Membrane Potentials and Action Potentials

Question 1

Electrochemical Equilibrium

Answer 1

Electrical forces balance diffusion forces. A stable transmembrane potential is achieved

Question 2

What equation can be used to calculate the equilibrium potential (E)?

Answer 2

Nerst Equation

Question 3

What is the Nerst Equation?

Answer 3

E = ((RT)/(zF)) ln([X2]/[X1])

Question 4

What are the variables in the Nerst equation?

Answer 4

R = gas constant
T = Temperature in °Kelvin
z = charge on ion (-1 for Cl-, +2 for Ca2+)
F = Faraday’s number - charge per mol of ion
ln = natural logarithm (log to base e)
X2 = intracellular ion concentration
X1 = extracellular ion concentration

Question 5

What does the GHK equation show?

Answer 5

The resting membrane potential (Em)

Question 6

Depolarisation

Answer 6

Membrane potential increases from negative towards 0

Question 7

Repolarisation

Answer 7

Membrane potential decreases towards resting potential

Question 8

Overshoot

Answer 8

Membrane potential becomes more positive than 0

Question 9

Hyperpolarisation

Answer 9

Membrane potential becomes more negative than resting potential

Question 10

Passive propagation

Answer 10

Only resting K+ channels open

Question 11

What are the three main factors that influence the movement of ions across the membrane?

Answer 11

Conc. of ion on both sides of the membrane.
Charge of the ion.
Voltage across the membrane.

Question 12

Why is the K+ equilibrium potential negative (e.g. -70mV) and the Na+ equilibrium potential positive(e.g. +40mV) when both are positive ions?

Answer 12

More K+ inside than out so flow is out of the cell, Na+ is opposite so flows into the cell. -70mV potential is needed to attract K+ and stop net outward flow. +40mV needed to repel Na+ entering cell.

Question 13

What factors influence the speed of propagation of an action potential along an axon?

Answer 13

Larger axons have lower resistance.