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CP Exam 2 > Lecture 1: Cardiac AP > Flashcards

Lecture 1: Cardiac AP Flashcards

1
Q

What is the major cause of depolarization (phase 0) of a neural AP?

A

Increased in Na+ conductance;

Quick to open and quick to close (after a minimal delay).

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2
Q

VGCa+ channels are activated when _____________ and opens during what phases?

A

Activated when the AP is depolarized.

Opens during phase 2 for a determined amount of time, then closes, causing phase 3

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3
Q

When are K(a) channels activated?

A

When the cell depolarizes

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4
Q

When are K(b) channels activated and what is their action?

A

Activated when the cell depolarizes

Slow to close during phase 2 and remain closed for a determined amount of time, then they open to help with phase 3.

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5
Q

Which of the following maintains an excitable cell’s RMP?

A

K+ permeability;

K+ leak helps us to develop a (-) membrane potential. Na+/K+ ATPase helps to bring it back in.

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6
Q

What contributes to repolarization of an excitable cells AP?

How so?

A

Opening of K+ gates

Na+ channels inactivation gate closes, VGK+ open.

The membrane permeability to Na+ decreases and permeability to K+ rises.

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7
Q

What is the conduction of the heart?

A
  1. SA node spontaneously depolarizes
  2. Depolarization spreds over the atrial muscle: R atria–> L atria
  3. AV node- conduction station to the ventricles; causes a delay in conduction to allow the ventricles to fill with blood.
  4. Bundle of Hiss
  5. L and R bundle branches go towards the apex of the heart
  6. Purkinje fibers turn and go to the lateral walls of the ventricle; causing contraction of the ventricles to eject the blood out of the heart.
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8
Q

Which layer of the heart receives the AP first?

A

Endocardium–> epicardium

Goes from internal–> external

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9
Q

Which depolarizes first: right ventricle epicardium or the left ventricle epicardium?

A

Right ventricle epicardium

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10
Q

During conduction, which cells repolarize first?

A

The cells that depolarize last are the FIRST ones to repolarize.

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11
Q

Unlike other muscle, conduction occurs directly in between___________in the cardiac muscle.

A

Gap junctions

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12
Q

Which layer of the heart is the first to repolarize?

A

Epicardium of the heart

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13
Q

Conduction velocity is dependent on ___________.

A

Fiber size

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14
Q

______ fibers have a faster AP transmission and thus; a greater velocity.

A

LARGER

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15
Q

What is important to remember what the purkinje fibers?

A

They have a larger diameter than the myocytes surrounding them, thus, they have a faster AP than the AV/SA.

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16
Q

Which fibers of the conduction system have the greatest conduction velocity?

A

Purkinje fibers (and atrial pathways)> atrial and ventricular muscle> AV node

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17
Q

Why is there a delay in the AV conduction?

A

Allows the atria to empty the blood into the ventricles, before they contract.

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18
Q

On its own, would the AV node generate its own spontaneous AP?

A

Yes. However, it will be slower than the SA node.

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19
Q

What does the SA node and AV node (by itself) contract at?

A

SA node–> 75 bpm

AV node–> 40 bpm

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20
Q

Without the SA or AV node, will the purkinje fibers elicit an AP?

A

Yes. It will elicit an AP and cause contraction of a myocyte, more slowly though.

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21
Q

What phase of the SA node is determinant of the HR?

A

Phase 4 depolarization of the SA node.

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22
Q

Describe the SA and AV node action potential

A

SA and AV node naturally depolarize to reach threshold, without electrical stimulation.

A. Phase 4 (Pacemaker potential):

Opening of funny VGNa+ (f) channels, which open when the membrane is repolarized causes gradual depolarization until threshold is reached.

B. Phase 0:

Slow Ca2+ channels open and special K+ (b) channels close; causing a balancing act between Ca2+ in and K+ out

C. Phase 3 (Repolarization):

-Reversal of phase 0: Slow Ca2+ gates close and special K+ (b) gates open.

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23
Q

When the SA node fires, does it fire slower or faster than other regions?

A

Slower.

24
Q

How is conduction of the AV node different than the SA node?

A

Depolarization (phase 4) of the AV node is even slower.

Thus, the AV node does not ususally reach threshold until it receives a signal from the SA node.

25
Q

How is the AP of SA and AV node different from cardiac muscle?

A

There is no phase 1 or phase 2 because there are not alot of traditional VGNa+ (m) channels.

26
Q

___________ and ___________ will remain depolarized in the SA/AV node AP.

A

Bundle of Hiss

Purkinje fibers

27
Q

If the Bundle of His and Purkinje fibers are not stimulated for an extended period of time, what will happen?

A

They will begin to spontaneously depolarize.

28
Q

The rate of the bundle and purkinje fibers is _______ than that of the AV node.

A

Slower

29
Q

Describe the AP in the fast tissue/fibers.

A

Phase 4 (RMP):

High K+ (c) conductance out of the cell sustains the RMP.

Phase 0 (Depolarization):

+VGNa+ channels (m) open, causes rapid depolarization

Phase 1 (Brief repolarization):

Inactivation gates of [VGNa+ channels] close and [K+ channels (a)] open, causing a small repolarization.

Phase 2 (Plateau phase):

Slow opening of VGCa2+ channels and special VGK+ channels (b) close.

This prolongs contraction.

Phase 3 (Repolarization):

Slow VGCa2+ channels close

K+ channels (b) open

30
Q

The speed of conduction velocity is can be seen in which phase?

This is related to differences in the speeds of what?

A

Phase 0.

Increase conduction velocity= more rapid phase 0 occurs= steeper phase 0.

This is related to the differences in speeds of the VGNa+ channels or VGCa2+ channels.

31
Q

Is the conduction velocity the same throughout the heart?

A

No. The conduction velocity will differ in different regions of the heart.

[which has the highest and lowest?]

32
Q

Defective conduction velocity of the heart

A

Disruption of conduction can occur on any fiber of the heart and it can have a big impact on heart function.

33
Q

What is AV block?

A

A defect in conduction velocity due to damage of AV node.

This delays conduction

34
Q

What is an arrhythmia?

A

Damage to the purkinje fibers, which disrupts natural conduction and the contraction of ventricles.

35
Q

What is a refractory period?

A

When the electrolyte gates have not ‘reset’ sufficiently to allow a second AP to be generated.

36
Q

What are refractory periods important for?

A

to prevent arrhythmias

37
Q

Are refractory periods longer in cardiac cells or neurons?

A

Cardiac cells

38
Q

Absolute refractory period (ARP)

A

No depolarization

from -40 and up

39
Q

Relative refractory period (RRP)

A

AP can be generated but will have abnormal conduction

between -90 and -40

40
Q

Supranormal period (SNP)

A

Cell is more excitable than normal. If a signal is sent, even if it is smaller, it will cause an AP. Just not at the same conduction speed.

Phase 0 will be tipped in the direction that will not propogate the AP at the same speed.

41
Q

If stimulated during relative refractory period, will AP be weaker, stronger or not affected?

A

WEAKER

42
Q

What is the chronotropic effect?

Positive?

Negative?

A

Chronotropic effect changes the rate of depolarization of the SA node and therefore the heart rate.

Positive chronotopic effects – increase HR

Negative chronotopic effects – decrease HR

43
Q

Dromotropic effect?

Positive dromotropic effects?

Negative dromotropic effects?

A

Dromotropic effect is the speed of conduction.

Positive dromotropic effects – increase conduction velocity through the AV node, increasing HR

Negative dromotopic effects – decrease conduction velocity through the AV node, decreasing HR

44
Q

What is the inotropic effect?

A

Inotropic effect changes the STRENGTH of muscle contraction

+: increase strength of contraction (they will contract more forcefully)

45
Q

Lusitropic effect?

A

Lusitropic effect changes the rate of muscular relaxtion.

46
Q

How will parasymapthetic stimulation to the SA/AV node affect the chronotropic effect and dromotropic effect?

A

Negative chronotopic effects –Parasympathetic stimulation: ACh binds to M2 muscarinic receptors

  • Slows opening of Na (f) channels during phase 4
  • Increases efflux of K+ via K+/ACh channels, causing hyperpolarizaiton

Negative dromotopic effects – decreases conduction velocity

Parasympathetic stimulation: ACh binds to M2/ M3 receptors

  • Decreases Ca2+ influx
  • Increases K+ efflux via K+/K-ACh channels
47
Q

____________ system innervates the SA and AV node via the _______ nerve by acting on what type of receptors that bind what?

How does this happen?

A

-Parasympathetic system innervates the SA and AV node via the vagus nerve by acting on muscarinic receptors, which bind ACh.

When ACh binds, it causes a (-) GCPR response, reducing kinase activity, phosphorylation and post-translational modification of channels.

48
Q

What is the outcome of parasympathetically stimulating the SA and AV node?

A

Slows down the heart rate.

49
Q

Can the SA/AV node and myocytes also be sympathetically stimulates?

A

Yes.

They have muscarinic (B1- adrenergic receptors) that bind NE, which causes an increase in contraction.

50
Q

How will symapthetic stimulation to the SA/AV node affect the chronotropic effect and dromotropic effect?

A

Positive chronotopic effects – increased HR by β1 adrenergic receptors increase If.

Positive dromotropic effects – increase conduction velocity through the AV node increasing HR

Positive iontropic effects

51
Q

What occurs during a positive chronotropic effect?

A

+ chronotropic effect–> increase HR

  • Sympathetically stimulate the SA node.
  • NE binds to B1 adrenergic receptors, increasing rate of SA depolarization
  • Increase in opening of Na+(f) channels in Phase 4
  • Increase in Ca2+ influx
52
Q

What occurs during a positive dromotropic effect?

A

+ dromotropic effect–> increase conduction velocity–> increase HR

  • Sympathetic stimulation occurs when NE binds to B1 adrenergic receptors
  • Increase Ca2+ influx during phase 2;
53
Q

What are the effects of parasympathetic and sympathetic stimulation on phase 4 in the SA node.

A

Sympathetic- slope of phase 4 increases

Parasympathetic- slope of phase 4 decreases

54
Q

What happens if you give a patient atropine or propanolol?

A

Atropine is a muscarinic receptor antagonist- increases HR alot

Propanolol- B adrenergic antagonist- decreases HR a little.

55
Q

what is the difference between atria and ventricule AP?

A

ATria has a shoter AP than ventricles because phase 2 is not as long

CP Exam 2 (27 decks)

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