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Cardio/Pulm Final > Lecture 4: Cardiac Action Potential > Flashcards

Lecture 4: Cardiac Action Potential Flashcards

1
Q

What is the Na+ (f) gate specific for and when is it activated?

A
  • Funny voltage-gated Na+ channels
  • Specific to SA and AV node where it causes slow depolarization during resting phase
  • Activated when the SA or AV node repolarizes
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2
Q

What is the Eq. Pot. for Na+?

A

+30 mV

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3
Q

What is the Eq. Pot for K+?

A

-90 mV

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4
Q

What is the Eq. Pot. for Ca2+?

A

+40 mV

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5
Q

During what phase are the Na+ (f) gates open?

A

Phase 4 (SA or AV node repolarization)

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6
Q

What constitutes phase 0 of AP for ventricles, atria, and purkinje system?

A

Rapid upstoke (depolarization) caused by crossing threshold (RMP) and voltage-gated Na+ channels opening

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7
Q

What constitutes phase 1 of AP for ventricles, atria, and purkinje system?

A

Small repolarization caused by start of the Na+ (m) gates closing and some K+ (a) gates opening

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8
Q

Function of the K+ (a) channels opening during phase 1?

A

Cause a very rapid partial repolarization

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9
Q

What occurs during phase 2 of AP for ventricles, atria, and purkinje system; what is this phase referred to as?

A
  • Plateau phase
  • Sustained by slow Ca2+ channels opening and closing of special, voltage gated K+ (b) channels
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10
Q

Function of the Ca2+ channels opening in phase 2?

A

Cause a slow inward current of Ca2+ to go along with the outward current of K+. Membrane potential remains at a stable depolarization (plateau)

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11
Q

Other than helping to stabilize membrane potential during phase 2, what is another important function of Ca2+ influx?

A

Causes the release of more Ca2+ from intracellular stores for excitation-contraction coupling.

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12
Q

What occurs during phase 3 of AP for ventricles, atria, and purkinje system?

A

Complete repolarization is caused by slow Ca2+ channels closing and K+ channels opening

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13
Q

What are the 3 characteristics of the AP in ventricles, atria, and the purkinje system?

A

1) Stable resting potentials
2) Rapid upstroke
3) Long duration

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14
Q

The resting potential (phase 4) is sustained by the high conductance of?

A

K+ (c) - the K+ leak channel

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15
Q

How does the phase 4 of AV node differ from that of the SA node?

A

Slower depolarization during phase 4, typically doesn’t reach threshold until it receives a triggering signal from the SA node.

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16
Q

What is special about the Na+ (f) channels?

A

Causes the slow, intrinsic and spontaneous depolarization of the SA and AV nodes. This “automaticity” is why the SA node is known as the pacemaker.

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17
Q

What occurs during phase 0 in the SA/AV node?

A

Depolarization due to: opening of slow Ca2+ channels and closing of special K+ (b) channels

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18
Q

Why is there no phase 1 and phase 2 in SA/AV node?

A

Due to scarcity of traditional, voltage-gated Na+ (m) channels

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19
Q

What occurs during phase 3 in the SA/AV node?

A

Repolarization due to: closing of Ca2+ gates and opening of special K+ (b) gates

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20
Q

If phase 4 of the AV node fires before that of the SA node what happens to the heart rate?

A

The rate will be much slower

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21
Q

What are considered the latent pacemakers?

A

AV node, bundle of His, and Purkinje fibers

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22
Q

What occurs to bundle of His and purkinje fibers if not stimulated for an extended period?

A

Will begin to spontaneously depolarize during phase 4

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23
Q

How does the rate of the bundle of Purkinje fibers compare to that of the AV node?

A

Slower

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24
Q

The SA node will naturally depolarize to reach threshold without?

A

Electrical stimulation

25
Q

The higher the inward current (Na+ (m)) or faster the Ca2+ current, does what for conduction velocity?

A

Higher the velocity

26
Q

How does fiber size dictate the conduction velocity?

A

Larger the fiber = faster transmission of AP = faster the velocity

27
Q

Where is the conduction velocity the greatest?

A

Purkinje (and atrial pathways): 2-4 m/s

28
Q

Where is conduction velocity the slowest?

A

AV node: 0.01-0.05 m/s

29
Q

What is the conduction velocity in the atria and ventricles?

A

1 m/s

30
Q

What is the importance of the slow conduction velocity of the AV node?

A

Allows the atria to fully contract, and for the ventricles to receive the maximum amount of blood before contraction.

31
Q

What is the refractory period?

A

The electrolyte gates have not ‘reset’ sufficiently to allow a second AP to be generated

32
Q

What is the refractory period important for in cardiac muscle?

A

To help prevent arrhythmias

33
Q

How does the refractory period in cardiac cells compare to that of neurons?

A

Longer in cardiac cells

34
Q

What is the absolute refractory period (ARP)?

A

No matter how large the stimulus is, there can be no AP generated

35
Q

What is the relative refractory period (RRP)?

A

An AP can be generated, but will required a stimulus that is greater than normal

36
Q

What is a supranormal period (SNP)?

A

When the cell is more excitable than normal, a smaller stimulus than normal can generate an AP

37
Q

If an AP is generated during the RRP, how will it compare to a normal AP?

A

Will be weaker, have an abnormal configuration, and a shortened plateau phase

38
Q

What are chronotropic effects?

A

The effects of the Autonomic Nervous System on HR

39
Q

How do chronotropic effects act on the heart?

A

Change rate of depolarization of SA node and therefore heart rate (HR)

40
Q

What are dromotropic effects?

A

The effects of the Autonomic Nervous System on conduction velocity

41
Q

Stimulation by what part of the autonomic nervous system causes positive chronotropic effects; affect on HR?

A

Sympathetic nervous system; increases HR

42
Q

Stimulation by what part of the autonomic nervous system causes negative chronotropic effects; affect on HR?

A

Parasympathetic nervous system; decreases HR

43
Q

What NT is released by the parasympathetic nervous system and what does it bind to in the SA node?

A

Releases ACh, which binds to muscarinic receptors

44
Q

How does the parasympathetic nervous system act on phase 4 in SA and AV nodes?

A

Decreases opening of special Na+ (f) gates

45
Q

How does the parasympathetic nervous systems affect on phase 4 impact the heart?

A
  • Decreased depolarization rate - Decreased HR (- chronotropy)
46
Q

What does the effect of the parasympathetic nervous system do to conduction velocity through the AV node?

A

Decrease conduction velocity

47
Q

Which parts of the heart are impacted by the parasympathetic nervous system?

A

AV nodes, SA nodes, and to a significant extent contractile myocytes

48
Q

What NT is released by the sympathetic nervous system and what does it bind to in the SA node?

A

Norepinephrine, which binds to Beta-1 receptors

49
Q

How does the parasympathetic nervous system act on phase 4?

A

Increases the opening of special Na+ (f) gates

50
Q

How does the sympathetic nervous systems affect on phase 4 impact the heart?

A
  • Increases the rate of depolarization - Increase HR (+ chronotropy)
51
Q

What does the effect of the sympathetic nervous system do to conduction velocity through the AV node?

A

Increased conduction velocity

52
Q

What is a PVC?

A

Premature ventricular heartbeat - development of new pacemaker signal (focus) in the ventricles

53
Q

What is a PAV?

A

Premature atrial heartbeat - can be from development of new pacemaker signal (focus) in atrium away from SA node (e.g., left atrium)

54
Q

What are effects of ectopic pacemakers?

A

Can cause arrhythmias, such as atrial fibrillation

55
Q

A reduction in the amount of Ca2+ entering the cell does what to myocytes?

A

Slow things down.

56
Q

What does this image depict?

A

Action potential through the Ventricle

57
Q

What does this image depict?

A

Action potential through the Atrium

58
Q

What does this image depict?

A

Action potential through the SA node

Cardio/Pulm Final (18 decks)

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