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Physiology Part 1 > Lec 6 Cardiac Cellular Electrophysiology > Flashcards

Lec 6 Cardiac Cellular Electrophysiology Flashcards

1
Q

Difference in phase 0 between SA and ventricular AP?

A

Much faster in ventricle [300 V/s vs 20 V/s]

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2
Q

Difference in phase 1 between SA and ventricular AP?

A

absent in SA AP

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3
Q

Difference in phase 2 between SA and ventricular AP?

A

abbreviated in SA

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4
Q

Difference in phase 3 between SA and ventricular AP?

A

comparable

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5
Q

Difference in phase 4 between SA and ventricular AP?

A
  • flatter, more negative in ventricle

- increasing [not flat] in SA

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6
Q

Sequence of cardiac electrical activation [6 things]

A
  1. SA node
  2. Atrium
  3. AV node
  4. bundle of His/bundle branches
  5. purkinje fibers
  6. ventricles
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7
Q

What AP is similar to SA node AP?

A

AV node AP

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8
Q

What AP is similar to ventricular AP?

A

purkinje

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9
Q

What AP is similar to atria AP?

A

none

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10
Q

How does conduction speed change in different regions [where is it noticeabley slow/fast]?

A
  • slow through AV node

- fast through his/purkinje

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11
Q

How does voltage change in depolarization?

A

Goes from -85 mV up to 0

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12
Q

How does voltage change in repolarization?

A

Goes down back to -85 mV

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13
Q

What does phase 0 represent in ventricular AP?

A

Na coming in

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14
Q

What does phase 1 represent in ventricular AP? [lease important to remember]

A
  • Na coming in and K out [K dominates]

- short burst of repolarization

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15
Q

What does phase 2 represent in ventricular AP?

A
  • Ca coming in and K out

- balance out but K winning slightly so flat [gradual repolarization]

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16
Q

What does phase 3 represent in ventricular AP?

A
  • K+ out

- strong repolarization

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17
Q

What does phase 4 represent in ventricular AP?

A
  • K out dominates, a little NCX in
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18
Q

Do SA node cells need stimulus to get AP?

A

NO!

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19
Q

Do ventricular cells need stimulus to get AP?

A

Yes

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20
Q

What is absolute refractory period [ARP]?

A

Period during action potential when its impossible to trigger a second AP

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21
Q

What is relative refractory period [RRP]?

A

Period just after action potential when you need stronger stimulus to get a weak AP

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22
Q

What does phase 0 represent in SA AP?

A

Ca influx [strong depolarization]

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23
Q

What does phase 2 represent in SA AP?

A

Ca in and K out [K very much dominates]

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24
Q

What does phase 3 represent in SA AP?

A

K out

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25
Q

What does phase 4 represent in SA AP?

A

NCX and I[f] in

26
Q

What is definition of negative current?

A

positive charge flowing inward

27
Q

What type of current is positive charge flowing out?

A

positive current

28
Q

What is driving force?

A

V-Ex where V is voltage and Ex is the equilibrium voltage for that ion

29
Q

What happens to ion if V=Ex? What type of current?

A

Ion does not move in or out of cell? No current!

30
Q

What happens to ion if [V-Ex] > 0? What type of current?

A
  • Ion moves out of cell

- positive current

31
Q

What happens to ion if [V-Ex] < 0? What type of current?

A
  • ion moves into cell

- negative current

32
Q

At what voltages is K current positive?

A

Above -90 mV

33
Q

At what voltages is Na current positive?

A

above +70 mV

34
Q

At what voltages is Na current positive?

A

above +130 mV

35
Q

At what voltages is Na current negative?

A

below + 70 mV

36
Q

At what voltages is Ca current negative?

A

below +130 mV

37
Q

At what voltages is K current negative?

A

below -90 mV

38
Q

At what voltages does Na channel open?

A

at voltage > -60 mV

39
Q

How does Na current stop? Why?

A
  • Na channel automatically closes after opening

- Opens then get current and approaches nernst equilibrium so have less driving force so current stops

40
Q

How fast does Na channel open and close?

A

4 ms

41
Q

How does Ap initiation feedback in I[NA]

A
  • as you increase V [with V still below -40 mV] you get more Ina
  • with more current you get more positive V which provides more feedback
  • inward Na current depolarizes the membrane
42
Q

At what voltage does L-type Ca channels open?

A

-40 mV

43
Q

Does Na or L-type Ca open at a higher [less negative] voltage?

A

L-type Ca [thats why Na opens first]

44
Q

How long does it take for L-type Ca channel to open and close?

A

50 ms

45
Q

Does Na or L-type Ca channel open/close faster?

A

Na 10x faster

46
Q

2 mains differences Na and Ltype Ca current?

A
  1. Ca opens at higher [more positive] voltage

2. Ca opens and inactivates slower

47
Q

What role do L-type Ca channels play in ventricular myocytes?

A
  • action potential plateau [phase 2]

- initiate SR Ca release

48
Q

What role do L-type Ca channels play in vSA and AV nodal myocytes?

A
  • action potential upstroke [phase 0]
49
Q

What role do L-type Ca channels play in vascular smooth muscle?

A
  • supply Ca for constraction
50
Q

2 types of drugs that are Ca channel blockers

A
  • type IV anti-arrhythmics

- antihypertensives

51
Q

Inwardly-rectifying K channels [Ik1] - at what voltages are they open?

A
  • open at -90 mV

- closes during action potential plateau [at higher voltages]

52
Q

What is function of Ik1 in ventricular myocytes?

A
  • stabilizes resting potential in ventricular myocytes

- keeps voltage at -85 mV

53
Q

Delayed rectifying K channels - at what voltages are they open? function in ventricular myocytes?

A
  • closed at resting potential
  • open with delay during plateau of AP
  • two type: rapid [Ikr] and slow [Iks]
  • repolarize membrane at end of AP plateau
54
Q

How do three K types act in ventricular AP?

A
  • at begining of AP: Ik1 shuts off to allow plateau

- later: Ikr and Iks open and repolarize membrane

55
Q

Why does SA node have slow depolarization rather than flat phase 4 [2 channels involved]?

A
  • inward current through NCX [3 NA in, 1 Ca out]

- inward current through “funny current”

56
Q

What is funny current I[f] in SA node?

A
  • mix of Na and K but mostly Na
  • inward current in negative voltages, it is a depolarizing force
  • closed at positive voltages [during depolarization]
57
Q

What 3 things does funny current oppose

A
  • normal Na current
  • normal Ca current
  • delayed rectifier K current
58
Q

Are Na channels present in SA and AV nodes? Where else are they present [2 places]

A
  • No not present in SA/AV

- present in: ventricles, purkinje

59
Q

What 2 channels explain why SA nodes get spontaneous APs [automaticity] and ventricular do not?

A
  • funny current present in SA not ventricle [open at negative potentials
  • Inward rectifier [Ik1] present in ventricle not SA [if it were present in SA would prevent spontaneous depolarization since maintains resting potential]
60
Q

How does phase 0 differ in ventricular and SA?

A
  • Na and Ca in ventricle
  • only Ca [no Na] in Sa
  • Na more abundant and open faster so get much faster depolarization in ventricle compared to SA
61
Q

How does phase 3 differ in ventricle and SA?

A

Its comparable

both have lots of delayed rectifier K channels

62
Q

How does phase 4 differ in ventricle and SA?

A
  • ventricle has Ik1 so stays at -85 mV so flat

- presence I[f] and absence I[k1] in SA so get slow depolarization

Physiology Part 1 (37 decks)

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