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Membrane Potential Flashcards

1
Q

What are the 2 cell types that have specialized use of membrane potentials?

A

Muscle cells

Neurons

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2
Q

In general, what is the function of dendrites? What is the function of axons?

A

Dendrites receive sensory information and carry it to the cell body

Axons carry information away from the cell body

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3
Q

What are the 2 subdivisions of the CNS?

A

Brain and spinal cord

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4
Q

What is the function of the CNS?

A

Receive, modify and transmit information

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5
Q

What is the function of the PNS?

A

Connect the brain and spinal cord to the limbs and organs

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6
Q

The […] is a layer of connective tissue that surrounds each individual axon.

A

Endoneurium

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7
Q

Label this diagram.

A
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8
Q

Axons are bundled together into groups called […]

A

Fasicles

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9
Q

Each fasicle is wrapped in a layer of connective tissue called the […]

A

Perineurium

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10
Q

The entire nerve is warpped in a layer of connective tissue called the […]

A

Epineurium

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11
Q

Only select cells in the body display membrane potential.

True/False

A

False - all cells do

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12
Q

What is membrane potential?

A

A separatin of positive and negative charges across the cell membrane

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13
Q

[…] transmit a particular kind of signal, the nerve impulse or action potential.

A

Axons

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14
Q

Cells capable of generating and conducting action potentials have an […] membrane.

A

Excitable

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15
Q

What is resting membrane potential?

A

When an excitable cell is at rest, there is a difference in electrical charge across the membrane

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16
Q

What are the 3 major factors that generate the resting membrane potential?

A
  • Charge carriers (water and ions)
  • Membrane is an impermeable barrier
  • Ion channels
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17
Q

It would take years for charged particles to spontaneously diffuse across a plasma membrane. How then do they cross?

A

Through ion channels

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18
Q

What 2 things define the selectivity of ion channels?

A
  • Diameter
  • Inner surface properties
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19
Q

What are the 3 subtypes of ion channels?

A
  • Ligand gated
  • Voltage gated
  • Leak channels (always open)
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20
Q

What is the difference between an ion channel and an ion pump?

A

When open, an ion channel lets molecules move freely according to their concentration gradients (diffusion and EMF). An ion pump uses energy (ATP) to actively transport ions across a membrane against a concentration gradient.

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21
Q

What makes ions pass through ion channels?

A
  • Diffusion
  • Electromotive Force (EMF)
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22
Q

What is the EMF?

A

In an electrical field, charged particles will move. The separation of charge on the inside vs. outside of the membrane creates an electrical field due to a difference in potential.

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23
Q

[…] = rate of flow of charge carriers

A

Current

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24
Q

[…] = electrical pressure

A

Voltage

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25
Q

[…] = ease of passage

A

Resistance

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26
Q

[…] = relative ability of charge carrier to migrate from one point to another

A

Conductance

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27
Q

What is ohm’s law?

A

V = IR

or

I = V/R

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28
Q

What is the resting membrane potential of a typical neuron?

A
  • 60mV to -70mV
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29
Q

Large changes in membrane potential are caused by […] change in ion concentration.

A

Miniscule

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30
Q

At the inside and outside surface of the cells there is a net difference in charges, but that difference dissipates the further you move into the ECM and the cytoplasm.

True/False.

A

True

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31
Q

What 3 things determine the equilibrium potential for an ion?

Of these 3 things, which is the most important for determining the size of the equilibrium potential?

A
  • Charge
  • Temperature
  • Concentration gradient
  • The greater the difference in concentration, the more electrical force is needed to counteract it and the higher the equilibrium potential. Temperature really does not contribute much and charge contribute little relative to concentration.
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32
Q

How is membrane potential established?

A

By ion pumps

Na+/K+ pump uses ATP to exchange 3Na+ for external K+ against their respective concentration gradients

Ca2+ pump works in a similar fashion

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33
Q

What determines whether the sign of the equilibrium potential is + or - ?

A
  • If there is more + charge inside than outside the cell –> result will be +
  • If there is more - charge inside than outside the cell –> result will be -
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34
Q

There is more […] inside than outside the cell.

There is less […] inside than outside the cell.

A

K+

Na+, Ca2+, Cl-

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35
Q

What is the equilibrium potential?

A

The point at which the forces of difussion that are pushinng an ion to leave the cell are = to the forces of EMF trying to make the ion enter the cell

36
Q

Given that there are multiple ions that contribute to the membrane potential, why is it that the value of -60mV to -70mV happens to be closest to the equilibrium potential of K+, which is -80mV?

A

This happens because the membrane is more permeable to K+ than Na+ so K+ potential contributes more to the overall membrane potential than Na+

37
Q

What is the difference between an equilibrium potential and a membrane potential?

A

Eq potential refers to the balance of diffusion and EMF as applied to a single ion

Membrane potential refers to the balance of diffusiona nd EMF as applied to all ions in environment

38
Q

What is an action potential?

A

A brief reversal of the resting membrane potential.

39
Q

The […] and […] of action potentials is the way neurons encode information.

A

Frequency and pattern

40
Q

All action potentials generated by a cell are about equal in size (amplitude) and duration.

True or False.

41
Q
  • What are 3 ways that an action potential can be generated?
  • Which of these is most potent?
A
  • Changes in temperature, ionic conductance, and ion concentration gradients
  • Change in conductance
42
Q

The membrane potential is sensitive to changes in the […] of K+ and Na+

A

Concentration

43
Q

An increase in the extracellular K+ concentration will make the K+ equilibrium potential […] and thus make the resting potential […] as well.

A

Less negative

44
Q

Increasing extracellular […] depolarizes the cell

45
Q

[…] cells dissipate excess extracellular K+ should it accumulate

47
Q

Action potentials are caused by depolarization of the membrane beyond a […].

48
Q

What are somethings that can cause the depolarization of the membrane up to the threshold?

A
  • Na+ entering the cell after a neurotransmitter has been released by another
  • Injecting current through a microelectrode
49
Q

After the depolarization crosses the threshold, the action potential unfolds automatically in an […] fashion

A

All or none

50
Q

What can happen if signals for depolarization are continuous?

A

More than one action potential may be triggered, however, it is impossible to trigger another one for 1ms (absolute refractory period).

51
Q

Increased current = […] frequency

52
Q

Describe the progression of an idealized action potential.

A
  • Begins with the idealized neuron at rest where the membrane is much more permeable to K+ than Na+ so the resting membrane potential is closer to that of K+ than Na+.
  • A signal (neurotransmitter, current, etc.) causes more Na+ channels to open and make the membrane more permeable to Na+ than K+. Na+ flows into the cell and the membrane potential moves toward that of Na+.
  • Once the membrane reache the potential of Na+, the Na+ channels close and the K+ channels open allowing the potential to move back towards that of K+.
  • The membrane potential continues until it returns to the potential of K+ which is -80mV. This is the undershoot. The amount of time for the neuron to return to the resting membrane potential from the undershoot is ~1ms or the absolute refractory period.
53
Q

The voltage gated sodium channel opens if it senses that the membrane potential has increased from -65mV to […]

54
Q

Describe the 4 phases of the sodium channel.

55
Q

What is tetrodotoxin?

Why is this substance toxic?

What are the first signs of poisoning?

A
  • A compound found in pufferfish (and other types of aquatic life) that covalently binds to sodium channels and blocks them from functioning
  • It can cause an inability to contract muscle –> inability to breathe
  • Numbness and tingling on the lips / mouth
57
Q

Once initiated, action potentials propogate along an axon in all directions simultaneously.

True or False.

A

False - they propogate in only one direction

58
Q

The […] the axon, the faster it propogates an action potential.

59
Q

What is the purpose of a myelin sheath?

A

To facilitate current flow and increase propagation speeds

60
Q

Myelinated axons propagate action potentials through […] conduction.

A

Saltatory - the action potentials jump from node of ranvier to node of ranvier

64
Q

How is membrane potential restored after hyperpolarization?

A

By the action of Na+/K+ ion pumps

65
Q

Only membranes that contain sufficient […] are capable of generating action potentials.

A

Voltage gated Na+ channels

66
Q

Describe what is happening in this image.

A

There are insufficient Na+ and K+ channels present in more distal parts of the axon to propagate the action potential so the AP does not continue to reach threshold as it travels down the axon.

67
Q

What are the 4 different “sizes” of axons?

68
Q

What substance is myelin made of?

A

Lipid (mostly)

69
Q

Active currents are only generated in short intervals of naked axonal membrane at the […]

A

Node of ranvier

70
Q

Where are K+ channels located?

A

Beneath the myelin

71
Q

Slow axons transmit information about […] and […]

A

Temperature and pain

72
Q

Fast axons transmit information about […]

73
Q

Describe how unmyelinated axons are myelinated.

74
Q

[…] Occur in both grey and white matter. Their function is to provide the electrochemically insulating myelin to all but the smallest axons in the white matter.

A

Oligodendrocytes

77
Q

In […] groups of oligodendrocytes and their myelin segments degenerate and are replaced by astrocytic plaques.

A

Multiple sclerosis

78
Q

What is an EPSP

A

Excitatory postsynaptic potential

A transient membrane depolarization caused by presynaptic release of neurotransmitter

79
Q

What is an IPSP

A

Inhibitory postsynaptic potential

Transient membrane hyperpolarization caused by presynaptic release of neurotransmitter

80
Q

A […] transient membrane depolarization at the axon hillock is required to initiate an action potential

A

Sufficiencly large

81
Q

Describe how transient depolarizations can cause an action potential.

A

They can undergo summation via constructive or destructive interference if they encounter one another. Summation events that reach threshold at the axon hillock will trigger action potentials.

83
Q

Real neurons are not as simple as the single axon diagram we’ve been talking about. What happens to the action potential in a neuron like this one?

A

We can think of the AP as splitting at the branch points and an exact copy of the AP being transmitted down each branch of the axon

84
Q

What happens to APs when an axon is demyelinated?

A

There is an interruption in the propagation of the AP down these axons

85
Q

How does demyelination affect the lifespan of a neuron?

A

The demyelinated axons survive temporarily and for some of them remyelination is possible by the growth of new oligodendrocytes.

86
Q

In general, are nerves in the CNS myelinated or unmyelinated?

A

Myelinated

MSK (38 decks)

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