Membrane Potential Generation

Question 1

Define resting ion channels.

Answer 1

Always open K+ channels, generate RMP, ‘leaky’ channels

Question 2

Define gated channels.

Answer 2

Closed when membrane is at rest, regulated by changes in membrane potential, ligand binding or stretch

Question 3

What generates an electrical potential?

Answer 3

Differences in specific concentrations of specific ions
Membranes are selectively permeable
Presence of active transporters
Specific types of ion channel

Question 4

What type of ion lines the outer membrane?

Answer 4

Cloud of positive ions

Question 5

What type of ion lines the inner membrane?

Answer 5

Thin cloud of negative ions

Question 6

What calculation is used to define the membrane potential?

Answer 6

Vm = Vin - Vout
Vout is defined as zero

Question 7

What are positive and negative ions called?

Answer 7

Cations (+ve)
Anions (-ve)

Question 8

Define direction of current flow?

Answer 8

Direction of net movement of positive ions

Question 9

What does a reduction of charge cause?

Answer 9

Depolarisation of the membrane - less negative

Question 10

What does an increase of charge cause?

Answer 10

Hyperpolarization of the membrane potential - more negative

Question 11

Define equilibrium potential?

Answer 11

The balance of electrical driving force and chemical driving force

Question 12

What ions are found mostly extracellularly?

Answer 12

Sodium and Chloride

Question 13

What ions are found mostly intracellularly?

Answer 13

Potassium

Question 14

Define a membrane potential at rest.

Answer 14

Potential at which the flow of ions out (mostly K+) is equal to the flow of ions in (mostly Na+)

Question 15

What maintains the membrane potential at rest?

Answer 15

Pumps eg. Na/KATPase

Question 16

What creates a charge imbalance?

Answer 16

Ions moving down their electrical gradient which acts in opposition to the concentration gradient.

Question 17

When is equilibrium potential achieved?

Answer 17

When the concentration forces are balanced by these electrical forces.

Question 18

Why is RMP usually ~ -70mV?

Answer 18

Due to the high permeability of the membrane to K+ and small relative permeability of membrane to Na+

Question 19

Define the Nernst Equation.

Answer 19

Ek = (RT/zF)ln([K+]0/[K+]i) = 58mV

Question 20

Why do we use the Goldman Hodgkin-Katz equation?

Answer 20

In order to calculate the RMP, the permeabilities and concentrations of Na+, K+ and CL- must be considered

Question 21

What does the equilibrium of the cell depend on when 7 ions are present?

Answer 21

The relative permeability of the ions
AT rest the permeabilities have the ratio PK:PNa:PCl = 1:0.03:0.1

Question 22

What ratio is the RMP close to and why?

Answer 22

K equilibrium potential as PK dominates

Question 23

What happens to the membrane potential during an action potential?

Answer 23

Membrane potential depolarises towards equilibrium potential for Na+ ions

Question 24

What are the differences between membrane potential and equilibrium potential?

Answer 24

Vm is a steady state and represents a synthesis of all these forces but it is not equilibrium.
Eq is an equilibrium potential