Lecture 1 : Membrane Potential

Question 1

Learning Objectives :

Answer 1

• How ionic concentration gradients are maintained across plasma membrane via ion channels and protein pumps
• What the electrochemical gradient is
• What equilibrium potential is
• How resting membrane potential is achieved
• Impact of extracellular ion concentration changes

Question 2

What is the Vm of resting membrane potential

Answer 2

Vm = - 70 mV

(Vm = voltage across membrane at any moment)

Question 3

Ions which are present in nerve cells

Answer 3

• Na+
• K+
• Cl-
• Ca2+

Question 4

What are the concentrations of the 4 main ions inside and outside of a nerve cell?

Answer 4

Na+
15mM inside, 150mM outside

K+
100mM inside, 5mM outside

Cl-
13mM inside, 150mM outside

Ca2+
0.0002mM inside, 2mM outside

Question 5

Say K+ ion channels opened, what would happen across the membrane of a neurone

Answer 5

There is a higher concentration of K+ inside the cell than outside, so when K+ ion channels open, an efflux of K+ ions out of the cell occurs. This creates a negative charge in the IFC which draws K+ ions back into cell from the ECF. Electrochemical equilibrium is restored.

Question 6

What factors determine the electrical potential difference established across a membrane?

Answer 6

• Ion concentrations
• Selective ion movement across a membrane
• Membrane permeability

Question 7

What is the Nernst equation?

Answer 7

Question 8

What is the equilibrium potential (Eion)? What are they for different ions?

Answer 8

Eion is the membrane potential that would be achieved if the membrane was selectively permeable to that ion.

Question 9

Something to note about how this works

Answer 9

Ek is around -80mV
Ena is around +60mV

But Vm at resting potential is -70mV, so the membrane cannot be permeable to only 1 ion

Question 10

Goldmann equation

Answer 10

Question 11

Differential permeability

Answer 11

Differential permeability is the ability of a cell membrane to allow only certain particles to pass through

Question 12

What is hypokalemia and hyperkalemia

Answer 12

Hypokalemia - Reduced [K+] outside cell, more [K+] efflux, Vm more negative

Hyperkalemia - Increased [K+] outside of cell, less drive to reach Ek, Vm more positive

Question 13

Why is this all important?

Answer 13

• Homeostasis
• Generating action potentials in neurones
• Muscle contractility