Module 4 - Intro to Resting Membrane Potential

Question 1

What are the three types of potentials to consider?

Answer 1

Resting membrane potential
Action potential
Graded potential

Question 2

What is RMP?

Answer 2

The membrane voltage when the neuron/cell is at rest.

Question 3

What are action and graded potentials?

Answer 3

Are fluctuations from RMP caused by the opening of ion channels.

Question 4

What does excitation equate to?

Answer 4

Depolarization from RMP

Question 5

What does inhibition equate to?

Answer 5

Hyperpolarization from RMP

Question 6

What types of cells have more polarized RMPs? What is their RMP range?

Answer 6

Neurons, muscle and glial
-30 to -90 mV

Question 7

What types of cells have less polarized RMPs? Give examples and state their range.

Answer 7

Non-excitable cells
e.g., epithelial, RBCs
-8 to -30 mV

Question 8

What three things do ion pumps and exchangers ensure in all living cells (including bacteria)?

Answer 8

K+ is more abundant inside than outside
Na+ is more abundant outside than inside
Ca2+ is very low inside

Question 9

What ion concentration gradient can vary during development?

Answer 9

Cl-

Question 10

Why must Ca2+ be very low inside the cell

Answer 10

Toxic: precipitates proteins and organic/inorganic ions

Question 11

How do sea water animals differ in terms of ion concentrations compared to mammals?

Answer 11

Have more than double the ion concentrations compared to mammals

Question 12

How are mammals and sea water animals similar in terms of ions?

Answer 12

Roughly the same ratios across the membrane, K+ more abundant inside and Na+ more abundant outside.

Question 13

What type of energy acts on ions in a cell?

Answer 13

Electrical potential energy (voltage)
Random kinetic energy

Question 14

What does the total energy for moving a given ion through an aqueous cellular environment come from?

Answer 14

Voltage (Vm)
Concentration gradient of that ion.

Question 15

What determines the direction of an ion’s flow?

Answer 15

The balance between its gradient and the membrane voltage.

Question 16

What does the Nernst equation calculate?

Answer 16

The membrane voltage for a given ion concentration gradient where movement of ions stops (i.e., equilibrium potential).

Question 17

What is the equilibrium potential?

Answer 17

A voltage that exactly opposes the diffusion energy of an ion gradient.

Question 18

Give the Nernst equation and define the variables.

Answer 18

Eion = RT/zF ln([ion]out/[ion]in)
R - gas constant
T - absolute temperature in K
z - valence of the ion
F - faraday constant

Question 19

What is the thermodynamic gas constant?

Answer 19

8.31 J/mol K

Question 20

How is absolute temperature calculated?

Answer 20

celsius + 273.15

Question 21

What is the Faraday constant?

Answer 21

9.65 E4 C/mol

Question 22

What is the approximate value of RT/zF for a monovalent cation at 20 deg C?

Answer 22

~ 25 mV

Question 23

Which ion gradients are better able to control Vm?

Answer 23

Those that flow more quickly across the cell membrane.

Question 24

What is the RMP of most neurons and muscle cells?

Answer 24

Close to EK

Question 25

Why are most neurons and muscle cells' RMP close to EK?

Answer 25

Cells are generally more permeable to K+ at rest compared to other ions, due to an abundance of K+ leak channels.

Question 26

What was the hypothesis of Julius Bernstein?

Answer 26

RMP depends only on [K+]out vs. [K+]in, and thus EK

Question 27

Who developed the squid giant axon preparation?

Answer 27

John Zachary Young

Question 28

Why was the squid giant axon a popular choice for electrophysiological experiments?

Answer 28

It was so large, one could easily insert a recording electrode along its length

Question 29

Who tested Bernstein's hypothesis with the squid giant axon?

Answer 29

Hodgkin and Horowicz

Question 30

If Bernstein was right, what should have been the results of Hodgkin and Horowicz's experiment?

Answer 30

Changing [K+]out while keeping [K+]in constant would change EK, and RMP/Vm should follow EK

Question 31

What did Hodgkin and Horowicz actually see?

Answer 31

Hypothesis was supported at high [K+]out concentrations But showed an exponential relationship at near physiological [K+]out

Question 32

Why were Hodgkin and Horowitz's findings different than expected?

Answer 32

As EK pulls away from ENa, Na+ ions are further from equilibrium, flowing faster into the cell and countering the K+ currents.

Question 33

What does the driving force of an ion consist of?

Answer 33

Membrane voltage and that ion's concentration gradient

Question 34

What happens when Vm is not equal to Eion?

Answer 34

There is energy/driving force for ion flow.

Question 35

What happens when Ohm's Law and the Nernst equation are combined?

Answer 35

Defines the net energy acting on a given ion type in solution to produce a current.

Question 36

What is the equation wed get when combining Ohm's Law and the Nernst equation? Define the variables.

Answer 36

Iion = (Vm - Eion) * Gion Iion - ion current/flow Vm = membrane voltage Eion = ion's equilibrium potential Gion = conductance for that ion

Question 37

What is the equation for driving force?

Answer 37

Vm - Eion

Question 38

Using the equations/principles of IK and INa, describe how K and Na can both influence Vm.

Answer 38

K+ has a higher membrane conductance (GK>GNa), permitting larger current (IK), and hence a stronger influence on Vm. But as EK becomes more negative and pulls Vm further from ENa, the driving force for Na+ current (Vm-ENa) increases. Thus, Na+ ions can exert more control over Vm at negative voltages to counter the K+ effect.

Question 39

EXERCISE EK is -70 mV Vm = -70 mV How much driving force is there for moving K+ across the cell membrane? In which direction would K+ flow?

Answer 39

0 mV No net flux of ion across membrane.

Question 40

EXERCISE EK = -70 mV Vm = 0 mV How much driving force is there for moving K+ across the membrane? In which direction would K+ flow?

Answer 40

+70 mV Outward: +ve values for DF equate to outward cation flow.

Question 41

EXERCISE EK = -70 mV Vm = -90 mV How much driving force is there for moving K+ across the cell membrane? In which direction would K+ flow?

Answer 41

-20 mV Inward: -ve values for DF equate to inward cation flow.

Question 42

EXERCISE Half the K+ leak channels are removed from the membrane. What happens to GK? What happens to the K+ current? What if all K+ channels were removed?

Answer 42

GK and IK drop by half No more K+ current

Question 43

EXERCISE ENa = +70 mV Vm = 0 How much driving force is there for moving Na+ across the cell membrane? In which direction would Na+ flow?

Answer 43

-70 mV Inward: -ve values for DF equate to inward cation flow

Question 44

EXERCISE ENa = +70 mV Vm = +90 mV How much driving force is there for moving Na+ across the cell membrane? In which direction would Na+ flow?

Answer 44

+20 mV Outward: +ve values for DF equate to outward cation flow.

Question 45

EXERCISE EK is -50 mV ENa is +50 mV Vm = 0 mV Which ion has the greatest driving force? Which ion has the larger current? In which direction would the net flux of ions be greatest? What would happen to Vm?

Answer 45

Conductance for K+ higher than Na+, thus more DF for K+. K+ has larger current Flux outwards would be greatest Vm would become more negative.

Question 46

EXERCISE EK = -50 mV ENa = +50 mV Vm = 0mV GNa = 0 What would happen to Vm?

Answer 46

Since nothing is countering EK, Vm would drop to -50 mV.

Question 47

EXERCISE EK is -50 mV ENa = +50 mV Vm = 0 mV GK - 0 What would happen to Vm?

Answer 47

Since nothing is countering ENa, Vm would rise to +50 mV.