights equilibrium potential (calculated by Nerst) for each ion by its conductance.

--Ions w/ HIGH conductance=drive membrane TOWARD equilibrium potential
--Ions w/LOW conductance=have little effect on membrane.
Term
What is Goldman-Hodgkin-Katz equation?
Definition
--Considers contribution of EACH ion to membrane potential by its relative permeability, rather than conductance (chord conductance)

Em=((gK+/gT)x (EK+))+((gNA+gT) x (ENa+))+ ((gCl-/gT) x (ECl-)) + ((gCa2+/gT) x (ECa2+))

Em= membrane potential
gK+...= K+ conductance; etc.
gT= total conductance
Ek+...=equilibrium potential
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