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Physiology > Electrophysisology of the heart > Flashcards

Electrophysisology of the heart Flashcards

1
Q

What are the two major types of cells in the heart? What are their jobs?

A 
myocytes (contraction)
Specialized cells (pacemakers/conduction)
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2
Q

What are myofibrils? What are they arranged into?

A

muscle cells

Arranged into a syncytium

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3
Q

What is the connection between myocytes that allows for conduction of an impulse between cells? Where are these found?

A

Gap junctions in the intercalated discs

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4
Q

Do myocytes have an intrinsic pacemaker ability?

A

No

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5
Q

Can you detect the pacemaker cells on an EKG?

A

No

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6
Q

What are the three major components of the specialized cells of the heart?

A

SA node cells
AV node cells
Purkinje fibers

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7
Q

What are syncytium? What are the two types in the heart?

A

Organized sheet of cardiac muscle cells.

There are two in the heart-atrial and ventricular

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8
Q

What is the etiology behind many cardiomyopathies?

A

Mutations in the cell membrane receptors or ion channels

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9
Q

True or false: cardiac muscle use the T tubule system

A

True

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10
Q

What are the two variable of the resting membrane potential

A

Chemical gradient

Electrical gradient

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11
Q

True or false: resting membrane potential = eqilibrum potential

A

False, equilibrium potential is different for each ion

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12
Q

What is the resting potential?

A

Resting potential for ALL ions

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13
Q

Of the ions separated by the lipid bilayer, K, Na, Cl, and Ca, which one(s) has /have a chemical gradient that is in the opposite direction than the electrical gradient?

A

K

Cl

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14
Q

Cardiac cell membranes are “only” permeable to which ion at rest?

A

K

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15
Q

What is the equation for determining the flow of ions through the membrane?

A

Ohm’s law:

I(ion) = (Vm – Veq) / R

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16
Q

The permeability of the membrane to Ca at rest is (high or low)

A

Low

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17
Q

What is the main source of Ca for cardiac muscle?

A

Extracellular

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18
Q

Is Ca needed in cardiac muscle to move the troponin off of the actin?

A

Yes (in this respect, it is more like smooth muscle)

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19
Q

What are the four types of ion channels found in cardiac muscle cells?

A

Rapid Na
Ca
K
Slow Na

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20
Q

Where are the funny channels located?

A

In the nodal cells (NOT the myocytes)

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21
Q

What is the cause of the plateau phase in cardiac myocytes?

A

Slow Ca channel opening

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22
Q

What will happen to a heart if EC Ca falls dramatically?

A

Stops beating

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23
Q

What is the resting membrane potential for myocytes?

A

-90 mV

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24
Q

What is occurring in phase 0 of the myocyte depolarization?

A

Fast Na channels open

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25
Q

What is occurring in phase 1 of the AP?

A

Early repolarization d/t closing of Na channels and a small number of K channels open

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26
Q

What happens in phase 2 of the cardiac AP?

A

Plateau phase, where Ca channels open, and K channels open

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27
Q

Why is the plateau phase needed for cardiac cells?

A

Allows ventricles to contract fully

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28
Q

What is phase 3 of the cardiac AP?

A

Repolarizaton, where Ca channels close, K channels still open

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29
Q

What is phase 4 of the cardiac AP?

A

Back to resting AP, where only K channels open

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30
Q

How long is the absolute (effective) refractory period? (ventricle and atria)

A
  1. 25 to 0.3 seconds for ventricle

0. 15 for atria

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31
Q

What determines the length of the refractory period?

A

Length of the plateau phase

B/c inactivation phase gate still closed

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32
Q

What determines the absolute refractory period? How long is it?

A

Not all ion channels are reset

0.05 seconds

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33
Q

What is the stimulus for opening of the pore region of Na channels?

A

Voltage change beyond threshold

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34
Q

What stops Na from entering the cell when the pore region is open?

A

Inactivation gate

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35
Q

What is the simulus for closing the pore region of the NA channel?

A

change in membrane potential

36
Q

What is the stimulus for inactivation of the inactivation gate?

A

time and membrane potential

37
Q

What causes atrial fibrillation?

A

A strong AP that is generated in the relative refractory period

38
Q

What are the three phases of the nodal cell’s AP?

A

2, 3, and 4

39
Q

Which of the ion channels are not present on nodal cells?

A

Fast Na channels

40
Q

What causes the depolarization in the cardiac cell’s AP (phase 2)?

A

Ca channels opening

41
Q

What is occurring (both with the AP and ion channels) in phase 3 of the nodal cell AP?

A

K channels open, depolarization

42
Q

What is occurring (both with the AP and ion channels) in phase 4 of the nodal cell AP?

A

Slow leak of Na (“funny current”) that slowly depolarizes the AP

43
Q

What is ultimately responsible for the automaticity of the nodal cells?

A

Leaky Na channels

44
Q

How does norepi work to increase the heart rate?

A

Increases Ca permeability

45
Q

How does ACh work to decrease the heart rate?

A

increases K permeability (hyperpolarizes cells)

46
Q

What is the function of the SA node?

A

Primary pacemaker

47
Q

What is the function of the AV node?

A

Secondary pacemaker

48
Q

What is the function of the purkinje fibers?

A

Rapid conduction of AP (also, tertiary pacemaker)

49
Q

What are the principal dependent and voltage dependent currents for the SA and AV node?

A

Ca, K, f

50
Q

What are the principal dependent and voltage dependent currents for the purkinje fibers?

A

Na, Ca, K, f

51
Q

What are the principal dependent and voltage dependent currents for the atrial and ventricular muscles?

A

Na, Ca, K

52
Q

What is the beta adrenergic effect on the SA node?

A

Increase conduction velocity

Increase pacemaker rate

53
Q

What is the beta adrenergic effect on the AV node?

A

Increase conduction velocity

Increase pacemaker rate

54
Q

What is the beta adrenergic effect on the ventricular muscles?

A

Increase contractility

55
Q

What is the beta adrenergic effect on the atrial muscles?

A

Increase the strength of the contraction

56
Q

What is the beta adrenergic effect on the purkinje fibers?

A

Increase the pacemaker rate

57
Q

What is the cholinergic effect on the SA node?

A

Decrease pacemaker rate

Decrease conduction velocity

58
Q

What is the cholinergic effect on the AV node?

A

Decrease pacemaker rate

Decrease conduction velocity

59
Q

What is the cholinergic effect on the atrial and ventricular muscles?

A

little effect

60
Q

What is the cholinergic effect on the purkinje fibers?

A

Decrease pacemaker rate

61
Q

What is the sequence of depolarization in the heart? (7)

A
  1. SA node
  2. Atrial syncytium
  3. AV node
  4. Septum
  5. Apex
  6. Free walls
  7. Base of left ventricle
62
Q

What allows the atria to contract at the same time?

A

Internodal tracts

63
Q

What is the rate of signal conduction of the purkinje fibers?

A

4 m /sec

64
Q

What is the rate of signal conduction of the cardiac myocytes?

A

0.3 - 0.5 m/sec

65
Q

What is the HR set by the SA node?

A

60-100 bpm

66
Q

What is the resting potential of the pacemaker cells?

A

-60 mV

67
Q

What is the main function of the AC node?How does it achieve this?

A

Delays the conduction of the AP, through decreased gap junctions

68
Q

What is the pacemaker rate at the AV node?

A

40 bpm

69
Q

What is the next structure that the AP travels through after the AV node?

A

Purkinje fibers, then LBB and RBB

70
Q

WHich has more branches, the LBB or RBB?

A

LBB

71
Q

What are the branches of the LBB?

A

Septal
Left anterior fascicle
Left posterior fascicle

72
Q

What is the main function of the purkinje fibers?

A

Speed signal from the septum down to the apex and out to the free walls

73
Q

What determines which part of the heart sets the pace?

A

Whichever is faster to depolarize

74
Q

What are the two causes of ectopic pacemakers?

A

Super excitable cells

Blocks

75
Q

What are the five steps of excitation coupling?

A
  1. AP down T tuble
  2. Ca release from SR
  3. Contraction
  4. Reuptake of Ca into SR
  5. Ca is exchanged with Na at the sarcolemma
76
Q

What is the channel that allows the Ca to enter the cell from the SR?

A

Ryanodine receptors

77
Q

How does the duration of the AP set the duration of the contraction?

A

Changes the amount of time Ca is available to bind to troponin

78
Q

What is the effect of a decrease in excess K?

A

slows HR
Dilates heart
Can potentially block AV bundle

79
Q

What is the effect of excess Ca on the heart?

A

Increases contraction through the direct initiation of cardiac contractile apparatus

80
Q

What is the effect of a decrease of Ca on the heart?

A

Causes a decrease in the contractile potential of the heart

81
Q

How does ACh decrease the rate of sinus node discharge?

A

Increases K permeability

82
Q

How does norepi increase the rate of sinus node discharge?

A

Changes Na and Ca permeability

83
Q

What is the effect of a K channel blocker on the heart?

A

Increases the duration of the AP; lengthens QT interval

84
Q

What is the effect of a Ca channel blocker on the heart (like verapamil)?

A

Slows rate of conduction at SA and AV by delaying Ca entry

85
Q

What is the effect of a Na channel blocker on the heart (like lidocaine)?

A

Reduce phase 0 and slope of depolarization

Physiology (75 decks)

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