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KINE2011: Human Physiology > Module 3: Lecture 3 > Flashcards

Module 3: Lecture 3 Flashcards

1
Q

what causes a graded potential?

A
  • some triggering event allows the response to change the cells membrane permeability
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2
Q

what is the action potential?

A

everything that occurs following the threshold potential being reached
- the depolarization and the repolarization phases back down to rest
- occurs very rapidly

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3
Q

because the action potential has so much amplitude, what does it reach during depolarization?

A

0mV and even positive mV membrane potential
- note: membrane potential at rest is -70mV

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4
Q

how fast is repolarization after a depolarization of action potential?

A

just as rapid as the depolarization

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5
Q

what is an overshoot?

A

the reversion period (‘reversing’ the potential above 0 mV)

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6
Q

how long is an action potential?

A

always the same duration
- 1 msec in a nerve cell

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7
Q

what is another name for an action potential?

A

a spike

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8
Q

when an excitable membrane is triggered to undergo an action potential, we say it?

A

‘fires’

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9
Q

what is the key to an action potential?

A

the change in membrane permeability to ions

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10
Q

which gated ion channel uses change of voltage/membrane potential as a mechanism of opening and closing triggering event?

A

voltage-gated channels

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11
Q

what is the triggering event of a mechanically gated ion channel?

A
  • open in response to mechanical deformation
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12
Q

what is the triggering event of a chemically gated ion channel?

A
  • open in response to some sort of molecule binding to the ion channel specifically neurotransmitters
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13
Q

which gated ion channel opens to initiate action potential?

A

voltage gated ion channels

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14
Q

what are the two voltage gated ion channels?

A
  1. voltage gated K+ (potassium) channels
  2. voltage gated Na+ (sodium) channels
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15
Q

how does a voltage gated K+ (potassium) channel operate?

A

simple with one one activation gate that opens once the threshold potential has reached - senses voltage difference and it opens

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16
Q

what are the two differences between Na+ and K+ voltage-gated channels?

A
  1. Na+ channels are much faster to respond to change in the membrane voltage / potential
  2. Na+ channels have in their cytosolic region an activation and an inactivation gates
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17
Q

what happens when threshold potential is reached at the channel level?

A
  • potassium and sodium gates open
  • sodium inactivation gate begins to close
  • all occurs at the same event once the threshold is reached
  • only thing that differs is how quickly these events occur
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18
Q

how fast do the gates of the sodium voltage gated channels open?

A

activation gate - very rapidly
inactivation gate - quite slow

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19
Q

how fast is the potassium’s gate to open?

A

quite slow

20
Q

what has huge implications for the shape and physiology of the action potential?

A

the rate at which the voltage gated ion channels are opening

21
Q

what is the state of the voltage gated channels at rest (-70mV)?

A
  • all voltage-gated channels are CLOSED
  • Na+ channels are in the configuration with the inactivation gate open but the activation gate closed
22
Q

the electrical and concentration gradients favour sodium movement into or out of the cell?

A

into the cell

23
Q

what leads to greater depolarization of the membrane?

A

inward movement of Na+ ions

24
Q

what leads to the positive feedback cycle?

A

opening of more voltage-gated Na+ channels because of the sodium ions being entered from the already opened voltage gated sodium ion channels

25
Q

when we have the initial depolarization, are all the voltage gated sodium channels opening?

A

no, only some

26
Q

what does the positive feedback cycle esnure?

A

that once the threshold potential is reached, all the voltage gated sodium channels will open
- this is what is responsible for the explosive increase in Na+ permeability

27
Q

there is so many voltage gated sodium ion channels that membrane permeability is how much more permeable to sodium than potassium when they are open?

A

membrane is 600 times more permeable to Na+ than to K+ when their is an active potential
- this is why there is the explosive depolarization event

28
Q

why does depolarization stop very abruptly at +30mV in action potential?

A

because of the sodium voltage channel inactivation gate

29
Q

what allows the very rapid depolarization event to occur in action potential?

A

the rate at which the sodium channels open and then inactive

30
Q

how long is the ball and chain inactivation gate of a sodium channel in a closed and incapable of opening again state for?

A

until the membrane potential is back to its resting value

31
Q

what resets your sodium ion channels?

A

bringing the membrane potential to rest

32
Q

what happens if you want to generate multiple action potentials?

A

you need to first depolarize and repolarize the cell to ensure the sodium voltage gated ion channels are capable of opening again

33
Q

what does the potassium gated ions respond to?

A

threshold potential being reached
- starts opening at the exact same time as your voltage gated sodium ion channels just occurs more slowly

34
Q

what repolarizes after a depolarization of action potential?

A

the potassium voltage gated ion channels
- this makes the inside of the cell more negative because the potassium ions are leaving

35
Q

summary of what happens/gets activated when threshold potential is reached

A
  1. rapid opening of voltage-gated Na+ channels –> Na+ influx until inactivation gate closes
  2. slow closing of the Na+ channel inactivation gates –> Peak; prevents the action potential from increasing further and exceeding +30mV
  3. slow opening of voltage-gated K+ channels (reverse polarity, returns membrane potential towards resting)
36
Q

when do the potassium voltage gates begin to fully open?

A

at peak during action potential
- permeability increased to about 300x because the outward K+ movement is down its concentration AND electrical gradient at peak

37
Q

what is responsible for the rapid repolarization of the action potential?

A

the electrical and chemical gradient pushing potassium out of the cell using all the K+ gated ion channels

38
Q

how come there is a hyperpolarization after repolarization?

A

because the potassium ion gated channels take awhile to close again

39
Q

when does an action potential only occur?

A

ONLY when the triggering stimulus AND the current that is generated via the opening of Na+ channels (graded potentials) are sufficient to reach the threshold potential

40
Q

what is threshold stimuli?

A

if the strength of your graded potentials are sufficient to reach threshold

41
Q

what is the threshold of most excitable membranes be?

A

15 mV less negative than the resting potential
- ex. resting of a neural cell is -70mV so its threshold is -55mV

42
Q

what happens if the initial depolarization is lower than the threshold?

A
  • action potential will not be activated - ONLY graded potential
  • the positive feedback cycle does not start
43
Q

what is weak depolarization that does not activate an action potential called?

A

sub-threshold potential

44
Q

what is the stimulus that does not active an action potential called?

A

sub-threshold stimulus

45
Q

what happens if the initial depolarization reaches the threshold?

A
  • an action potential is generated
  • all action potentials have similar amplitude regardless of how long it took to reach threshold (same magnitude and duration every time)
  • once the threshold is reached –> All-or-None law
46
Q

what is used for communication?

A

action potentials

47
Q

if all action potentials have the same magnitude, how do we integrate the magnitude of the stimulus? (how do we feel the different levels of touch/pain)

A

the frequency of action potentials
- the rate at which they are firing

KINE2011: Human Physiology (29 decks)

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