Session 4: Resting Membrane Potential

Question 1

What is a membrane potential?

Answer 1

The electrical potential difference across the plasma membrane of ALL cells

Question 2

How is the resting potential of a cell measured?

Answer 2

Using a very fine glass micropipette called a microelectrode to penetrate the cell membrane
The micropipette is filled with conducting solution

Question 3

What are the range of values for resting potentials of animal cells?

Answer 3

-20mV to -90mV

Question 4

The resting membrane potentials are largest in which cells?

Answer 4

Skeletal muscle and cardiac muscle (-80mV to -95mV)

Question 5

What is the range of nerve cell resting potential?

Answer 5

-50mV to -75mV

Question 6

Explain the concept of selective permeability

Answer 6

The resting membrane can be selectively permeable to ions, based on the types of ion channel proteins that are in the membrane and whether gated channels are open or not

Question 7

How does selective permeability of cell membranes arise?

Answer 7

Through channel proteins present in the cell membrane which allow some ions to permeate. They are characterised by selectivity, gating and a high rate of ion flow down the electrochemical gradient for the ion

Question 8

How is the resting potential set up given the distribution of ions across cell membrane?

Answer 8

At rest, the a typical mammalian cell has open K+ channels, so is selectively permeable to K+. Since anions cannot follow, the cell becomes negatively charged inside with the generation of an electrical gradient

Question 9

What is the “equilibrium potential for an ion”?

Answer 9

The electrical and chemical gradients for K+ are equal and balance so there is no net driving force on K+ across the membrane

Question 10

How would you calculate equilibrium potential for an ion from the ionic concentrations on either side of the plasma membrane?

Answer 10

Using the Nernst equation

Question 11

What is depolarization?

What happens to the interior of the cell in relation to charge?

Answer 11

A decrease in the membrane potential, so that the inside of the cell becomes less negative

Question 12

What is hyperpolarisation?

What happens to the interior of the cell in relation to charge?

Answer 12

An increase in the membrane potential, so that that the inside of the cell becomes more positive

Question 13

Explain mechanisms that may lead to depolarisation

Answer 13

Opening Na+ or Ca2+ channels

Question 14

Explain the mechanisms hat may lead to hyperpolarisation

Answer 14

Opening K+ or Cl- channels

Question 15

Explain how changes in ion activity can lead to changes in the membrane potential

Answer 15

c

Question 16

Outline some of the roles of the membrane potential in signalling within and between cells

Answer 16

c

Question 17

Outline how ligand-gated channels can give rise to synaptic potentials

Answer 17

Synaptic potentials can be fast or slow depending on wether the receptor is also an ion channel, and depending on which ions the channels are selective for

Question 18

What does increasing the membrane permeability for a particular ion do to the membrane potential for that ion?

Answer 18

Moves it towards the equilibrium potential

Question 19

How do we deal with real membranes that are not perfectly selective for one ion species?

Answer 19

Use the Goldman-Hodgkin-Katz (GHK) equation

Question 20

How do we deal with real membranes that are not perfectly selective for one ion species?

Answer 20

Use the Goldman-Hodgkin-Katz (GHK) equation

Question 21

In fast synaptic transmission, the receptor is also what kind of channel?
What does this mean?

Answer 21

Ligand-gated ion channel
It has two functions:
1) It binds its related ligand (neurotransmitter)
2) It acts as an ion channel

Question 22

Depolarising transmitters open channels with _______ reversal potentials, i.e. channels selective for what?

Answer 22

Na+, Ca2+

Question 23

Do depolarising transmitters lead to excitatory or inhibitor postsynaptic potential?

Answer 23

Excitatory postsynaptic potential (EPSP)

Question 24

Hyperpolarizing transmitters open channels with _______ reversal potentials i.e. channels selective for what?

Answer 24

K+ or Cl-

Question 25

Do hyperpolarizing transmitters lead to excitatory or inhibitory postsynaptic potential?

Answer 25

Inhibitory postsynaptic potential (IPSP)

Question 26

What is the difference between fast and slow synaptic transmission?

Answer 26

In fast synaptic transmission, the receptor itself is a ligand-gated ion channel whereas in slow synaptic transmission it is not itself an ion channel, but signals to the channel

Question 27

Which two ways can the receptor in slow synaptic transmission signal to the channel?

Answer 27

Within the membrane -localised and rapid

Via an intracellular messenger - throughout the cell, amplified by cascade

Question 28

What two other factors can influence membrane potential, apart from ion channels?

Answer 28

Changes in ion concentration 
Electrogenic pumps (e.g.NA/K ATPase)