M&R Session 3 - Resting Cell Membrane

Question 1

Give a range of normal values for resting membrane potential (all cells)

Answer 1

Between -20mV and 90mV

Question 2

Give a range of normal values of resting membrane potential for skeletal muscle cells.

Answer 2

Between -80mV and -90mV

Question 3

Give a range of normal values of resting membrane potential for nerve cells.

Answer 3

Between -50mV and -75mV

Question 4

What quality of the plasma membrane allows the membrane potential to be set up?

Answer 4

Selective permeability

Question 5

What 3 characteristics see seen in ion channels involved in membrane potential?

Answer 5

• Selectivity (for one or two ions)
• Gating (pore can open or close)
• Rapid ion flow (ions flow down electrochemical gradient)

Question 6

Explain the setting up of the membrane potential by K+ channels.

Answer 6

1. K channels are open at rest.
2. As such, K+ will flow down its concentration gradient, out of the cell.
3. However, as anions are unable to pass through the plasma membrane, there is an overall negative charge inside the membrane.
4. This negative charge inside the membrane resists further K+ migration out of the cell, and equilibrium is set up.

Question 7

What is equilibrium potential?

Answer 7

The membrane potential at which there is no net movement in or out of the cell. Calculated using the Nernst Equation.

Question 8

What is the altered version of the Nernst equation used in practice due to human constants?

Answer 8

Ey = 61mV x {log ([y]e/[y]i)

Where mV is units for membrane potential (millivolts)
Y is ion being measured.

Question 9

What is the approximate value of E(k)? (The equilibrium potential for potassium)

Answer 9

-95mV

Question 10

Why is the resting membrane potential of neurones close to, but not exactly, the equilibrium potential for K?

Answer 10

The K+ channels dominate the resting permeability of most cells, including neurones, but in all living cells channels for Na and Ca “flicker open” and other ions leak into the cell, making the potential less negative.

In other words, the membrane is not perfectly selective for K.

Question 11

What two main changes are possible to resting membrane potential?

Answer 11

1. Depolarisation - Decrease in size of potential. Interior becomes less negative (eg -70mV –> -50mV)
2. Hyperpolarisation - Increase in size of potential. Interior becomes more negative (eg -70mV –> -90mV)

Question 12

What causes changes to membrane potential and why?

Answer 12

Changes in membrane potential come about from changes to permeability of ion channels to their corresponding ions.

If permeability is increased, the membrane potential shifts in the direction of that ion’s equilibrium potential.

Eg. Opening Na+ channels depolarises membrane.

These changes may be brought about by ligand, voltage or mechanical changes.

Question 13

What is membrane potential?

Answer 13

Membrane potential is the difference in electrical potential across a plasma membrane of a cell. It is always measured as the intracellular voltage relative to the extracellular voltage.

Question 14

What are the two types of synaptic transmission and what defines them?

Answer 14

Fast synaptic transmission - receptor is also a ligand-gated ion channel

Slow synaptic transmission - receptor uses G-protein.

Question 15

Which two neurotransmitters can stimulate an Excitatory post-synaptic potential (EPSP)?

Answer 15

Glutamate

Acetylcholine

Question 16

Which two neurotransmitters can stimulate an Inhibitory post-synaptic potential?

Answer 16

Glycine

GABA