4.1 Resting Membrane Potential

Question 1

Define the membrane potential?

Answer 1

1. Magnitude of electrical charge that exists across a plasma membrane
2. Always expressed as potential INSIDE cell relative to EXTRACELLULAR solution
3. Measured in mV

Question 2

How can you measure a membrane potential?

Answer 2

1. Microelectrode (a fine glass pipettes <1um like a needle)
2. Filled with conducting solution (KCl)
3. Voltmeter reading - mV

Question 3

What 2 factors are required for a membrane potential established?

Answer 3

1. Asymmetric distribution of ions across plasma membrane

2. Selective ion channels in plasma membrane (K+, Na+, Cl-)

Question 4

What is the phospholipid bilayer permeable and impermeable to?

Answer 4

Permeable to small uncharged molecules

Impermeable to charged molecules

Question 5

What are ion channels ?

Answer 5

1. Proteins that enable ions to cross the cell membranes

2. Have an Aq pore which ions flow through by diffusion

Question 6

What three types of ion channels can you have?

Answer 6

1. Selectivity for one/few ion species
2. Gating - pore opening/closing by a conformational change in the protein
3. Rapid ion flow - always down electrochemical gradient

Question 7

Describe the electrical vs chemical gradient for K+.

Answer 7

Chemical gradient for K+ wants K+ OUT of the cell as lots inside

Electrical gradient for K+ wants K+ inside cell as its negatively charged (so want more positive ions inside)

Question 8

How is the resting membrane potential generated?

Answer 8

When chemical gradient force and electrical gradient force are equal and opposite for K+, no net movement of K+ but still negative charge across membrane

Question 9

What equation can be used to calculate the membrane potential for the ion concerned?

Answer 9

Nernst equation at 37degrees

E.g.
Ek+ = (61/z) log10 (K+(out))
K+(in)

Question 10

In a cell, where are concs higher for Na+, Ca2+, Cl-, K+, A-

Answer 10

Na+,Ca2+, Cl- higher outside

K+, A- higher inside

Question 11

What will increasing the permeability for a particular ion do to the equilibrium potential?

Answer 11

Move it closer to the equilibrium potential of that ion (Eion)

Question 12

What is the resting MP of cardiac muscle?

Answer 12

-90mV

Question 13

What is the resting MP of nerve cells?

Answer 13

-70mV

Question 14

Why do some cells have lower resting membrane potentials (e.g. -50mV for smooth muscle, RBC -9mV)

Answer 14

Less K+ channels and increased contribution from other channels

Question 15

What is the resting MP of skeletal muscle?

Answer 15

-90mV

Question 16

If the membrane was selectively permeable to one ion, where would the membrane potential be?

Answer 16

Equilibrium potential value from nernst

Question 17

If we had more Na+ or Ca2+ channels relative to K+ channels, what would be the resulting membrane potential and why?

Answer 17

Positive charge would be moving in so the membrane potential would be closer to 0

Question 18

If we had more K+ channels relative to Na+ or Ca2+, what would be the resulting membrane potential and why?

Answer 18

Potassium will move out leading to more negative membrane potential

Question 19

If we had more Cl- channels relative to K+ channels, what would be the resulting membrane potential and why?

Answer 19

Cl- moves into cell making inside more negative

Question 20

What dominates the resting membrane potential for most cells?

Answer 20

Open K+ channels