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BIO304 > Module 4 - Intro to Resting Membrane Potential > Flashcards

Module 4 - Intro to Resting Membrane Potential Flashcards

1
Q

What are the three types of potentials to consider?

A

Resting membrane potential
Action potential
Graded potential

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2
Q

What is RMP?

A

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

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3
Q

What are action and graded potentials?

A

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

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4
Q

What does excitation equate to?

A

Depolarization from RMP

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5
Q

What does inhibition equate to?

A

Hyperpolarization from RMP

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6
Q

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

A

Neurons, muscle and glial
-30 to -90 mV

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

What ion concentration gradient can vary during development?

A

Cl-

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10
Q

Why must Ca2+ be very low inside the cell

A

Toxic: precipitates proteins and organic/inorganic ions

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11
Q

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

A

Have more than double the ion concentrations compared to mammals

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12
Q

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

A

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

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13
Q

What type of energy acts on ions in a cell?

A

Electrical potential energy (voltage)
Random kinetic energy

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14
Q

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

A

Voltage (Vm)
Concentration gradient of that ion.

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15
Q

What determines the direction of an ion’s flow?

A

The balance between its gradient and the membrane voltage.

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16
Q

What does the Nernst equation calculate?

A

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

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17
Q

What is the equilibrium potential?

A

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

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18
Q

Give the Nernst equation and define the variables.

A

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

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19
Q

What is the thermodynamic gas constant?

A

8.31 J/mol K

20
Q

How is absolute temperature calculated?

A

celsius + 273.15

21
Q

What is the Faraday constant?

A

9.65 E4 C/mol

22
Q

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

A

~ 25 mV

23
Q

Which ion gradients are better able to control Vm?

A

Those that flow more quickly across the cell membrane.

24
Q

What is the RMP of most neurons and muscle cells?

A

Close to EK

25
Q

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

A

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

26
Q

What was the hypothesis of Julius Bernstein?

A

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

27
Q

Who developed the squid giant axon preparation?

A

John Zachary Young

28
Q

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

A

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

29
Q

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

A

Hodgkin and Horowicz

30
Q

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

A

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

31
Q

What did Hodgkin and Horowicz actually see?

A

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

32
Q

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

A

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

33
Q

What does the driving force of an ion consist of?

A

Membrane voltage and that ion’s concentration gradient

34
Q

What happens when Vm is not equal to Eion?

A

There is energy/driving force for ion flow.

35
Q

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

A

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

36
Q

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

A

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

37
Q

What is the equation for driving force?

A

Vm - Eion

38
Q

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

A

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.

39
Q

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?

A

0 mV
No net flux of ion across membrane.

40
Q

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?

A

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

41
Q

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?

A

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

42
Q

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?

A

GK and IK drop by half
No more K+ current

43
Q

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?

A

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

44
Q

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?

A

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

45
Q

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?

A

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.

46
Q

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

A

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

47
Q

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

A

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

BIO304 (13 decks)

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