Physiology Membrane Lecture 3 - The Resting Membrane Potential

Question 1

All plasma membranes of cells are polarised electrically which is know as membrane potential. What is membrane potential?

Answer 1

It is the separation of opposite charges across the membrane.

The difference in charge across a membrane (refers to the difference in charge between the thin layers of ECF and ICF located next to the inside and outside of the membrane, respectively)

The unequal distribution of ions and their selective movements through the plasma membrane.

Question 2

What is Em?

Answer 2

Membrane potential

Question 3

Is the plasma membrane charged?

Answer 3

Not charged

Question 4

What are the units of membrane potential?

Answer 4

mV

Question 5

What cells can produce a rapid, transient changes in their membrane potentials when excited (action potentials)?

Answer 5

Excitable cells e.g. nerve and muscle cells

Question 6

What is meant by resting membrane potential?

Answer 6

This is the constant membrane potential in non-excitable cells and the membrane potential of excitable cells at rest.

Question 7

What is the concentration gradient for K+ and Na+ directionally specking?

Answer 7

K+ is outward

Na+ is inward

Question 8

K+ and Na+ are cations (positively charged). What is their electrical gradient towards?

Answer 8

Their electrical gradient is always towards the negatively charged side of the membrane!

Question 9

Where is the concentration of Na+ and CL- highest?

Answer 9

In the extracellular fluid

Question 10

Where is the concentration of K+ highest>

Answer 10

In the intracellular fluid because their are more leak channels for K+ than Na+. At resting potential the membrane is 100x more permeable to K+ than Na+

Question 11

Why is the membrane 100x more permeable to K+ than Na+?

Answer 11

There are more leak channels for K+

Question 12

What is meant by Ek or K+ equilibrium?

Answer 12

It is the equilibrium potential. The membrane of the cell initially has no charge. K+ will move down its concentration gradient to the outside of the cell leaving behind a negative charge. However, K+ will be attracted back into the negatively charged cell as it is positively charged. This tug of war will continue until the forces are balance. This is when the equilibrium is reached!

Question 13

What are the two apposing forces acting on K+ in terms of plasma membrane?

Answer 13

1. The concentration gradient (moving K+ out go the cell)

2. The electrical gradient (tending to move K+ into the cell)

Question 14

When does no further net movement of K+ occur in terms of Plasma membrane?

Answer 14

No net movement is reached at equilibrium when the forces are balanced! (concentration gradient vs. electrical gradient)

Question 15

What is the membrane potential for Ek?

Answer 15

-90mV

Question 16

What is the Nernst equation?

Answer 16

It is the calculation of equilibrium potential for any given ion.

Question 17

What is meant by ENa or Na+ equilibrium?

Answer 17

It is the equilibrium potential for Na+. At the beginning there is no membrane potential. There are more Na+ ions outside the cells so there is an inward movement of Na which causes a build up of positive charges inside the cell and leaves negative ions (mostly Cl-) outside the cell.

Question 18

What can a greater permeability for a given ion do in terms of equilibrium potential?

Answer 18

The greater the permeability for a given ion, the greater the tendency for that ion to drive membrane potential towards the ion’s own equilibrium potential.

Question 19

Are all cells negative or positive inside?

Answer 19

Negative

Question 20

Why does membrane potential vary for different cell types?

Answer 20

Different cells have different permeability (for Na+ and K+ due to different number of leak channels)

Question 21

What is the equilibrium potential (Em) for the membrane?

Answer 21

It is the potential for a membrane considering all other ions e.g Na+ and K+

Question 22

What is Goldman-Hodgkin-Katz equation?

Answer 22

It is the equation used to calculate equilibrium potential considering all the ions.

Question 23

What helps maintain the K+ and N+ gradients across the membrane?

Answer 23

Na+K+ pumps

Question 24

What does hyperpolarizing mean?

Answer 24

The change in membrane potential making it more negative.

Question 25

Why do Na+K+ pumps have a hyperpolarizing affect?

Answer 25

As every 3Na+ are exported, 2K+ are imported

Question 26

Why does the amount of current change the Na+K+ pump add vary?

Answer 26

Different cell types have different pump activity and resistance of the membrane

Question 27

What is the typical equilibrium potential for a resting cell?

Answer 27

Between -60mV and -85mV

Question 28

What is the specialised use of Em in nerve and muscle cells?

Answer 28

Rapidly and transiently alter their membrane permeabilities in response to appropriate stimulation, resulting in fluctuations in Em.

Nerve impulses in nerve cells and triggering contraction in muscle cells - Changes in Em linked to secretion of insulin from pancreatic Beta-cells.

Question 29

What accounts for the magnitude of the resting membrane potential?

Answer 29

The magnitude of K+ and Na+ concentration gradients, together with differences in permeability of the membrane to these ions.

Question 30

At rest which is Em closer to, Ek or ENa?

Answer 30

Ek