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MCBM > MCBM Exam 3 Action potential > Flashcards

MCBM Exam 3 Action potential Flashcards

1
Q

What does the nervous system do?

A

sends both qualitative and quantitative info with the combination of electrical and chemical signals

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2
Q

What are the 2 main membrane domains in a neuron?

A

somatodendritic domain and axonal domain

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3
Q

What is a neuron?

A

a specialized cell type composed of specific membrane domains

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4
Q

What does each neuron have?

A

a specific physiological function due to the presence of specific proteins in the specific membrane domains

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5
Q

What is a dendrite?

A

a cell that receives incoming signals

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6
Q

What is an axon hillock?

A

an action potential generation zone

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7
Q

What is an axon?

A

impulse conduction (action potentials)

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8
Q

What happens at the nerve termini?

A

secretion of neurotransmitter

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9
Q

A neurons is a type of _________ cell

A

polarized

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10
Q

What are membrane domains?

A

distinct regions within a cell membrane where you find proteins that function in a common process grouped together

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11
Q

What do the plasma membrane of the nerve cell body and dendrites resemble?

A

the basolateral plasma membrane domain of a polarized epithelial cell

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12
Q

What does the somatodendritic domain include?

A

the membrane of the cell body (soma) and the extensions that receive incoming signals (dendrites)

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13
Q

What do the membranes of the somatodendritic domain contain?

A

receptors that will bind to incoming signals (neurotransmitters)

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14
Q

What happens when the receptors bind to incoming signals (neurotransmitters)?

A

the receptors are linked either directly or indirectly to ion channels whose opening leads to changes in membrane potential

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15
Q

What type of ion channel is directly linked to the incoming signal and will open the channel? (the receptor and channel are the same protein)

A

Ligand-gated ion channels

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16
Q

What is GPCR?

A

G- protein coupled receptor

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17
Q

What does GPCR do?

A

indirectly links the receptor which receives incoming signals to an ion channel via the activation of a G-protein which then leads to the opening of the ion channel (the receptor and ion channel are two different proteins that are physiologically coupled by the G- protein

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18
Q

What does the axonal domain include?

A

includes membranes from the axon hillock through to the nerve termini

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19
Q

What are the main voltage-gated ion channels involved in the production and propagation of action potentials in the axonal domain?

A

voltage-gated Na and K channels

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20
Q

Where is there a graded local response?

A

in dendrites and the cell body

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21
Q

What is a graded local response?

A

initial change in voltage due to opening of non-voltage-gated ion channels

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22
Q

What type of spread of voltage change is seen in a graded local response?

A

passive spread

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23
Q

Where does the all or none response occur?

A

from axon hillock to terminus

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24
Q

What is the all or none response?

A

refers to production of action potentials that occur due to presence of voltage-gated Na and K channels

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25
Q

In what way can somatodendritic domains respond to membrane potential?

A

can only respond passively to changes in membrane potential

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26
Q

What is the actual change (amplitude) in membrane potential will vary based on what?

A

the frequency of incoming signals, the relative density of open ion channels, the type of ion being conducted across the membrane and how far a part a membrane is from the original point source

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27
Q

The difference in the type of responses is due to what?

A

due to the absence or presence or voltage-gated Na and K channels, and thus the development (or lack there of) of an action potential

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28
Q

What is resting potential?

A

potential maintained across membrane of excitable cells (neurons, muscle)

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29
Q

What is hyperpolarization?

A

membrane potential more negative than the rest

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30
Q

What is depolarization?

A

membrane potential less negative or positive than the rest

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31
Q

What is threshold potential?

A

the level of depolarization that triggers an action potential

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32
Q

What is action potential?

A

a rapid, large regenerative depolarization

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33
Q

What is Ohms law?

A

V=IR

velocity=currentXresistance

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34
Q

What would stimulate hyperpolarization?

A

due to either an efflux of cations or an influx of anions which causes the Vm to become more negative than the resting potential

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35
Q

What would stimulate depolarization?

A

due to etiehr an influx of cation or an efflux of anion, causing Vm to become less negative than the resting potential

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36
Q

The amplitude of the voltage deflection across the membrane is proportional to what?

A

the amplitude of the stimulus pulse (the current) assuming constant resistance (V=IR)

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37
Q

If the stimulus is larger what else will be larger?

A

the voltage deflection

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38
Q

What is the amplitude of the voltage deflection variable and dependedt upon?

A

the stimulus intensity=graded potential

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39
Q

What type of potential can occur in any part of the membrane in any cell?

A

graded potential

40
Q

What can result from the process of summation where two or more stimuli affect the membrane potential over time or space?

A

graded potentials

41
Q

The magnitude of the voltage deflection is proportional to what?

A

the rate of current flow (leading to variable graded changes in membrane potential)

42
Q

In membrane domains that contain voltage-gated channels when is an action potential developed?

A

if the magnitude of the graded potential reaches threshold

43
Q

What is the minimum stimulus intensity NECESSARY to induce an action potential in an all or none action potential?

A

threshold stimulus

44
Q

Does increasing the amplitude of the stimulus above threshold cause an increase in the size of the voltage deflection of the action potential?

A

no increasing the amplitude of the stimulus does not cause an increase in the size of voltage deflection

45
Q

Where doe graded potentials typically occur?

A

usually dendrites and the cell body

46
Q

Where do the action potentials occur?

A

trigger zone through the axon

47
Q

What initiates the signal of a graded potential?

A

entry of ions through channels

48
Q

What initiates the signal of an action potential?

A

above-threshold graded potential at the trigger zone (refers to an in vivo response)

49
Q

What requires the presence or absence of voltage gated Na and K channels and maintenance of the resting Vm?

A

action potentials

50
Q

How small or large is the depolarization of an action potential?

A

can be brief (msec) or large (up to 100mV) of depolarization followed by a repolarization back to (or below) resting potential

51
Q

How does an action potential in the axonal membrane of a neuron occur?

A

a stimulus induces an initial depolarization that opens a few members of the population of voltage-gated Na channels present in the membrane

52
Q

What happens once the Vm has reached threshold?

A

the population of voltage gated sodium channels rapidly open leading to an increase in sodium permeability across the membrane

53
Q

What happens at the resting state during an action potential?

A

all voltage gated Na+ and K+ channels are closed

54
Q

What happens in the depolarizing phase during an action potential?

A

voltage-gated Na+ channels open

55
Q

What happens during the repolarizing phase during an action potential?

A

voltage-gated Na+ channels inactivate and K+ channels open

56
Q

What happens during the hyperpolarizing phase during an action potential?

A

K+ channels slowly close and Na+ channels are inactive

57
Q

What is conductance?

A

a measure of rate of ion flow proportional to Px X (Vm=-Ex)

58
Q

If the conductance is increase what else will increase?

A

the current for any given voltage across the membrane (gV=I)

59
Q

What is the change of conductance due to?

A

due to a change in permeability

60
Q

Are both the voltage-gated Na and voltage-gated K channels triggered independently?

A

yes they are triggered independently by the same approximate threshold voltage however their response time differs

61
Q

What would happen if the conductance to Na didn’t decrease?

A

the membrane potential would stay depolarized

62
Q

Which ions permeability is low and is non-variable in axonal membranes?

A

chloride

63
Q

At rest is permeability greater to K or to Na?

A

greater permeability to K due to the always open K leak channels that set the membrane potential

64
Q

What happens during the rising phase?

A

there is an increase in permeability to Na opening more Na+ channels

65
Q

What happens during the falling phase?

A

there is an increase in permeability to K and an inactivating of Na+ channels

66
Q

What leads to a characteristic membrane potential profile of an action potential?

A

the combined actinons of het opening of the voltage-gated Na channels followed by the slightly delayed opening of the voltage- gated K channels

67
Q

What is found in the skin and liver of puffer fish that blocks the fast voltage-gated Na+ channel of neurons and striated muscle?

A

tetrodotoxin (TTX)

68
Q

What affect would TTX have on the voltage changes associated with an action potential?

A

it would prevent an action potential from taking place

69
Q

What is needed to form the K+ channels?

A

four alpha subunits come together to make an oligomer beta subunits also associated with the cytoplasmic side of the channel

70
Q

How are both Na+ and Ca2+ channels thought to be derived?

A

from gene duplication events leading to the production of “pseudo-oligomers”

71
Q

What is each of the four domains comprised of in the voltage-gated Na channel?

A

comprised of six membrane spanning regions

72
Q

What does the 4th membrane spanning helix in each domain in the voltage-gated Na channel contain?

A

contains the voltage sensor for the channel protein

73
Q

How many gates are involved in the voltage-gated Na channel?

A

two gates: the voltage sensitive gate and an inactivation particle

74
Q

What are the two non- conducting states of the voltage-gated Na+ channel?

A

closed and inactivated

75
Q

What do closed channels of the voltage-gated sodium channel respond to?

A

depolarization

76
Q

Can the inactive channels of the voltage-gated sodium channel respond to depolarization?

A

no

77
Q

What happens to the channel of the voltage-gated Na+ channel when Vm is at rest?

A

the channel is closed

78
Q

What happens when the voltage-gated Na+ channel is depolarized?

A

the depolarization of the membrane induces a conformational change that opens the channel allowing Na+ to cross the membrane and further depolarize Vm

79
Q

Why does the channel spontaneously inactivate?

A

due to the non-conducting state when the channel is non-responsive to depolarization and cant open (happens after a period of time)

80
Q

What happens when Vm repolarizes?

A

the channel spontaneously revert back to its closed state and is capable of reopening

81
Q

What are the 3 stages of voltage-gated Na+ channels?

A

closed
open
inactive

82
Q

What happens during the closed stage of voltage-gated Na+ channels?

A

non-conducting, able to respond to a depolarization

83
Q

What happens during the open stage of voltage-gated Na+ channels?

A

conducting, unstable conformation and the channel will not stay in that conformation for long

84
Q

What happens during the inactive stage of voltage-gated Na+ channels?

A

non-conducting, unable to respond to depolarization will stay in this conformation until the membrane repolarizes and then spontaneously reverts to the closed configuration

85
Q

What is the Hodgkin cycle?

A

one of the few examples of positive feedback in biological systems

86
Q

What are two other examples of positive feedback in biological systems?

A

parturition, blood clotting

87
Q

What starts the Hodgkin cycle?

A

any stimulus that induces a membrane depolarization starts the cycle causing v.g. Na+ channels to open

88
Q

How does the positive feedback loop inactivate the channel?

A

it has to have an outside mechanism to stop the process

89
Q

What are refractory periods?

A

unresponsive periods

90
Q

When does a refractory period occur?

A

the membrane becomes refractory to further depolarization’s for a brief time after an action potential

91
Q

Why is there a refractory period?

A

due to the inactivation phase of the voltage gated Na+ channels

92
Q

Does a larger stimulus induce another action potential?

A

NOOO

93
Q

What is an absolute refractory period?

A

no action potential can be generaed and most v.g Na+ channels are still inactivated and unable to respond

94
Q

What is a relative refractory period?

A

a smaller than normal action potential can be generated in response to a larger stimulus

95
Q

What is the temperature that is the approximate threshold for pain?

A

43 degrees Celsius

MCBM (6 decks)

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