Week 3 ELM 6: The Nernst Equation

Flashcards covering key vocabulary and concepts from the lecture notes.

Nernst Equation

An equation that determines the equilibrium potential for a particular ion.

At rest, membrane is most permeable to __ ions.

Potassium

Capacitor

A device for storing energy via separation of electrical charge. Charge “stored” on two plates separated by an insulator

Automated External Defibrillator (AED)

Checks heart rhythm and can send electric shock to restore normal rhythm

Concentration of Na+ outside and inside the cell

150 mM outside, 15 mM inside. ratio 10:1

Concentration of K+ outside and inside the cell

5 mM outside , 100 mM inside . ratio 1:20

Concentration of Ca2+ outside and inside the cell

2 mM outside, .0002 inside. ratio 10000:1

Concentration of Cl- outside and inside the cell

150 mM outside and 13 mM inside. ratio 11.5:1

What is the charge of cell interior in respect to outside

-70-60 mV

In what direction do Na+ and Calcium move

In

Energy (work) formula due to electrical gradient

Work = z x F x V, where z is the charge, F is Faraday's constant (96500), and V is the potential difference. Energy it takes To move 1 mole of z-valent ions through a membrane potential of Vm Volts. Expressed in joules

1 Volt

is the potential difference required to move one coulomb of charge through an electric potential. If potential is 1 volt, it takes 1 joule of work to move 1 coulomb of charge.

Energy (work) formula due to concentration gradient

Work = R·T·ln (ci/co). R is the universal gas constant, T is the temperature in Kelvin, ci is the intracellular concentration, and co is the extracellular concentration. This formula measures energy required to move 1 mole of substance from a concentration ci (inside cell) to co (outside cell). Because ln 1 = 0, if ci = co, then no work is needed

Total work equation

Total work = z·F·V +R·T·ln(ci/co)

Three results of work and what they mean

Work > 0 = energy is needed to move ion across membrane, needs active transport

Work < 0 = energy is released when ion moves across membrane (“downhill” - occurs spontaneously)

Work = 0 = no energy required or released i.e. at equilibrium

Equilibrium case and how we derive Nernst equation

Total work = 0 = z·F·Vm +R·T·ln(ci/co)

z·F·V = - R·T·ln(ci/co)

V = ( R·T·ln(co/ci) ) / z x F