Resting And Changing Membrane Potential

Question 1

What is the membrane potential?

Answer 1

The magnitude of an electrical charge that exists across a plasma membrane. Potential inside relative to extracellular

Question 2

How is the membrane potential measured?

Answer 2

Using a microelectrode

It’s is a fine glass pipette with tip diameter <1um

Can penetrate the cell membrane

Filled with a conducting solution (KCl)

Question 3

What two factors are needed for the generation of the membrane potential?

Answer 3

Asymmetric distribution of ions across the plasma membrane

Selective ion channels in the PM

Question 4

What influences the membrane potential most at rest?

Answer 4

Open K channels dominate the membrane ionic permeability

Question 5

How do you calculate the equilibrium potential for an ion?

Answer 5

Nernst equation.

Ek = (61/z)log(IONo/IONi)

Question 6

Depolarisation is:

Answer 6

A decrease in the size of the membrane potential from its normal value. Cell interior becomes less negative

Question 7

Hyperpolarisation is:

Answer 7

An increase in the size of the membrane potential from its normal value. Cell interior more negative

Question 8

How does the membrane potential change because of ions?

Answer 8

Increasing membrane permeability to a particular ion moves the membrane potential towards the equilibrium potential for that ion.

Question 9

What causes hyperpolarisation?

Answer 9

Opening K or Cl channels

Question 10

What causes depolarisation?

Answer 10

Opening Na or Ca channels

Question 11

Define conductance:

Answer 11

The contribution of each ion to the membrane potential will depend on how permeable the membrane is to that ion.

Question 12

What are the types of gating on ion channels?

Answer 12

Ligand gating

Voltage gating - open or close in response to changes in membrane potential

Mechanical gating - open or close in response to membrane deformation

Question 13

What is the receptor in fast synaptic transmission?

Answer 13

Ion channel

Question 14

What do inhibitory transmitters do?

Answer 14

Open ligand gates ion channels permeable to K or Cl causing hyperpolarisation

Question 15

What is the mechanism for slow synaptic transmission?

Answer 15

The receptor and channel are separate proteins:

1) Direct G protein gating
2) Gating via an Intracellular messenger

Question 16

Two factors that can influence membrane potential:

Answer 16

Changes in ion concentration

Electrogenic pumps eg Na/K-ATPase

Question 17

What are the properties of cardiac ion channels?

Answer 17

Selectivity

Voltage sensitive gating

Time - dependence (some channels close a fraction of a second after they open - Fast Na channels)

Question 18

What is the resting potential in a cardiomyocyte ?

Answer 18

-90mV

Question 19

What is the threshold potential in cardiomyocytes?

Answer 19

-70mV

Question 20

Describe the action potential in cardiomyocytes:

Answer 20

• Na, Ca channels closed. Open K rectifier channels keep potential at -90
• Rapid Na influx through fast channels
• Transient K channels open and K Ed flux returns potential to 0
• Influx of Ca through L type Ca channels is balanced by K efflux through rectifier channels
• Ca channels close but delayed rectifier K channels remain open and return potential to -90