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EXCI 258 > Membrane Resting Potential and Action Potential > Flashcards

Membrane Resting Potential and Action Potential Flashcards

1
Q

Why is there no energy required in simple diffusion?

A

Because of the concentration gradient

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2
Q

T/F Sodium and Potassium are moved with the concentration gradient in active transport

A

False, they are moved against the concentration gradient

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3
Q

What is the resting membrane potential?

A

-90 mv

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4
Q

Describe what would happen if the membrane was only permeable to K+

A

K+ would diffuse down its concentration gradient until the electrical potential across the membrane counters the K+ diffusion (concentration difference = electrical difference)

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5
Q

What is the electrical potential that counters net diffusion of K+?

A

Equilibrium or Nernst Potential for K+

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6
Q

Define Nernst Potential

A

The electrical diffusion potential across a membrane that EXACTLY opposes the net diffusion of a particular ion through the membrane

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7
Q

What is the Nernst equation?

A

EMF = +/- 61 log (concentration inside/ concentration outside)

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8
Q

What determines if the 61 is positive or negative in the Nernst equation?

A

The sign is positive if the ion diffusing is negative and it is negative if the ion is positive

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9
Q

What is the electrical potential that counters net diffusion of K+?

A

-94 mv

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10
Q

If thee membrane was only permeable to K+ what would the membrane potential be?

A

-94 mv

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11
Q

How are the molecules kept inside and outside of the cell?

A

with unequal concentrations

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12
Q

Describe the extracellular fluid

A

High in Na+, Ca 2+ and Cl-, positively charged

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13
Q

Describe the intracellular fluid

A

high in K+, Mg 2+, proteins, negatively charged

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14
Q

Describe what would happen if the membrane was only permeable to Na+

A

Na+ would diffuse down its concentration gradient until a potential across the membrane (diffusion potential) counters the Na+ diffusion

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15
Q

What would the electrical potential that counters the net diffusion of Na+ be?

A

+61 mv

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16
Q

What is the Goldman (Goldman Hodgkin-Katz) equation?

A

EMF = -61 log (CNa+i PNa+ +Ck+i PK +CClo/ CNa+ o + PK+ CCli PCL-)

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17
Q

What does the membrane potential to several different ions depend on?

A

Concentration of respective ions on the inside and outside of the membrane
Permeability of membrane to each ion
Polarity of the electrical charge of ions positive or negative

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18
Q

Why is Vm so close to Ek?

A

Because the membrane is much more permeable to K+ than Na+

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19
Q

Which ion are leak channels more permeable to?

A

They are more permeable to K+ than Na+

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20
Q

What is the resting membrane potential for large nerve fibers (motorneurons) and small neurons

A

Large nerve fibers: -90 mv
Small neurons: -70 mv

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21
Q

What does the resting membrane potential of nerves depend on?

A
  1. Diffusion of potassium and sodium ions
  2. Permeability of ions through leak channels (P to K+&raquo_space; P to Na+ (100 times)
  3. Na+/ K+ pump (creates more negativity inside (transports 3 Na+ to outside vs 2 K+ to inside))
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22
Q

What is the take home message about membrane potential?

A

The resting membrane potential is closer to the equilibrium potential for the ion with the highest permeability (K+)

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23
Q

What are synonyms for Action Potential?

A

Spike, impulse or firing

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24
Q

Define an AP

A

A very rapid change in the membrane potential from “-“ to “+” values and return back to initial resting potential level

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25
Q

T/F the amplitude of an AP never changes

A

true

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26
Q

What are the two functions of Action Potentials?

A

1.Transmitting nerve signals

2.Rapid transmission over distance

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27
Q

What does speed of transmission depend on?

A

fiber size and whether it is myelinated (bigger size = faster transmission)

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28
Q

What are the 5 sequences of events for a nerve action potential?

A
  1. Resting stage
  2. Depolarization
  3. Repolarization
  4. Afterpotential
  5. Back to resting stage
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29
Q

What is the Vm aat the resting stage?

A

-90 mv

30
Q

What causes depolarization?

A

A sudden opening of Na+ channels, Na+ ions flow to inside the cell

31
Q

How long does the depolarization phase last?

A

0.1 ms

32
Q

What is the Vm in the repolarization phase?

A

+35 mv to -90 mv

33
Q

In what phase do Na+ channels begin to close and the K+ channels begin to slowly open?

A

Repolarization

34
Q

Why do the Na+ channels close and the K+ channels start to open?

A

to re-establish negative resting potential

35
Q

What is the Vm in the afterpotential?

A

<-90 mv

36
Q

Name synonyms for afterpotential

A

Hyperpolarization, undershoot

37
Q

What causes the afterpotential?

A

The K+ channels remain open for a few milliseconds after repolarization of the membrane is completed, excess K+ flows out of the membrane

38
Q

What causes the Vm to go back to resting stage?

A

The closing of the K+ channels

39
Q

What two protein channels cause the different staves of the action potential?

A

Voltage-gated Na+ channels
Voltage-gated K+ channels

40
Q

What type of diffusion are volatge gated channels?

A

Simple diffusion

41
Q

What are the two gates in a voltage gated sodium channel and where are they located?

A

Activation gate: exterior side of membrane

Inactivation gate: Interior side of membrane

42
Q

What are the three states of the voltage-gated sodium channels and which gates are open and closed?

A

Resting state: Activation closed & inactivation opens

Activated state: Both are open

Inactivated state: Activation open & inactivation closed

43
Q

T/F, during the resting state there is entering of Na+ ions

A

False

44
Q

What triggers the opening of the activation gate?

A

The shifting of membrane potential towards + values

45
Q

What is the opening threshold in the activated (depolarization) state?

A

-70 mv and -50 mv

46
Q

T/F the permeability to Na+ increases to 500 to 5000 times in the activated state

A

True

47
Q

Which stage of the action potential are the activated and inactivated states associated with?

A

Activated = depolarization
Inactivated = repolarization

48
Q

When is the inactivation gate activated?

A

When the membrane potential increases above 0 mv (overshoot)

49
Q

What is the refractory period?

A

When the inactivation gates do not re-open until the membrane returns to resting potential

50
Q

T/F there is more than one gate in the voltage-gated potassium channel

A

False, there is only one gate

51
Q

What are the two states in the voltage-gated potassium channel and what is the state of each gate?

A

Resting state: Gate closed
Slow activation state: Gate open

52
Q

What is another word for the slow activation state?

A

Repolarization

53
Q

What is overshoot?

A

When the K+ channels are activated when the membrane potential increases above 0

54
Q

Describe what occurs during the afterpotential

A

K+ channels remain open for a few ms after repolarization, excess K+ flow out of cell

55
Q

What is the resting membrane potential?

A

-90 mv

56
Q

What are mirror neurons referred to as?

A

Empathy neurons

57
Q

What is the threshold of initiation?

A

The level of membrane potential at which the positive-feedback cycle is created (point of no retunr)

58
Q

When does the threshold of initiation occur?

A

When the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve

59
Q

What are the three factors that can cause the initial increase in membrane potential?

A

Electrical stimulation, mechanic stimulation, chemical stimulation

60
Q

Explain the “all-or-none” principle

A

AP= signal either occurs fully or not at all

61
Q

T/F the frequency of firing (# of APs) is dependent on the intensity of the stimulus?

A

True

62
Q

Can an action potential occur if the membrane is still depolarized from the preceding AP? why or why not?

A

Np because Na+ channels are inactivated and the membrane needs to return to near original or resting potential to allow inactivation gates to reopen

63
Q

In which period can a new AP occur?

A

The relative refractory period

64
Q

What is myelin produced as an extension of?

A

Glial cells

65
Q

What are the glial cells in the PNS and CNS?

A

Schwann cells (PNS)
Oligodendrocytes un the (CNS)

66
Q

What insulates the nerve fibers?

A

Myeline sheath

67
Q

What interrupts the myelin sheath once every 1-3 mm?

A

Nodes of Ranvier

68
Q

What is saltatory conduction?

A

Where APs can only occur at the nodes of Ranvier

69
Q

What are the speeds of the AP in an unmyelinated and myelinated axon

A

unmyelinated: 0.25 m/s
myelinated: 100 m/s

70
Q

What is Multiple Sclerosis?

A

An immune-mediated inflamatory disease that causes the demyelination of the CNS

71
Q

What are 3 symptoms of MS

A

Muscle weakness, loss of sensation and death

EXCI 258 (4 decks)

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