Membrane Potential

Question 1

Electrical Current

Answer 1

flow of electric charge

Question 2

Ions

Answer 2

Carrier of current in an electrolyte

Question 3

Voltage

Answer 3

the electrical force between two points that would drive an electric current between those
points

Question 4

Ion movement is

Answer 4

the basis of neuronal excitability

Question 5

Ions involved in neuronal excitablity:

Answer 5

• Sodium Na+
• Potassium K+
• Chloride Cl-

Question 6

Concentration gradients of ions

Answer 6

create electrical potentials

Question 7

Ion transporters

Answer 7

• Actively move ions against concentration gradient
• Create ion concentration gradients

Question 8

Ion channels

Answer 8

• Allow ions to diffuse down concentration gradient
• cause selective permeability to certain ions

Question 9

Membrane proteins regulate

Answer 9

flux of ions in and out of the cell

Question 10

Ion distribution sets up

Answer 10

a potential across the membrane

Question 11

Flux of ions across the membrane is determined by

Answer 11

a
concentration gradient, an electrical driving force, and

Question 12

Nernst Equasion

Answer 12

Used for uncovering the reversal or equilibrium potential of a single ion

Question 13

Reversal or equilibrium potential

Answer 13

The movement of any ion stops when the electrical force repelling [ion] equals the force of the concentration gradient

initially, K+
ions will flow along their concentration gradient
out of the cell.

this builds up an excess of positive charge on the outside
→ potential difference → this impedes further efflux of K+
, so that eventually an equilibrium is reached → this is EK

Question 14

Resting Vm (Potential) depends primarily on

Answer 14

K+ concentration gradient

(Hodgkin and Katz, 1949)

Question 15

membrane potential depends on

Answer 15

the concentration gradient,
the electrical driving force, and the relative permeability of the
membrane for a given ion

Question 16

many channels open

Answer 16

high conductance

Question 17

many channels closed

Answer 17

high resistance

Question 18

Thus the membrane potential will not be right at EK, but

Answer 18

slightly
depolarized from EK by an amount of approximately 5% of the
140 mV difference between EK and ENa.

Question 19

conductance (g)

Answer 19

a measure of the permeability of an ion

Question 20

Contribution of various ions to the resting potential depends on

Answer 20

their
equilibrium potential and their conductance

Question 21

At the resting potential the membrane permeability largely reflects

Answer 21

constituently
open (“leak”) potassium and chloride channels.

Question 22

Goldman equation (Goldman-Hodgkin-Katz equation)

Answer 22

Describes equilibrium in an environment with more than one ion

Question 23

For any given ion its distribution across the membrane is determined by

Answer 23

1. The chemical gradient
2. The electrical gradient
3. Permeability (conductance)

Question 24

Maintaining concentration gradients and thus the resting membrane
potential is

Answer 24

an active process (i.e. requires energy)

Question 25

Cells maintain gradients actively
with the

Answer 25

Na+
/K+ ATPase
(sodium-potassium pump)
or other ion co-transporters

Question 26

The resting membrane
potential is ___ an equilibrium
potential

Answer 26

NOT.
it relies on the
constant expenditure of
energy (e.g. ATP) by ion
pumps for its maintenance.

Question 27

Membrane potential can be changed by

Answer 27

altering ion gradients
(i.e. via pumps) or permeability

Question 28

Cells vary permeability of membrane by

Answer 28

opening/closing
channels (→ changes in conductance).