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BMS03 > Electrical Properties Of Cell Membranes > Flashcards

Electrical Properties Of Cell Membranes Flashcards

1
Q

What is the resting potential of a typical cell?

A

-70mV

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2
Q

What ions principally determine resting membrane potential?

A

Na+

K+

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3
Q

What is the equilibrium potential?

A

Membrane potential that prevents movement of a given ion down its concentration gradient

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4
Q

If you make the intracellular membrane potential very negative, which ion’s net movement will change and how?

A

K+

Stops leaving

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5
Q

If you make the intracellular membrane potential very positive, which ion’s net movement will change and how?

A

Na+

Stops entering

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6
Q

For physiological concentrations, what is the equilibrium potential of K+?

A

-90mV

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7
Q

For physiological concentrations, what is the equilibrium potential of Na+?

A

+50mV

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8
Q

What is the Nernst equation?

A

E = RT/zF . ln [concentration gradient]

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9
Q

What is the Nernst equation at physiological concentrations for monovalent ions?

A

58 log [concentration gradient]

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10
Q

How do you calculate the concentration gradient of a positive ion?

A

[ion outside]/[ion inside]

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11
Q

How do you calculate the concentration gradient of a negative ion?

A

[ion inside]/[ion outside]

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12
Q

Why is resting membrane potential so much closer to E(K) than E(Na)?

A

Membrane is 50x more permeable time K+ than Na+ (more open K+ channels open at rest)

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13
Q

What is the net flow of ions at constant membrane potential?

A

0

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14
Q

If a membrane becomes permeable to an ion, what will happen?

A

The ion will move down its concentration gradient

Drive the membrane potential to its own equilibrium potential

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15
Q

How do you calculate the driving force on an ion (across a membrane)?

A

Driving force = Vm - E(eq)

Vm - membrane potential

E(eq) - equilibrium potential for that ion

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16
Q

What is the driving force on K+ ions at rest?

A

(Driving force = -70 - (-90) = +20mV)

+20mV forcing K+ out

17
Q

What is the driving force on Na+ ions at rest?

A

(Driving force = -70 - (+50) = -120mV)

-120mV forcing Na+ in

18
Q

Why is the resting membrane potential closer to E(K) when the driving force on Na+ is so much greater?

A

Membrane is much more permeable (50x) to K+ than Na+

Less force required to force the same number of K+ out than Na+ in

19
Q

What is permeability?

A

Ease with which an ion can cross the membrane (no. of open channels)

20
Q

What is conductance?

A

What actually gets across the membrane in terms of current/flow of ions

21
Q

How would a lower concentration gradient affect an ion’s conductance?

A

Lower driving force

Lower conductance (altered E(K))

22
Q

How would a decreased permeability affect an ion’s conductance?

A

Decreased conductance

23
Q

What is the Goldman Hodgkin Katz equation?

A

Vm = 58 log { (PK.[K+ outside] + PNa.[Na+ outside]) / (PK.[K+ inside] + PNa.[Na+ inside]) }

24
Q

Why is the Goldman Hodgkin Katz better than the Nernst equation?

A

Considers relative permeabilities of each ion

25
Q

What triggers an action potential?

A

Depolarisation to threshold (suprathreshold depolarisation)

26
Q

Why does the membrane potential become more positive during an action potential?

A

Voltage-gated Na+ channels open

Na+ moves into cell down concentration gradient

Pushes membrane potential to E(Na)

27
Q

What is the absolute refractory period?

A

From peak depolarisation to hyperpolarisation

28
Q

What is the relationship between conductance and resistance?

A

Conductance = reciprocal of resistance

29
Q

How long does an action potential take?

A

~4ms

30
Q

How does the action potential line relate to the Na+ conductance line on a conductance/time graph?

A

Action potential line is always above Na+ conductance (for duration of the Na+ movement)

31
Q

How does the action potential line relate to the K+ conductance line on a conductance/time graph?

A

Peak of K+ conductance is midway up the repolarisation slope of the action potential

32
Q

Which direction does current move?

A

Positive to negative

BMS03 (12 decks)

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