Resting Membrane Potential

Question 1

What is membrane potential?

Answer 1

The magnitude of an electrical charge existing across a plasma membrane

Question 2

How is membrane potential always expressed?

Answer 2

The potential inside the cell relative to the extracellular solution (measured in mV)

Question 3

Which cells have the largest resting membrane potentials?

Answer 3

Cardiac and skeletal muscle cells:

-80 to -95 mV

Question 4

Which cells have the smallest resting membrane potential?

Answer 4

Erthyrocytes:

-9mV

Question 5

What is the resting membrane potentials of nerve cells?

Answer 5

-50 to -75 mV

Question 6

How can membrane potential be measured?

Answer 6

Voltmeter used
The microelectrode is a fine flass pipette - tip diameter is less than 1 micrometre
This can penetrate cell membrane without bursting cell
Filled with a conducting solution (KCl)

Question 7

What are the two factors important for the generatio of membrane potential?

Answer 7

Ion concentration gradients and selective ion channels

Question 8

What are the most important ion channels for most cells?

Answer 8

K+, Na+ and Cl-

Question 9

What are ion channels?

Answer 9

Proteins that enable ions to cross cell membrane

Question 10

What is the phospholipid bilayer permeable to?

Answer 10

Small uncharged molecules - oxygen, carbon dioxide, water, benzene

Question 11

What is the phospholipid bilayer very impermeable to?

Answer 11

Charged molecules (ions

Question 12

What will chloride channels also move?

Answer 12

Other halide ions

Question 13

What are some properties of ion channels?

Answer 13

Selectivity for one or few ion species, pore opens/closes by conformational change and rapid ion flow down the electrochemical gradient

Question 14

Are there more proteins inside or outside of the cell?

Answer 14

More proteins intracellularly which makes the inside of the cell more negatively charged

Question 15

What are the intracellular and extracellular levels of K+?

Answer 15

Intracellular = 160 mM
Extracellular = 4.5 mM

Question 16

What are the intracellular and extracellular levels of Na+?

Answer 16

Intracellular = 10 mM
Extracellular = 145 mM

Question 17

What are the intracellular and extracellular levels of Cl-?

Answer 17

Intracellular = 3 mM
Extracellular = 114 mM

Question 18

What dominates the membrane ionic permeability at rest?

Answer 18

Open K+ channels

Question 19

How does the resting membrane potential arise?

Answer 19

Because the membrane is selectively permeable to K+

Question 20

What does the Nerst equation allow you to calculate?

Answer 20

Membrane potential at which K+ will be in equilibrium, given the extracellular and intracellular K+ concentrations

Question 21

True or False:

If a membrane is selectively permeable to K+ alone, its membrane potential will be at Ek.

Answer 21

True

Question 22

What is the Nerst equation?

Answer 22

Eion = 61/Z x log10 (ion out/ion in)

Question 23

What would happen to the membrane potential if there was an increase in the permeability of the membrane to K+ ions?

Answer 23

K+ ions would move out of the cell so there will be a more negative intracellular charge and a more positive extracellular charge

Question 24

Some neurotransmitters act to increase Cl- conductance in the postsynaptic cell. What are the consequences of this for the membrane potential?

Answer 24

An increase in Cl- inside the postsynaptic cell would make it more negative inside so it becomes a lot harder for the sodium ions to enter and depolarise the cell

Question 25

In a hyperkalaemic patient, the plasma K+ concentration was found to be 7.5 mM. Assuming a similar value for the interstitial fluid, what would the consequences be for the resting cell membrane?

Answer 25

Higher extracellular potassium
Potassium usually moves out of the cell but is less likely to do this
Inside of the cell is more positive
Easier to depolarise