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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
In what way can somatodendritic domains respond to membrane potential?
can only respond passively to changes in membrane potential
26
What is the actual change (amplitude) in membrane potential will vary based on what?
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
27
The difference in the type of responses is due to what?
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
28
What is resting potential?
potential maintained across membrane of excitable cells (neurons, muscle)
29
What is hyperpolarization?
membrane potential more negative than the rest
30
What is depolarization?
membrane potential less negative or positive than the rest
31
What is threshold potential?
the level of depolarization that triggers an action potential
32
What is action potential?
a rapid, large regenerative depolarization
33
What is Ohms law?
V=IR | velocity=currentXresistance
34
What would stimulate hyperpolarization?
due to either an efflux of cations or an influx of anions which causes the Vm to become more negative than the resting potential
35
What would stimulate depolarization?
due to etiehr an influx of cation or an efflux of anion, causing Vm to become less negative than the resting potential
36
The amplitude of the voltage deflection across the membrane is proportional to what?
the amplitude of the stimulus pulse (the current) assuming constant resistance (V=IR)
37
If the stimulus is larger what else will be larger?
the voltage deflection
38
What is the amplitude of the voltage deflection variable and dependedt upon?
the stimulus intensity=graded potential
39
What type of potential can occur in any part of the membrane in any cell?
graded potential
40
What can result from the process of summation where two or more stimuli affect the membrane potential over time or space?
graded potentials
41
The magnitude of the voltage deflection is proportional to what?
the rate of current flow (leading to variable graded changes in membrane potential)
42
In membrane domains that contain voltage-gated channels when is an action potential developed?
if the magnitude of the graded potential reaches threshold
43
What is the minimum stimulus intensity NECESSARY to induce an action potential in an all or none action potential?
threshold stimulus
44
Does increasing the amplitude of the stimulus above threshold cause an increase in the size of the voltage deflection of the action potential?
no increasing the amplitude of the stimulus does not cause an increase in the size of voltage deflection
45
Where doe graded potentials typically occur?
usually dendrites and the cell body
46
Where do the action potentials occur?
trigger zone through the axon
47
What initiates the signal of a graded potential?
entry of ions through channels
48
What initiates the signal of an action potential?
above-threshold graded potential at the trigger zone (refers to an in vivo response)
49
What requires the presence or absence of voltage gated Na and K channels and maintenance of the resting Vm?
action potentials
50
How small or large is the depolarization of an action potential?
can be brief (msec) or large (up to 100mV) of depolarization followed by a repolarization back to (or below) resting potential
51
How does an action potential in the axonal membrane of a neuron occur?
a stimulus induces an initial depolarization that opens a few members of the population of voltage-gated Na channels present in the membrane
52
What happens once the Vm has reached threshold?
the population of voltage gated sodium channels rapidly open leading to an increase in sodium permeability across the membrane
53
What happens at the resting state during an action potential?
all voltage gated Na+ and K+ channels are closed
54
What happens in the depolarizing phase during an action potential?
voltage-gated Na+ channels open
55
What happens during the repolarizing phase during an action potential?
voltage-gated Na+ channels inactivate and K+ channels open
56
What happens during the hyperpolarizing phase during an action potential?
K+ channels slowly close and Na+ channels are inactive
57
What is conductance?
a measure of rate of ion flow proportional to Px X (Vm=-Ex)
58
If the conductance is increase what else will increase?
the current for any given voltage across the membrane (gV=I)
59
What is the change of conductance due to?
due to a change in permeability
60
Are both the voltage-gated Na and voltage-gated K channels triggered independently?
yes they are triggered independently by the same approximate threshold voltage however their response time differs
61
What would happen if the conductance to Na didn't decrease?
the membrane potential would stay depolarized
62
Which ions permeability is low and is non-variable in axonal membranes?
chloride
63
At rest is permeability greater to K or to Na?
greater permeability to K due to the always open K leak channels that set the membrane potential
64
What happens during the rising phase?
there is an increase in permeability to Na opening more Na+ channels
65
What happens during the falling phase?
there is an increase in permeability to K and an inactivating of Na+ channels
66
What leads to a characteristic membrane potential profile of an action potential?
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
What is found in the skin and liver of puffer fish that blocks the fast voltage-gated Na+ channel of neurons and striated muscle?
tetrodotoxin (TTX)
68
What affect would TTX have on the voltage changes associated with an action potential?
it would prevent an action potential from taking place
69
What is needed to form the K+ channels?
four alpha subunits come together to make an oligomer beta subunits also associated with the cytoplasmic side of the channel
70
How are both Na+ and Ca2+ channels thought to be derived?
from gene duplication events leading to the production of "pseudo-oligomers"
71
What is each of the four domains comprised of in the voltage-gated Na channel?
comprised of six membrane spanning regions
72
What does the 4th membrane spanning helix in each domain in the voltage-gated Na channel contain?
contains the voltage sensor for the channel protein
73
How many gates are involved in the voltage-gated Na channel?
two gates: the voltage sensitive gate and an inactivation particle
74
What are the two non- conducting states of the voltage-gated Na+ channel?
closed and inactivated
75
What do closed channels of the voltage-gated sodium channel respond to?
depolarization
76
Can the inactive channels of the voltage-gated sodium channel respond to depolarization?
no
77
What happens to the channel of the voltage-gated Na+ channel when Vm is at rest?
the channel is closed
78
What happens when the voltage-gated Na+ channel is depolarized?
the depolarization of the membrane induces a conformational change that opens the channel allowing Na+ to cross the membrane and further depolarize Vm
79
Why does the channel spontaneously inactivate?
due to the non-conducting state when the channel is non-responsive to depolarization and cant open (happens after a period of time)
80
What happens when Vm repolarizes?
the channel spontaneously revert back to its closed state and is capable of reopening
81
What are the 3 stages of voltage-gated Na+ channels?
closed open inactive
82
What happens during the closed stage of voltage-gated Na+ channels?
non-conducting, able to respond to a depolarization
83
What happens during the open stage of voltage-gated Na+ channels?
conducting, unstable conformation and the channel will not stay in that conformation for long
84
What happens during the inactive stage of voltage-gated Na+ channels?
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
What is the Hodgkin cycle?
one of the few examples of positive feedback in biological systems
86
What are two other examples of positive feedback in biological systems?
parturition, blood clotting
87
What starts the Hodgkin cycle?
any stimulus that induces a membrane depolarization starts the cycle causing v.g. Na+ channels to open
88
How does the positive feedback loop inactivate the channel?
it has to have an outside mechanism to stop the process
89
What are refractory periods?
unresponsive periods
90
When does a refractory period occur?
the membrane becomes refractory to further depolarization's for a brief time after an action potential
91
Why is there a refractory period?
due to the inactivation phase of the voltage gated Na+ channels
92
Does a larger stimulus induce another action potential?
NOOO
93
What is an absolute refractory period?
no action potential can be generaed and most v.g Na+ channels are still inactivated and unable to respond
94
What is a relative refractory period?
a smaller than normal action potential can be generated in response to a larger stimulus
95
What is the temperature that is the approximate threshold for pain?
43 degrees Celsius

MCBM (6 decks)

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