S6) The Resting Membrane Potential

Question 1

What is membrane potential?

Answer 1

• Membrane potential is the electrical potential difference across their plasma membrane of a cell
• It is expressed as a voltage of the inside of the cell relative to the outside

Question 2

How does one measure membrane potential?

Answer 2

A microelectrode (fine micropipette) penetrates the cell membranes and can be used to measure membrane potentials

Question 3

How are membrane potentials established?

Answer 3

Membrane potentials are established because the membrane is selectively permeable to different ions due to the presence/absence of channel proteins; membrane-spanning transport proteins that allow ions to permeate

Question 4

In terms of ion channels, differentiate between gating and selectivity

Answer 4

• Selectivity: the protein channel lets through only one/a few ion types

- Gating: the channel can be open/closed by a conformational change in the protein molecule

Question 5

Depending on which types of channels are open, the resting membrane can be selectively permeable to certain ion types.

Which ions are involved?

Answer 5

• Na⁺
• K⁺
• Cl^-
• Ca²⁺

Question 6

Outline the 6 steps involved in setting up the resting potential

Answer 6

⇒ Membrane is selectively permeable to K⁺ at rest (open K⁺ channel)

⇒ K⁺ diffuse out of the cell (down [K⁺] gradient)

⇒ Anions cannot follow

⇒ Cell interior becomes negatively charged

⇒ Newly-created membrane potential opposes outward movement of K⁺

⇒ System reaches equilibrium

Question 7

What is potassium equilibrium potential?

Answer 7

• Potassium equilibrium potential (E_k) is the membrane potential when the system reaches equilibrium and there is no net movement of K⁺
• This can be calculated from the Nernst equation

Question 8

Explain the relationship between E_k and resting membrane potential

Answer 8

• Open K⁺ channels dominate the resting permeability of many cells, so the resting membrane potential is close to the Ek
• The membrane is not perfectly selective so the RMP is less negative than Ek

Question 9

What is significant about the relationship between E_k and membrane potential?

Answer 9

The dependance of resting membrane potential on K⁺ permeability means that changing E_K with change the RMP