Resting Cell Membrane

Question 1

What is a membrane potential?

Answer 1

All cells have an electrical potential difference across their plasma membrane. It is the electrical charge that exists across a membrane.

Question 2

Give an example of why the membrane potential is important.

Answer 2

Provides the basis of signalling in the nervous system as well as in many other types of cells.

Question 3

How is membrane potential expressed? (Not units, but which environment is being measured in contrast to which)

Answer 3

As the potential inside the cell relative to the extracellular solution.

Question 4

What charge is the resting membrane potential?

Answer 4

Always negative.

Question 5

Outline how membrane potential is measured.

Answer 5

Using a microelectrode which is a fine glass pipette with a tip diameter of less than a micrometer which penetrates the cell membrane. The microelectrode is filled with a conducting solution (KCl). This gives the voltage meter a charge.

Question 6

Give three examples of which membrane potentials that can be measured.

Answer 6

1: A cell’s plasma membrane
2: The inner mitochondrial membrane
3: The endoplasmic reticulum membrane

Question 7

What unit is the membrane potential measured in?

Answer 7

Millivolts (mV)

Question 8

What is the range of resting membrane potentials in eukaryotic cells?

Answer 8

-20 mV to -90 mV

Question 9

Which type of cells have the largest resting membrane potentials?

Answer 9

Cardiac and skeletal muscle cells.

Question 10

What is the range of resting membrane potential in nerve cells?

Answer 10

-50 mV to -75 mV

Question 11

What is the resting membrane potential in cardiac myocytes?

Answer 11

-80 mV

Question 12

What is the resting membrane potential in skeletal muscle myocytes?

Answer 12

-90 mV

Question 13

What is the resting membrane potential in smooth muscle myocytes?

Answer 13

-50 mV

Question 14

Why are the absolute numbers of the concentration of ions outside of the cell (extracellularly) more important than the concentration of ions intracellularly?

Answer 14

Because the extracellular values which are usually in the plasma of the blood is where we do electrolytic measures in forms of taking blood of patients.

Question 15

At resting potential, what is the concentration of sodium ions intracellularly contra its concentration extracellularly?

Answer 15

12 mM intra
145 mM extra
intra < extra

Question 16

At resting potential, what is the concentration of potassium ions intracellularly contra its concentration extracellularly?

Answer 16

155 mM intra
4.5 mM extra
intra > extra

Question 17

At resting potential, what is the concentration of chloride ions intracellularly contra its concentration extracellularly?

Answer 17

4.2 mM intra
123 mM extra
intra < extra

Question 18

At resting potential, what is the concentration of anions other than chloride ions intracellularly contra its concentration extracellularly?

Answer 18

167 mM intra
40 mM extra
intra > extra

Question 19

At resting potential, what is the concentration of calcium ions in the cytoplasm contra its concentration extracellularly?

Answer 19

less than 0.0001 mM intra
1 mM extra
intra < extra
about 10000x higher extra!

Question 20

How are the gradients for potassium and sodium ions set up?

Answer 20

By the Na+/K+ ATPase

Question 21

For most cells, what is the membrane potential dominated by?

Answer 21

The action of potassium ion channels.

Question 22

Are the potassium ion channels open or closed at rest?

Answer 22

Open.

Question 23

Outline how the resting potential is set up.

Answer 23

K+ channels are open and K+ leave the cell down the chemical gradient. Anions are left behind and therefore the potential on the inside which is already negative becomes increasingly negative. This sets up an electrical gradient for K+ into the cell.

Question 24

What happens when the chemical gradient and the electrical gradient is equal?

Answer 24

There is no net movement of K+, but there will still be a negative membrane potential.

Question 25

What is the equilibrium potential?

Answer 25

When the chemical gradient and electrical gradient of an ion is equal and therefore at equilibrium. There is no net movement of the ion across the membrane.

Question 26

How is the equilibrium potential of an ion calculated?

Answer 26

With Nernst equation

Question 27

What is the equilibrium potential of potassium ions?

Answer 27

-95 mV

Question 28

Explain why the resting membrane potential of cells does not equate the equilibrium potential of potassium ions.

Answer 28

Because the plasma membrane of a cell is not perfectly selectively permeable to potassium. It also allows some influx of sodium and calcium. There is a little bit of a ‘leak’ as the sodium and calcium channels can ‘flicker’.

Question 29

Explain why the resting potential of smooth muscle cell is so much higher than the equilibrium potential of potassium.

Answer 29

Because there is an increased contribution of other ions. Other ions have an increased permeability to get transported into the membrane, or out depending on their charge.