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<3 > Cardiac Action Potential And Conduction > Flashcards

Cardiac Action Potential And Conduction Flashcards

1
Q

What is the order of action potential spread in the heart?

A 
SA node 
—> AV node
—> bundle of His 
—> R/L bundle branches
—> purkinje fibers
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2
Q

What will conduct its action potential first,

RA or LA?

A

RA

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3
Q

What will conduct its action potential first,

Endocardium or Epicardium?

A

Endocardium

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4
Q

What will conduct its action potential first,

RV epicardium or LV epicardium?

A

RV epicardium

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5
Q

Is the conduction velocity of the SA node or AV node faster?

A

SA node ( 1 m/s)

Vs AV = 0.01-0.05 m/s

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6
Q

What generates an action potential most frequently in the heart?

A

SA node

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7
Q

What is overdrive suppression?

A

The order in which things will “become” the pacemaker

-SA node then AV node then Purkinje

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8
Q

What determines how fast a cell fiber will be?

How would you order purkinje, atrial & ventricle muscle, and AV node fibers?

A

Cells w/ fibers of larger diameter = faster

Purkinje > Atrial & ventricular muscle > AV node

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9
Q

What are the cardiac cells that have pacemaker potential?

A

Sa nodal cells

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10
Q

What will voltage gated sodium channels open?

Abbreviation?

A

Open during phase 0 and 1

Ina

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11
Q

What will potassium current open?

Abbreviation?

A

Open during phase 1

Ito

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12
Q

What will L-type Ca channel oepn?

A

Open during phase 2 and 3

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13
Q

When will the K Chanel open and close?

A

Clsoed = 2 and 3

Open = helps w/ phase 3

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14
Q

When are the Rpaid and SLow K channels open?

A

During phase 3

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15
Q

What is the K+ leak channels open ?

A

Open always

-during phase 2 they would have an increased current outward

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16
Q

What is the Na channel open and closed?

A

Closed = 4

Open = 3 (during repolarization to help slow depolarization from RMP)

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17
Q

What occurs during Fast Phase 0 ?

A

In ventricular and atrial myocytes

  • voltage gated Na channels open
  • transient outward (Ito) potassium current is going out of cell
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18
Q

What occurs during Fast Phase 1?

A

Initial repolarization in ventricular and atrial myocytes

  • Voltage gated Na channels = closed
  • voltage gated K channels = open and leaving
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19
Q

What occurs during fast phase 2?

A

Plateau phase in Ventricular and Atrial Myocytes

  • L-type Ca channels = oepn and Ca enters
  • voltage gated K = oepn and K leaving

Ca entering/K leaving counters charges and stabilizes membrane potential

20
Q

What occurs during fast phase 3?

A

Repolarization in ventricular and atrial myocytes

Ca channels = closed
Voltage gated K = open
Rapid and slow K = open

21
Q

What occurs during Fast PHase 4?

A

RMP in ventricular and atrial myocytes

Voltage gated Na, K, Ca = closed

Cell is at normal resting potential = -70–90 mV

22
Q

What is the inward rectifier current (Ik1)?

A

Closed during phase 0 (Depolarization)

Helps to stop some of the outward K current to help maintain phase 2 (plateau phase)

Open during phase 3 (to help w/ repolarization)

23
Q

What occurs in Slow Phase 4?

A

RMP in SA and AV nodes

Funny Na channel = open

24
Q

What determines how fast HR will be?

A

How fast the funny sodium channels open

25
Q

What occurs in slow Phase 0?

A

Depolarization in sa and Av noes

-Ca channels = oepn
Ca coming in and is larger than sodium
—> influx is slower and depolarization takes a longer time

26
Q

What occurs in Slow phase 3?

A

Repolarization in Sa and AV nodes

  • voltage gated K = open
  • Ca channels = closed
27
Q

Why is the SA node the pacemaker?

A

Bc it has intrinsic, spontaneous depolarization ability via Funny, voltage gated Na channels that open upon complete repolarization of membrane

28
Q

Why is there a “fast” and “slow” phase?

A

Bc the slow phase uses Ca in depolarization which is bigger than sodium

—> influx is slower
—> slower to depolarize

(Fast uses Na)

29
Q

What are refractory periods?

A

Periods when AP cannot be generated or are generally more difficult to generate

30
Q

Why are refractory periods longer in cardiac cells?

A

Help to prevent arrhythmias

31
Q

What is an Absolute Refractory Period (ARP)?

A

When no AP can be generated bc voltage gated K channels are closed and unable to open

32
Q

What is a Relative REfractory Period (RRP)?

A

AP can be generated but requires greater stimulus and/or have abnormal conduction

33
Q

What is a Supranormal period (SNP)?

A

cell is more excitable than normal and easier to general AP

May have abnormal conduction

(Has not fully repolarized yet)

34
Q

What will happen if the cardiac cells are stimulated during RRP or SNP?

A

Conduction of AP wil be weaker

35
Q

What does a Chronotropic effect do?

A

Changes HR

Slope of depolarization in Phase 4- RMP - at SA node, the funny sodium channels!

36
Q

What does a Dromotropic effect do?

A

Effects speed of conduction

Slope of phase 0 - depolarization

37
Q

What does an Inotropic effect do?

A

Affects strength of muscular contraction

CHANGES STROKE VOLUME

38
Q

What does a Lusitropic effect do?

A

Affects rate of muscular relaxation

39
Q

What effect will Parasympathetic stimulus have on the the AP?

A

negative chonotropic effect (lower HR)

Negative dromotropic effect (lower conduction velocity)

40
Q

What is the N., NTR and R. Of Parasympathetic stimulus to the heart?

A

CN 10 —> SA and AV nodes

NTR: ACTH

R: Muscarinic (M2/M3)

41
Q

How does parasympathetic stimulus affect Chronotropy? (2 ways)

A
  1. Slower opening of funny Na channels during phase 4
    —> takes longer for SA node to reach threshold
    —> slower HR
  2. =hypo-polarization of SA node by incr. outward K current via special K channels
42
Q

How does parasympathetic stimulus affect Dromotropy? (2 ways)

A
  1. Reduced inward Ca current
  2. Increased K+ outward current via special K+ channels

= slower speed of conduction

43
Q

What does sympathetic stimulus affect chrontropy and dromotropy?

A

Positive chronotropic effects = increased HR

Positive Dromotropic effects = increases Conduction velocity

44
Q

Where does Sympathetic stimulus go in the heart?

What is the NTR and r.?

A

To SA and AV nodes and ventricular myocytes

NTR: NE

R: Beta-1 Adrenergic

45
Q

How does sympathetic stimulus cause a positive chronotropic effect?

A

Increases HR by…

  1. More rapid opening of funny Na channels during phase 4
46
Q

How does sympathetic stimulus cause positive dromotropic effects?

A

Will increase speed of conduction by…

  1. Increased inward Ca++ current
47
Q

What are the actions of sympathetic and parasympathetic stimulation on HR?

A

Sympathetic

  1. Hypo-polarize
  2. Increased inward Na

Parasympathetic

  1. Hyper-polarize
  2. Decreased inward Na

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