Resting Membrane Potential

Question 1

Resting Membrane Potential (RMP) Definitions

Answer 1

Vm at steady state

§ No net ion flow and therefore no net current flow

Question 2

The lipid bilayer is equivalent to a ?
 Membrane proteins (ion channels) are equivalent to a

Answer 2

capacitor
conductance (inverse
resistance)

Question 3

Can approximate membrane capacitance to

Answer 3

1uF/cm^2

Question 4

o Cell membranes resemble ______ with a very high specific
capacitance (capacitance per unit membrane area). This reflects the small
_____- of the membrane bilayer (effectively 2.3nm)

Answer 4

parallel plate capacitors

thickness

Question 5

• Basis of Membrane Potential
  o Intra- and extracellular concentrations…..

Raising K+ causes

Answer 5

of sodium and potassium are different
o The membrane is also permeable to K+
o muscle contraction, but raising Na+ concentration has little
effect

Question 6

o => Bernstein hypothesises (1902)

Answer 6

that K+ gradient is responsible for resting

potential

Question 7

Nernst Equation

o A more quantitative expression…

Answer 7

for the equilibrium potential can be developed

if we consider the electrical and chemical energy of the ions in solution

Question 8

o The Gibbs Free Energy (G) of some ion is the sum

Answer 8

of the energy arising from

the chemical and electrical forces acting on the ion

Question 9

The tendency for ion ‘x’ to move L -> R depends on ?

§ The tendency for ion ‘x’ to move R -> L depends on?

Answer 9

G of ‘x’ on the L

G of ‘x’ on the R

Question 10

o When ΔG The Gibbs Free Energy of ion = 0, the forces are equal and opposite, i.e. is at equilibrium. The
potential difference is therefore:

Answer 10

0
0, the forces are equal and opposite, i.e. is at equilibrium.
This is the Nernst potential for an ion, i.e. the equilibrium potential for
a single ion.

Question 11

Nernst potential for an ion, § Also called the reversal potential, as

Answer 11

changing voltage to be above or

below the Nernst changes direction of current flow through membrane

Question 12

RMP almost entirely from

Answer 12

potassium due to high membrane

permeability to potassium

Question 13

• HH did experiments measurements

Answer 13

altering internal and external
concentrations of K+, found Nernst to be a good approximation
at high physiological [K+] but not at low

Question 14

GHK

Answer 14

At equilibrium, no net current flow:

Na +K+ Cl= 0

Question 15

GHK Similar development to Nernst, but uses ______ and _________
rather than concentration gradient and electrical gradient

Answer 15

diffusion and electrophoresis )(separation of charged particles

Question 16

GHK only applies when

Answer 16

Vm

is not changing

Question 17

GHK is a better approximation than Nerst when

Answer 17

Na+ permeability reduces slope below Nernst at low [K+]

Question 18

GHK equation meaning

Answer 18

Average of each ions concentration gradient, weighted by the ions
permeability

Question 19

GHK Allows membrane potential changes without :

Answer 19

bulk changes in ion level

Question 20

GHK Individual ion currents are:
Need NaK ATPase to keep ____ ______ _______
and prevent ‘run down’
• This means zero electrical current not strictly satisfied

Answer 20

non-zero

intracellular concentrations constant

Question 21

• Steady State Equation
  o GHK does not take into account the ____ -______ processes that maintain the
  intracellular sodium and potassium concentrations

Answer 21

ion transport

Question 22

GHK. Ongoing Na and K leaks are counteracted by the____

- Electrogenic (producing a change in the electrical potential of a cell.)

Answer 22

Na-K ATPase

Question 23

Chord Conductance Model _____analogue to GHK

Answer 23

Electrical

Question 24

Chord Conductance Model cuurent eqn:

Answer 24

All currents sum to 0 ( in parallel)

Question 25

Chord Conductance Model Membrane potential is the weighted mean of the different
equilibrium potentials, the weighting dependent on

Answer 25

the

conductance – an anolgue of the membrane permeability