Electrophysisology of the heart Flashcards Preview

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Flashcards in Electrophysisology of the heart Deck (85):
1

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

myocytes (contraction)
Specialized cells (pacemakers/conduction)

2

What are myofibrils? What are they arranged into?

muscle cells

Arranged into a syncytium

3

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

Gap junctions in the intercalated discs

4

Do myocytes have an intrinsic pacemaker ability?

No

5

Can you detect the pacemaker cells on an EKG?

No

6

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

SA node cells
AV node cells
Purkinje fibers

7

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

Organized sheet of cardiac muscle cells.

There are two in the heart-atrial and ventricular

8

What is the etiology behind many cardiomyopathies?

Mutations in the cell membrane receptors or ion channels

9

True or false: cardiac muscle use the T tubule system

True

10

What are the two variable of the resting membrane potential

Chemical gradient
Electrical gradient

11

True or false: resting membrane potential = eqilibrum potential

False, equilibrium potential is different for each ion

12

What is the resting potential?

Resting potential for ALL ions

13

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?

K
Cl

14

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

K

15

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

Ohm's law:

I(ion) = (Vm – Veq) / R

16

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

Low

17

What is the main source of Ca for cardiac muscle?

Extracellular

18

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

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

19

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

Rapid Na
Ca
K
Slow Na

20

Where are the funny channels located?

In the nodal cells (NOT the myocytes)

21

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

Slow Ca channel opening

22

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

Stops beating

23

What is the resting membrane potential for myocytes?

-90 mV

24

What is occurring in phase 0 of the myocyte depolarization?

Fast Na channels open

25

What is occurring in phase 1 of the AP?

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

26

What happens in phase 2 of the cardiac AP?

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

27

Why is the plateau phase needed for cardiac cells?

Allows ventricles to contract fully

28

What is phase 3 of the cardiac AP?

Repolarizaton, where Ca channels close, K channels still open

29

What is phase 4 of the cardiac AP?

Back to resting AP, where only K channels open

30

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

0.25 to 0.3 seconds for ventricle

0.15 for atria

31

What determines the length of the refractory period?

Length of the plateau phase

B/c inactivation phase gate still closed

32

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

Not all ion channels are reset

0.05 seconds

33

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

Voltage change beyond threshold

34

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

Inactivation gate

35

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

change in membrane potential

36

What is the stimulus for inactivation of the inactivation gate?

time and membrane potential

37

What causes atrial fibrillation?

A strong AP that is generated in the relative refractory period

38

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

2, 3, and 4

39

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

Fast Na channels

40

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

Ca channels opening

41

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

K channels open, depolarization

42

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

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

43

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

Leaky Na channels

44

How does norepi work to increase the heart rate?

Increases Ca permeability

45

How does ACh work to decrease the heart rate?

increases K permeability (hyperpolarizes cells)

46

What is the function of the SA node?

Primary pacemaker

47

What is the function of the AV node?

Secondary pacemaker

48

What is the function of the purkinje fibers?

Rapid conduction of AP (also, tertiary pacemaker)

49

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

Ca, K, f

50

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

Na, Ca, K, f

51

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

Na, Ca, K

52

What is the beta adrenergic effect on the SA node?

Increase conduction velocity
Increase pacemaker rate

53

What is the beta adrenergic effect on the AV node?

Increase conduction velocity
Increase pacemaker rate

54

What is the beta adrenergic effect on the ventricular muscles?

Increase contractility

55

What is the beta adrenergic effect on the atrial muscles?

Increase the strength of the contraction

56

What is the beta adrenergic effect on the purkinje fibers?

Increase the pacemaker rate

57

What is the cholinergic effect on the SA node?

Decrease pacemaker rate
Decrease conduction velocity

58

What is the cholinergic effect on the AV node?

Decrease pacemaker rate
Decrease conduction velocity

59

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

little effect

60

What is the cholinergic effect on the purkinje fibers?

Decrease pacemaker rate

61

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

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

62

What allows the atria to contract at the same time?

Internodal tracts

63

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

4 m /sec

64

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

0.3 - 0.5 m/sec

65

What is the HR set by the SA node?

60-100 bpm

66

What is the resting potential of the pacemaker cells?

-60 mV

67

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

Delays the conduction of the AP, through decreased gap junctions

68

What is the pacemaker rate at the AV node?

40 bpm

69

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

Purkinje fibers, then LBB and RBB

70

WHich has more branches, the LBB or RBB?

LBB

71

What are the branches of the LBB?

Septal
Left anterior fascicle
Left posterior fascicle

72

What is the main function of the purkinje fibers?

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

73

What determines which part of the heart sets the pace?

Whichever is faster to depolarize

74

What are the two causes of ectopic pacemakers?

Super excitable cells
Blocks

75

What are the five steps of excitation coupling?

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

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

Ryanodine receptors

77

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

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

78

What is the effect of a decrease in excess K?

slows HR
Dilates heart
Can potentially block AV bundle

79

What is the effect of excess Ca on the heart?

Increases contraction through the direct initiation of cardiac contractile apparatus

80

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

Causes a decrease in the contractile potential of the heart

81

How does ACh decrease the rate of sinus node discharge?

Increases K permeability

82

How does norepi increase the rate of sinus node discharge?

Changes Na and Ca permeability

83

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

Increases the duration of the AP; lengthens QT interval

84

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

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

85

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

Reduce phase 0 and slope of depolarization