Term
| What is "equilibrium potential"? |
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Definition
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--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.
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Term
| What is the Nerst equation?
What is its basic concept? |
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Definition
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--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
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Term
| What are approximate Nerst potentials for:
Na+, K+, Cl-, and Ca2+? |
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Definition
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ENa+= +65 mV
EK+= -85 mV
ECl-= -90 mV
ECa2+= +120mV
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Term
| What is cord conductance equation? |
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Definition
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--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.
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Term
| What is Goldman-Hodgkin-Katz equation? |
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Definition
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--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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