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ICPP 2023 > Action Potential > Flashcards

Action Potential Flashcards

1
Q

What is an action potential?

A

Change in voltage across a membrane

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2
Q

What does an action potential depend on?

A

Ionic gradients and relative permeability of the membrane to different ions

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3
Q

An action potential only occurs when…

A

…a threshold voltage level is reached

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4
Q

Action potential in axon values:
1) Length
2) RMP
3) Depolarisation peak

A

1) 0.5ms
2) RMP = -70mV
3) Depolarisation peak = +30mV

Depolarisation peak: +30mV

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5
Q

Action potential skeletal muscle values:
1) Length
2) RMP
3) Depolarisation peak

A

1) 0.5ms
2) RMP = -90mV
3) Depolarisation peak = +40mV

Depolarisation peak: +40mV

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6
Q

Sino-atrial node action potential values:
1) Length
2) RMP
3) Depolarisation peak

A

1) 100ms
2) RMP = -60mV
3) Depolarisation peak = +30mV

Depolarisation peak: +30mV

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7
Q

Cardiac ventricle action potential values:
1) Length
2) RMP
3) Depolarisation peak

A

1) 100ms
2) RMP= -90mV
3) Depolarisation Peak = +30mV

Depolarisation peak: +30

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8
Q

How long does action potential last in axon/skeletal muscle?

A

0.5ms

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9
Q

How long does action potential last in SA node/cardiac ventricle?

A

100ms

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10
Q

What does the conductance (g) of a membrane to an ion dependent on?

How do you increase the conductance of sodium?

A
  • The number of channels for that ion that are open
  • E.g. to increase the conductance of sodium, you need to increase the number of open sodium channels in the membrane

higher conductance = more channels open

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11
Q

What happens to the membrane potenital if you increase conductance of any ion?

A

Membrane potential moves towards the equilibrium potential for that ion

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12
Q

What amount of ions need to move to produce a relatively large change in the membrane potential?

How does axon diameter affect this?

A
  • A very small amount of ions
  • The larger the axon diameter, the smaller the amount of ions required to move to produce a large change in MP
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13
Q

Membrane potential during action potential

A 
V gated Na+ channels open 
Na+ channels inactivate
V gated K+ channels open
Hyperpolarisation  
Na+ channels become reactivated but remain closed 
V gated K+ channels close
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14
Q

What occurs when V gated channels of Na+ open?

A

Membrane gets depolarised as Na+ enters cells

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15
Q

How are V gated Na+ channels reactivated?

A

After membrane gets hyperpolarised

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16
Q

How can we show experimentally that Na+ is responsible for AP depolarisation?

A

If you decrease extracellular Na+, peak of action potentials get smaller

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17
Q

How can membrane currents be measured over time at a set membrane potential?

A

Voltage clamp

K+ causes hyperpolarisation, Na+ causes depolarisation

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18
Q

How does conductance change over action potential?

A

Na+ channels conductance changes rapidly - quickly inactivate in response to depolarisation
K+ channels are slower at closing so have a shallower curve

19
Q

How does hyperpolarisation occur?

A

Non voltage gated K+ channels are naturally open

When you pair this with open v gated k+ channels membrane gets more negative than RMP

20
Q

What causes membrane to go back RMP after hyperpolarisation?

A

Closure of V gated K+ channels

21
Q

What triggers an action potential?

A

Depolarisation to threshold at axon hillock

22
Q

What does depolarisation to threshold trigger?

A

Positive feedback to open Na+ channels and allow influx of Na+

23
Q

What does depolarisation trigger?

A

Inactivation of V gated Na+ channels

Voltage gated K+ channels open

24
Q

Is the Na+K+ATPase involved in repolarisation?

A

NOOOOOOOOO (just sets up gradients)

25
Q

What is absolute refractory period (ARP)?

A

Na+ channels are inactivated
Depolarisation cannot re-occur no matter stimulus
No other action potential can occur during this

26
Q

What is relative refractory period?

A

Na+ channels are closed (not inactivated)
If stimulus is strong, can cause opening of channels and depolarisation
V gated K+ channels are closing

27
Q

structure of V gated Na+ channel

A

1 alpha subunit
four similar sections
voltage sensor (in S4)
pore region (P)

28
Q

what is important about the S4 voltage sensor?

A

Contains positively charged amino acid residues
senses changes
conformational change

29
Q

What is located between 3rd and 4th sections of alpha subunit on Na+ channel?

A

Inactivation particle
Enters pore when membrane is depolarised
Inactivates channel so no Na+ can enter

30
Q

structure of v gated K+ channels

A

4 individual a subunits
voltage sensor (s4)
Pore region
NO INACTIVATION

31
Q

What does pore region contribute to?

A

Selectibility - only tries to allow K+ ions through

32
Q

differences V gated K+ channel and V gated Na+ channel

A

No inactivation in K+ channel

K+ is made of 4 subunits, Na+ only 1

33
Q

Phases of V gated Na+ channel

A

Closed, Open, Inactivated

34
Q

What form of anesthetic is permeable to the membrane?

A

Unprotonated

hydrophobic/lipophilic

35
Q

example of anaesthetic

A

Lidocaine

36
Q

How does lidocaine work?

A 
Hydrophilic pathway (open channel block)
Hydrophobic pathway (inactivated)

(block Na+ channels)

37
Q

Hydrophilic/open channel pathway

A 
Channel must be open
Drug crosses membrane (uncharged hydrophobic)
Gets protonated inside cell
Enters Na+ channel
Blocks
38
Q

Hydrophobic pathway

A

Drug crosses membrane (uncharged hydrophobic)
Moves into Na+ channel within membrane (across)
Gets protonated
Blocks Na+ channel
STRONGEST

39
Q

When is block in strongest form?

A

When the Na+ channel is in inactivated state

40
Q

How is unblocking occur?

A

Channel must be closed

Drug gets deprotonated

41
Q

Local anaethetics blocking order

A

small myelinated axons
unmyelinated axons
large myelinated axons

42
Q

why is important Na+ channels become inactivated?

A

So action potentials occur in one direction

43
Q

What is the consequence of delayed closing of V gated K+ channels?

A

Membrane gets hyperpolarised

Na+ channels can be reactivated

ICPP 2023 (31 decks)

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