Membrane potentials Flashcards

1
Q

Where is sodium highest?

A

Outside the cell

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2
Q

Where is potassium highest?

A

Inside the cell

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3
Q

What does the equilibrium potential depend on?

A

Concentration gradient and electrical potential difference

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4
Q

What is an eqn used to estimate equilibrium potential for a given ion?

A

Nernst eqn

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5
Q

Approx. concentration of sodium outside the cell?

A

140mM

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6
Q

Approx. concentration of sodium inside the cell?

A

14mM

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7
Q

Approx. concentration of potassium inside the cell?

A

120mM

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8
Q

Approx. concentration of potassium outside the cell?

A

4mM

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9
Q

Typical equilibrium potential for sodium

A

+65mV

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10
Q

Typical equilibrium potential for potassium

A

-95mV

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11
Q

For uncharged substances, what is considered for equilibrium potential?

A

ONLY concentration gradient

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12
Q

How would you calculate the net driving force?

A

Membrane potential - Equilibrium potential

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13
Q

If the driving force is negative what happens?

A

Cations will enter the cell and anions will leave

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14
Q

If the driving force is positive what happens?

A

Anions will enter the cell and cations will leave

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15
Q

If the driving force is zero what happens?

A

No net movement

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16
Q

Movement of ions between the ECF and ICF causes what?

A

Ionic current

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17
Q

Ionic current is almost synonymous with what?

A

Conductance

18
Q

What 2 factors determine membrane potential?

A

Concentrations of ions across the cell membrane and permeabilities

19
Q

What eqn gives relation between the membrane potential and conc./permeabilities of ions?

A

Goldman

20
Q

What is an action potential?

A

Transient increase in sodium permeability; basic signal of the nervous system

21
Q

Describe the action potential phases

A
  • Resting membrane potential is around -70mv, depolarization starts to occur and once the sodium coming in hits the threshold an AP is generated
  • Depolarizing phase
  • Overshoot
  • Repolarizing phase
  • Undershoot/hyperpolarizing phase
22
Q

What is the depolarizing phase?

A

When the membrane potential becomes less negative than resting membrane potential

23
Q

What is the overshoot?

A

When the inside of the cell becomes positive in respect to the outside of the cell for a brief moment

24
Q

What is the repolarizing phase?

A

Membrane potential returns to resting level

25
Q

What is the undershoot/hyperpolarizing phase?

A

When repolarizing, the membrane potential becomes slightly more negative than the resting membrane potential

26
Q

Describe the sodium channels

A

2 gates - activation gate and inactivation gate
The activation gate is closed at resting but opens upon depolarization
The inactivation gate is open at resting but slowly closes upon depolarization

27
Q

The act of the inactivation gate closing slowly upon depolarization - thus a delayed decline in sodium permeability - is known as what?

A

Sodium channel inactivation

28
Q

Describe the potassium channels

A

Just one gate, that is closed at resting and opens to let potassium out of the cell upon depolarization

29
Q

Does the potassium gate open when the sodium activation gate does?

A

No, the potassium gate is slower to open

30
Q

What is the absolute refractory period?

A

The time right after an AP has been generated that no amount of stimulus could cause another AP to be fired
- Inactivation gates are closed

31
Q

What is the relative refractory period?

A

The time after the absolute refractory period where the cell is hyperpolarizing, and if the stimulus were large enough an AP could be generated, but the stimulus must be larger than usual

32
Q

What is accomodation?

A

When cell is held at depolarized level for a sustained manner - occurs bc inactivation gates of sodium close slowly and remain closed which causes an increased potassium conductance out of the cell and results in a net reduction in cell excitability

33
Q

Hyperkalemia

A

High potassium in ECF, can cause muscle spasms because the resting membrane potential is less negative = depolarized

34
Q

Hypokalemia

A

Low potassium in ECF hyperpolarizes the cell which makes the resting membrane potential more negative and makes it harder to fire an AP causing muscle weakness

35
Q

Hypokalemic periodic paralysis

A

Attacks occur suddenly and may be triggered after exercise, stress or a high carb meal - muscle weakness

36
Q

What does lidocaine do?

A

Blocks sodium channels and action potentials do not occur

37
Q

What properties of the axon determine the way APs propagate?

A

Time constant and length constant

38
Q

What is tau?

A

The shorter the tau, the faster the speed of the impulse propagation - thus you want low membrane resistance and capacitance

39
Q

What is lamda?

A

The longer the lamda, the less the loss of the signal will be and the farther down the axon the voltage will spread - thus you want a large diameter to lower the internal resistance

40
Q

What properties does myelination give?

A

Increases the membrane resistance and lowers the membrane capacitance thus increasing the conduction velocity - nodes of ranvier and saltatory conduction

41
Q

What happens due to multiple sclerosis?

A

Loss of myelin sheath, causes a decreased in lamda and membrane resistance and thus a loss in the signal, so failure to conduct APs

42
Q

What are the symptoms of multiple sclerosis?

A

Weakness in LE, numbness, paresthesia, blurred vision and pain with eye movements