Origin of the membrane potential

Question 1

How is membrane potential generate?

Answer 1

Ion channels - mainly K+

K+ higher in cell than out

Question 2

When is equilibrium achieved

Answer 2

When the electrical gradient exactly balances the chemical gradient & there is no further net movement of ions

Question 3

What is the driving force?

Answer 3

the difference between the concentration and the electrical gradient?

Question 4

When is driving force zero?

Answer 4

Equilibrium

Question 5

What is Nernst equation for?

Answer 5

To predict when electrical vs chemical equilibrium will be achieved

Question 6

What do you need to know for Nernst equation?

Answer 6

relevant concentrations of the ions in question

Question 7

What is R, T, z, F in Nernst equation?

Answer 7

R = gas constant 8.31
T = Room temp
E = Vm
z = valency
F = faraday constant = 96480

Question 8

What is capacitance?

Answer 8

Cell membrane bilayer has charge holding capacity - capacitor

Question 9

Why is GHK equation better than Nernst?

Answer 9

Takes into account permeability ratio

Question 10

K+ conc, mV and permeability at rest (PX/PK)

Answer 10

Extracellular = 4
Intracellular = 120
mV = -90
PX/PK = 1.00

Question 11

Na+ conc, mV and permeability at rest (PX/PK)

Answer 11

Extracellular = 140
Intracellular = 10
mV = + 70
PX/PK = 0.04

Question 12

Ca2+ conc, mV and permeability at rest (PX/PK)

Answer 12

Extracellular = 2
Intracellular = 100 x 10-4
mV = +131
PX/PK = 0.20

Question 13

Cl- conc, mV and permeability at rest (PX/PK)

Answer 13

Extracellular = 100
Intracellular = 22
mV = -40
PX/PK = 0.11

Question 14

Stoichiometry of Na/K ATPase

Answer 14

3:2

3 Na ions moved out for 2 K ions moved in