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ICPP 2023 > Action Potential > Flashcards

Action Potential Flashcards

(43 cards)

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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?

Study These Flashcards
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?

Study These Flashcards
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?

Study These Flashcards
A

Closure of V gated K+ channels

21
Q

What triggers an action potential?

Study These Flashcards
A

Depolarisation to threshold at axon hillock

22
Q

What does depolarisation to threshold trigger?

Study These Flashcards
A

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

23
Q

What does depolarisation trigger?

Study These Flashcards
A

Inactivation of V gated Na+ channels

Voltage gated K+ channels open

24
Q

Is the Na+K+ATPase involved in repolarisation?

Study These Flashcards
A

NOOOOOOOOO (just sets up gradients)

25
What is absolute refractory period (ARP)?
Na+ channels are inactivated Depolarisation cannot re-occur no matter stimulus No other action potential can occur during this
26
What is relative refractory period?
Na+ channels are closed (not inactivated) If stimulus is strong, can cause opening of channels and depolarisation V gated K+ channels are closing
27
structure of V gated Na+ channel
1 alpha subunit four similar sections voltage sensor (in S4) pore region (P)
28
what is important about the S4 voltage sensor?
Contains positively charged amino acid residues senses changes conformational change
29
What is located between 3rd and 4th sections of alpha subunit on Na+ channel?
Inactivation particle Enters pore when membrane is depolarised Inactivates channel so no Na+ can enter
30
structure of v gated K+ channels
4 individual a subunits voltage sensor (s4) Pore region NO INACTIVATION
31
What does pore region contribute to?
Selectibility - only tries to allow K+ ions through
32
differences V gated K+ channel and V gated Na+ channel
No inactivation in K+ channel | K+ is made of 4 subunits, Na+ only 1
33
Phases of V gated Na+ channel
Closed, Open, Inactivated
34
What form of anesthetic is permeable to the membrane?
Unprotonated | hydrophobic/lipophilic
35
example of anaesthetic
Lidocaine
36
How does lidocaine work?
``` Hydrophilic pathway (open channel block) Hydrophobic pathway (inactivated) ``` (block Na+ channels)
37
Hydrophilic/open channel pathway
``` Channel must be open Drug crosses membrane (uncharged hydrophobic) Gets protonated inside cell Enters Na+ channel Blocks ```
38
Hydrophobic pathway
Drug crosses membrane (uncharged hydrophobic) Moves into Na+ channel within membrane (across) Gets protonated Blocks Na+ channel STRONGEST
39
When is block in strongest form?
When the Na+ channel is in inactivated state
40
How is unblocking occur?
Channel must be closed | Drug gets deprotonated
41
Local anaethetics blocking order
small myelinated axons unmyelinated axons large myelinated axons
42
why is important Na+ channels become inactivated?
So action potentials occur in one direction
43
What is the consequence of delayed closing of V gated K+ channels?
Membrane gets hyperpolarised | Na+ channels can be reactivated

ICPP 2023 (31 decks)

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