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Y1 Fundamentals of Neuroscience and Pharmacology > L11: Membrane Excitability > Flashcards

L11: Membrane Excitability Flashcards

1
Q

What determines the resting membrane potential of a neuron?

A

The resting membrane potential is primarily determined by the relative permeability of the membrane to potassium (K+) and sodium (Na+), with K+ having greater permeability due to leak channels.

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2
Q

Why is the resting membrane potential closer to the equilibrium potential of potassium?

A

The membrane is more permeable to potassium than sodium at rest, driving the membrane potential closer to the potassium equilibrium potential (-80 mV).

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3
Q

What is the role of the sodium-potassium ATPase pump in membrane potential?

A

It maintains ionic gradients by pumping 3 Na+ out and 2 K+ into the cell, but it is not responsible for rapid changes in membrane potential during action potentials.

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4
Q

What does the Nernst equation calculate?

A

The Nernst equation calculates the equilibrium potential for a specific ion based on its concentration gradient across the membrane.

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5
Q

How does temperature affect the Nernst equation?

A

Temperature (in Kelvin) is a factor in the Nernst equation, influencing the calculated equilibrium potential.

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6
Q

What happens when a neuron reaches its threshold potential?

A

Voltage-gated sodium channels open, leading to a rapid influx of Na+ and depolarization of the membrane.

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7
Q

What causes the repolarization phase of the action potential?

A

Voltage-gated potassium channels open, allowing K+ to exit the cell, restoring a negative membrane potential.

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8
Q

What is hyperpolarization, and why does it occur?

A

Hyperpolarization occurs when the membrane potential becomes more negative than the resting potential, due to the slow closing of voltage-gated potassium channels.

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9
Q

What is the absolute refractory period?

A

It is the period during which no new action potential can be initiated because voltage-gated sodium channels are inactivated.

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10
Q

How does the relative refractory period differ from the absolute refractory period?

A

During the relative refractory period, a stronger-than-normal stimulus can initiate another action potential because some sodium channels have recovered.

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11
Q

What are potassium leak channels?

A

These are non-gated channels that allow potassium ions to move freely, contributing to the resting membrane potential.

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12
Q

How do voltage-gated sodium channels work during an action potential?

A

They open rapidly in response to depolarization, allowing sodium to enter the cell, and then quickly inactivate.

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13
Q

What role do ligand-gated ion channels play in depolarization?

A

Ligand-gated channels open in response to neurotransmitter binding, allowing ions to flow and cause depolarization.

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14
Q

What happens to the equilibrium potential of an ion if its extracellular concentration increases?

A

The equilibrium potential shifts, becoming more positive for a cation or more negative for an anion.

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15
Q

Does the equilibrium potential of an ion change during an action potential?

A

No, it remains constant because it depends on ion concentrations, which are tightly regulated.

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16
Q

What determines the movement of ions across the membrane?

A

The movement of ions is determined by the chemical gradient (concentration difference) and the electrical gradient (membrane potential).

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17
Q

Why is permeability a key factor in membrane excitability?

A

Permeability dictates how ions move across the membrane, influencing the membrane potential and the ability of a neuron to reach the threshold for an action potential.

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18
Q

What is the significance of selective ion channels?

A

Selective ion channels allow specific ions to pass through, maintaining ion gradients and influencing the membrane potential.

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19
Q

What is the Goldman equation used for?

A

The Goldman equation calculates the membrane potential, taking into account the permeability and concentrations of multiple ions.

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20
Q

Why is potassium the dominant ion in the Goldman equation at rest?

A

The membrane is most permeable to potassium at rest, making it the primary determinant of the resting membrane potential.

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21
Q

What is threshold potential?

A

It is the membrane potential at which sodium influx exceeds potassium efflux, triggering an action potential.

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22
Q

What happens to voltage-gated sodium channels at the threshold potential?

A

They open rapidly, leading to a positive feedback loop and rapid depolarization.

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23
Q

What are the key phases of an action potential?

A

Depolarization, repolarization, hyperpolarization, and return to resting potential.

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24
Q

What causes the rapid depolarization phase?

A

The rapid influx of sodium ions through voltage-gated sodium channels.

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25
Q

Why does hyperpolarization occur after repolarization?

A

Voltage-gated potassium channels close slowly, allowing excess potassium to leave the cell.

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26
Q

What causes the absolute refractory period?

A

Inactivation of voltage-gated sodium channels prevents them from reopening immediately.

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27
Q

During the relative refractory period, what is required to initiate another action potential?

A

A stronger-than-normal stimulus to overcome hyperpolarization and reach the threshold.

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28
Q

How do sodium and potassium ions affect membrane potential during an action potential?

A

Sodium influx depolarizes the membrane, and potassium efflux repolarizes it.

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29
Q

What role does potassium play in hyperpolarization?

A

Potassium continues to leave the cell due to open voltage-gated potassium channels, driving the membrane potential below the resting level.

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30
Q

Why doesn’t ion movement during an action potential significantly alter ion concentrations?

A

Only a small number of ions move across the membrane during an action potential, leaving overall concentrations relatively unchanged.

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31
Q

What are the main types of ion channels in the neuron membrane?

A

Leak channels, voltage-gated channels, ligand-gated channels, and G-protein-coupled channels.

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32
Q

How do ligand-gated ion channels differ from voltage-gated ion channels?

A

Ligand-gated channels open in response to neurotransmitter binding, while voltage-gated channels open in response to changes in membrane potential.

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33
Q

What is the inactivation gate of a voltage-gated sodium channel?

A

A part of the channel that closes soon after the channel opens, stopping sodium influx and contributing to the refractory period.

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34
Q

How is the inactivation of sodium channels reversed?

A

It is reversed during repolarization, allowing the channel to return to a closed but activatable state.

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35
Q

Why is it important to understand the Nernst and Goldman equations in neuroscience?

A

These equations provide the mathematical foundation for understanding ion movement and membrane potential dynamics.

36
Q

How can misconceptions about ion movement be clarified?

A

By emphasizing that changes in membrane potential involve charge movement across the membrane, not significant changes in overall ion concentrations.

37
Q

What is the chemical driving force for ion movement?

A

It is the ion’s concentration gradient, moving ions from areas of high concentration to low concentration.

38
Q

What is the electrical driving force for ion movement?

A

It is the influence of the membrane potential, which attracts or repels ions based on their charge.

39
Q

What occurs when the chemical and electrical forces for an ion are balanced?

A

The ion reaches its equilibrium potential, and there is no net movement across the membrane.

40
Q

What determines how excitable a neuron is?

A

The proximity of the membrane potential to the threshold potential and the permeability of the membrane to specific ions.

41
Q

How does hyperpolarization affect excitability?

A

It decreases excitability by moving the membrane potential further from the threshold.

42
Q

What ion is primarily responsible for depolarizing the neuron during an action potential?

A

Sodium (Na+), through its influx during depolarization.

43
Q

Why is the sodium-potassium ATPase pump critical for maintaining membrane excitability?

A

It sustains the concentration gradients of sodium and potassium, essential for generating action potentials.

44
Q

What happens if the sodium-potassium pump is inhibited?

A

Ion gradients would gradually dissipate, leading to a loss of resting membrane potential and neuronal function.

45
Q

What happens to the membrane potential if permeability to sodium increases?

A

The membrane potential moves closer to the sodium equilibrium potential (+62 mV).

46
Q

Why doesn’t the equilibrium potential for potassium change during an action potential?

A

Because the intracellular and extracellular concentrations of potassium remain relatively constant.

47
Q

What causes the membrane potential to dip below resting levels during hyperpolarization?

A

The delayed closing of voltage-gated potassium channels, allowing excess K+ to exit the cell.

48
Q

How is the resting membrane potential restored after hyperpolarization?

A

Voltage-gated potassium channels close, and leak channels stabilize the potential at resting levels.

49
Q

What triggers voltage-gated ion channels to open?

A

Changes in the membrane potential, specifically depolarization.

50
Q

How do voltage-gated sodium channels contribute to the refractory period?

A

They inactivate after opening, preventing another action potential until they return to a closed state.

51
Q

What role do ligand-gated ion channels play in synaptic transmission?

A

They open in response to neurotransmitters, allowing ions to flow and initiate depolarization or hyperpolarization.

52
Q

How do ligand-gated channels differ from voltage-gated channels in their activation?

A

Ligand-gated channels are activated by chemical signals, while voltage-gated channels respond to electrical signals.

53
Q

Why is the depolarization phase so rapid?

A

Because of the positive feedback loop where opening voltage-gated sodium channels causes more sodium channels to open.

54
Q

Why does the action potential not move backward along an axon?

A

The inactivated state of sodium channels behind the action potential prevents reactivation.

55
Q

What ensures the unidirectional flow of action potentials?

A

The refractory periods of sodium channels.

56
Q

What is the functional purpose of the absolute refractory period?

A

To limit the frequency of action potentials and ensure discrete signaling.

57
Q

What conditions are necessary to overcome the relative refractory period?

A

A stronger-than-normal depolarizing stimulus.

58
Q

How does extracellular potassium concentration affect the resting membrane potential?

A

Increasing extracellular potassium reduces the concentration gradient, making the resting potential less negative.

59
Q

Why do ion concentrations remain stable during action potentials despite ion movement?

A

Because only a small fraction of ions cross the membrane during an action potential.

60
Q

What is the role of excitatory postsynaptic potentials (EPSPs)?

A

EPSPs depolarize the membrane, bringing it closer to the threshold for action potential generation.

61
Q

How do inhibitory postsynaptic potentials (IPSPs) affect membrane potential?

A

IPSPs hyperpolarize the membrane, moving it further from the threshold.

62
Q

What is required for a neuron to reach threshold and fire an action potential?

A

Sufficient depolarization from excitatory inputs, often through ligand-gated sodium channels or experimental stimulation.

63
Q

How does the concept of summation relate to synaptic inputs?

A

Summation refers to the combined effects of multiple excitatory or inhibitory inputs, either temporally or spatially, to influence whether the neuron reaches threshold.

64
Q

Why are voltage-gated potassium channels important during repolarization?

A

They allow potassium to exit the cell, restoring the membrane potential after depolarization.

65
Q

What is the role of inactivation gates in voltage-gated sodium channels?

A

They prevent further sodium influx during the refractory period, ensuring unidirectional propagation of action potentials.

66
Q

How does increased permeability to chloride affect the membrane potential?

A

It hyperpolarizes the membrane, as chloride influx makes the inside of the cell more negative.

67
Q

What happens to the membrane potential if permeability to both sodium and potassium is equal?

A

The membrane potential would lie between the equilibrium potentials of sodium (+62 mV) and potassium (-80 mV), closer to the ion with higher permeability.

68
Q

What does the Goldman equation incorporate that the Nernst equation does not?

A

It accounts for multiple ions and their relative permeabilities across the membrane.

69
Q

Why is chloride often included in the Goldman equation despite its minimal effect at rest?

A

Chloride contributes to the membrane potential, especially under conditions where its permeability changes.

70
Q

What are potassium leak channels, and why are they important at rest?

A

These are non-gated channels that allow potassium to move freely, setting the resting membrane potential closer to the potassium equilibrium potential.

71
Q

Why is the resting membrane potential not exactly at the potassium equilibrium potential?

A

There is a small permeability to sodium, which pulls the resting potential slightly more positive than the potassium equilibrium potential.

72
Q

What restores the membrane potential after hyperpolarization?

A

The closure of voltage-gated potassium channels and the dominance of potassium leak channels bring the potential back to resting levels.

73
Q

Why is hyperpolarization important for neuronal signaling?

A

It prevents immediate reactivation of the neuron, contributing to the refractory period and ensuring clear, discrete action potentials.

74
Q

How do myelination and nodes of Ranvier affect action potential propagation?

A

Myelination increases conduction speed by allowing the action potential to jump between nodes of Ranvier in a process called saltatory conduction.

75
Q

Why is action potential propagation unidirectional?

A

The refractory periods of sodium channels prevent backward movement of the action potential.

76
Q

How can artificial depolarization trigger an action potential?

A

By using an electrode to directly apply electrical current, the membrane potential can be brought to threshold.

77
Q

What is the role of practical experiments, such as stimulating a worm’s nerve, in understanding excitability?

A

These experiments demonstrate concepts like refractory periods, threshold, and action potential propagation in real-time.

78
Q

Why is the absolute refractory period critical for neuronal function?

A

It ensures that each action potential is a separate event and limits the maximum frequency of firing.

79
Q

How does the relative refractory period allow for stronger stimuli to generate an action potential?

A

During this period, some sodium channels recover, but the membrane potential is hyperpolarized, requiring a larger depolarizing stimulus to reach threshold.

80
Q

Why do ions move during an action potential without depleting their gradients?

A

Only a small fraction of ions cross the membrane, so bulk concentrations remain largely unchanged.

81
Q

What role does the extracellular environment play in neuronal excitability?

A

Changes in extracellular ion concentrations, especially potassium, can significantly alter resting membrane potential and excitability.

82
Q

What is depolarization?

A

A decrease in membrane potential making the inside of the cell less negative relative to the outside.

83
Q

What is repolarization?

A

The return of the membrane potential to its resting state after depolarization.

84
Q

What is the equilibrium potential of an ion?

A

The membrane potential at which there is no net movement of that ion across the membrane due to a balance between electrical and chemical forces.

85
Q

Why doesn’t the sodium-potassium pump directly contribute to the rapid changes during an action potential?

A

Its action is too slow to influence the fast dynamics of action potentials, which are driven by ion channel opening and closing.

86
Q

How can changes in experimental conditions (e.g., temperature) affect calculations of equilibrium potential?

A

Temperature affects the constants in the Nernst equation, altering the calculated equilibrium potential.

Y1 Fundamentals of Neuroscience and Pharmacology (11 decks)

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