Module 3 Lecture 1

Question 1

What does the term membrane potential mean?

Answer 1

The difference in electrical potential inside and outside the cell

Allows for the potential of ion movement to occur across the membrane due to charge-charge attractions and repulsions

Question 2

What is meant by potential when it comes to ion movement?

Answer 2

Separated charges across a membrane have the potential to create an effect on the membrane

Ions going either in or out the cell

Question 3

What are key factors regarding membrane potential?

Answer 3

• Separation of charge across a membrane
• Difference in relative concentrations of Cations and Anions in the ICF and ECF
• Permeability is different in key ions
• Ion movement (therefore, membrane potential) is influenced by ion concentration and membrane permeability
• Membrane potential measured as Volt or Milivolt

Question 4

What determines the movement of ions across a membrane?

Answer 4

• Concentration gradient
• Electrical gradient
• Membrane permeability

Electrochemical gradient = combined effects of both concentration and electrical

Question 5

What is resting membrane potential?

Answer 5

All cells (both excitable and non-excitable) have a constant membrane potential at rest
* Commonly known for being at -70mV

Excitable would be constant if it is not producing electrical signals

Question 6

Is the membrane itself charged?

Answer 6

No; it’s a thin layer surrounding the membrane that holds the relative charge

The thin layer is not the ECF or ICF as they are neutral; it is a layer that surrounds the surface of the cell membrane

Question 7

What does the magnitude of the potential depend on?

Answer 7

The difference in separated charge.

If the difference in charge on one side is significantly bigger than the other side => greater membrane potential

Question 8

What are excitable cells?

Answer 8

Includes nerve & muscle cells
* Produce rapid and transient changes in resting membrane potential when excited

The changes in potential for the membrane serve to create electrical signals to pass down (communication purposes)
Both non-excitable and excitable have resting membrane potential

Question 9

What key ions contribute to the membrane potential?

Answer 9

1. K+
2. Na+
3. A-

A- is a large intracellular protein that cannot cross the membrane

Question 10

What is relative permeability?

Answer 10

How permeable a membrane is for an ion

Potassium has the most influence on resting membrane potential because it is the most permeable ion because there are more passive K+ channels (leak channels) that are open to K+ rather than Na+

Question 11

If a cell was only permeable to K+ what would happen?

Answer 11

• Initially the K+ would go down its concentration gradient (outside the cell)
• There would be too much K+ outside the cell that it would reverse the electrical gradient and move back in a little
• Dynamic equilibrium will be reached when there is equal charge on both sides of K+ ions

Membrane potential at this point is called potassium equilibrium potential - large K+ concentration gradient exists but no net movement
- Potassium Equilibrium Potential (Ek) = -90mV

Question 12

Why is the Equilibrium Potential of Potassium (Ek) a negative number?

Answer 12

You measure it with respect to the inside of the cell

Since positive ions are leaving the cell, the inside becomes more negative

Question 13

What if a cell was only permeable to Na+

Answer 13

• Concentration & electrical gradient pushes Na+ into the cell
• Inside of the cell becomes more +ve and eventually it will want to equilibrate with the Na+ outside the cell
• No more net movement of Na+ occurs

Membrane potential in this case is called Sodium Equilibrium Potential (+65 mV)