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Physio Test 2 > Garman- CV2: Electrical > Flashcards

Garman- CV2: Electrical Flashcards

1
Q

What are 2 types of cell types of the heart?

A

Contractile cells and conductile cells

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2
Q

What are the contractile cells?

A

Bulk of atrial and ventricular tissues

-Work horses of heart

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3
Q

What are the conductile cells

A

Specialized cardiomyocytes
- sole puprose is to generate and propagate electrical activity across contractile cells

Found in:

  • SA node
  • Atrial internodal tracts
  • AV node
  • Bundle of His
  • Bundle branhces (L and R)
  • Purkinje Fibers
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4
Q

What are some characteristics of cardiomyocytes?

A

-sTRIATED
-50-100 uM long; diameter ~20 uM (shorter and thinner than skeletal muscle cells)
- Branched at its ends
Very small
-Mono/bi-nucleated centrally located (skeletal muscles multi-nucleated and peripherally located nuclei)
- Reduced SR system but extensive T tubule system
-Large/numerous mitochondria

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5
Q

What are intercalated disks?

A

Consist of desmosomes- mechanical coupling, gap junctions- electrical coupling

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6
Q

What is purpose of desmosomes?

A

Make sure cardiomyocytes do not tear apart at opposing plasma membranes. Keeps cells tightly bound together

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7
Q

What innervates cardiac muscle?

A

Autonomic nervous system (Brain tells heart to increase or decrease rate, or increase contractility)

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8
Q

What is source of Ca for cell?

A

SR and ECF

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9
Q

What causes removal of Ca in cardiomyocte?

A

Ca ATPase pumps (membrane and SR) AND Na/Ca exchanger (3Na/1 Ca)

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10
Q

When do atria contract to “top off” filling of ventricles?

A

End diastole

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11
Q

When are AV valves open and semilunar valves closed?

A

Passive diastole

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12
Q

When are all 4 valves closed?

A

Isovolumetric contraction and relaxation

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13
Q

When are semilunar valves open?

A

Systole

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14
Q

How long does propagation of signal to AV node take?

A

50 mseconds

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15
Q

What is the delay at AV node?

A

100 msec, total time 150 mseconds

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16
Q

How long does impulse take down bundle branch and purkinje fibers via moderator band?

A

175 msec elapsed time

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17
Q

How long does the impulse take to go throughout ventricular myocardium and begin contraction?

A

225 msec

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18
Q

What is normal spontaneous firing for SA node?

A

100 /min

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19
Q

What is the atrial internodal pathway?

A
  • Specialized conducting cells ~50 msec
  • Stimulus passed to contractile cells which spread it across both atria
  • Stops at atria- myocardium of atria is not connected with ventricle
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20
Q

What makes up AV node:

A
  • Smaller cells/ slows signal

- 100 msec to move through AV node

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21
Q

What is normal firing of AV node?

A

~40/min

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22
Q

What is overdrive supression?

A

Faster firing of SA node supresses other cells from acting as a pacemaker

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23
Q

What is the only electrical connection between atria and ventricle?

A

AV bundle or bundle of His

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24
Q

Which bundle branch is bigger?

A

Left

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25
Q

What are the purkinje fibers?

A
  • larger cells
  • fast conduction system
  • move upward from apex to base to push blood upward
  • Normal firing frequency 15-20/min
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26
Q

What ions are responsible for depolarization of SA node cells?

A

“funny” current for Na (trickle of Na INTO the cells) causes small upslope at baseline
- Calcium is main ion that flows into cell causing quick depolarization

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27
Q

What ion is mainly responsible for depolarization in ventricular myocytes?

A

Na

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28
Q

What is RMP of SA node cell?

A

-65 mV

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29
Q

What is RMP of ventricular myocytes?

A

-75/-80 mV

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30
Q

What is relative speed of conduction through heart?

A

Fast from SA to atria, slow through AV node, fast down purkinje fibers.

“Fast, slow, fast”

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31
Q

Do ventricular myocytes fire multiple action potentials at one time like skeletal muscle?

A

No, one and done so that heart can relax and refill in diastole

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32
Q

What happens in phase 0 of contractile cell?

A

Depolarization

  • Quick opening of VG Na channel
  • Na influx
  • T-type VGCC open- minor Ca influx (Transient-type channels)
  • Closing of K channels (inward rectifiers only)
  • Voltage gated K not open yet
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33
Q

What are the inward rectifier K channels?

A

These channels CLOSE whenever cell is depolarized. This stops K from flowing out of cell and allows action potential to occur.

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34
Q

What happens during phase 1 of AP of contractile cell?

A

Early repolarization

  • Na channels close
  • T-type VGCC close
  • K efflux through transient outward channels
  • L-type VGCC not fully open yet
  • Na/Ca reversal
  • Small repolarization caused by positive charge leaving cell via K efflux and Na/Ca reversal
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35
Q

What is Na/Ca reversal?

A
  • These utilize the Na/Ca exchanger which normally brings 3 Na+ into cell and 1 (2+) Ca out of cell.
  • These channels are always open
  • During depolarization, based on [Na], [Ca], and membrane potential, these channels SWITCH the movement of ions
  • During reversal, 3 Na pumped OUT of cell with 1 Ca (2+ charge) pumped in
36
Q

What happens during phase 2 of contractile cell AP?

A
  • L-type VGCC OPEN!!
  • Calcium influx (this regulates height of plateau)
  • K channels (Ks and Kr) partially open, some K efflux
  • Vm near reversal potential of Na/Ca exchanger
37
Q

What happens during phase 3 of contractile cell AP?

A
  • L type VGCC cloase
  • K (Ks, Kr, and Ki) all fully open
  • efflux in K causing rapid repolarization (inward rectifier open causing K to rush out)
  • Influc of Na and efflux of Ca through Na/Ca exchanger
38
Q

How does absolute refractory period of heart compare to skeletal muscle?

A
  • Much longer absolute refractory period in cardiac muscle compared to nerve/skeletal muscle
  • Limits frequency of AP
  • This allows a built-in safety mechanism and prevents tetanic contractions and ectopic pacemakers from stimulating contraction
39
Q

Longer absolute refractory period allows ventricle to ____

A

Fill

40
Q

How long is the absolute refractory period in heart muscle?

A

200 msec

41
Q

How does Ca activate excitation-contraction coupling in cardiomyocyte?

A
  • Ca enters cell through L-type Ca Channels
  • This Ca binds to ryanodine receptors on SR and stimulates release of Ca from SR

causes Calcium induced calcium release

42
Q

How are the L-type Ca channel and ryanodine receptors different in cardiac muscle?

A

They are not connected.

43
Q

How is Ca removed in cardiomyocyte?

A
  • Ca pumped back into SR via SERCA pump (Ca-atp pump into SR)
  • Ca also extruded to ECF with Na/Ca exchanger
44
Q

Are all L-type channels the same in the body?

A

No, L-type in cardiac myocytes do not connect to ryanodine receptors, therefore meds can just target cardiac muscle (i.e. CCB)

45
Q

What happens during phase 4 of cardiomyocyte action potential (contractile cell)

A

Diastole

  • K (Ki) channels remain open- near nernst potential
  • All other channels are closed
46
Q

What happens during phase 4 of SA node AP?

A

Pacemaker potential

  • Na channels open- funny current (influx)
  • Voltage gated K channels closed– upward drift of membrane potential from funny currents
  • T-type VGCC opens mid-phase
  • Slow influx of Ca, slow depolarization
47
Q

What happens during phase 0 of SA node AP?

A

Depolarization

  • T-type VGCC closes
  • L types VGCC opens
  • Large influx of Ca and rapid depolarization
48
Q

What happens in phase 3 of SA node AP?

A

Repolarization

  • L type VGCC closes
  • Influx of Ca stops
  • VG K channels open
  • Efflux of K
49
Q

Are there phase 1 or 2 in SA node?

A

No

50
Q

What is ECF concentration Na?

A

140 mEq/L

51
Q

What is ICF concentration Na?

A

14 mEq/L

52
Q

What is ECF concentration K?

A

4.5 mEq/L

53
Q

What is ICF concentration K?

A

120 mEq/L

54
Q

What is ECF concentration Ca?

A

2.5 mEq/L

55
Q

What is ICF concentration Ca?

A

0.0001 mEq/L

56
Q

How does sympathetic regulation (Beta 1 receptors/Norepi) influence HR?

A
  • Positive chronotropic effect from increased firing rate of SA node
  • This stimulation causes opening of Na and Ca ion channels, causing influx of Na and Ca and increases the steepness of pacemaker potential
  • Cell has reduced repolarizaiton, and is therefore able to meet threshold for AP quicker causing increased HR
57
Q

How does parasympathetic regulation affect heart rate?

A
  • Negative chronotropic effect form decreasing firing rate of SA node/HR

Muscarinic/Ach receptors cause opening of K channels (via increased conductance for K)

  • This causes efflux of K
  • This hyperpolarizes cell and decreases steepness of pacemaker potential, taking MORE time to reach threshold causing AP
58
Q

What is ERP in ventricular myocytes?

A

Effective refractory period- the time frame where another AP cannot be elicited

59
Q

What is the RRP in ventricular myocyte?

A

Relative refractory period- more difficult to elicit and AP than during phase 4

60
Q

What causes a noticeable spike on EKG?

A
  • More mass, “noiser”= bigger spike

- In uniform, more noticeable (uniform P wave in SR vs no uniform p wave in afib)

61
Q

What does P wave represent? Normal duration?

A

Atrial depolarization

0.08-0.10 sec

62
Q

What does QRS complex represent? Normal duration?

A

Ventricular depolarization

0.06-0.10 sec

63
Q

What does T wave represent?

A

Ventricular repolarization

no normal

64
Q

What does PR interval represent? Normal duration

A

Atrial depolarization plus AV nodal delay

0.12-0.20 sec

65
Q

What does ST segment represent?

A

Isoelectric period of depolarized ventricles

66
Q

What does QT interval represent? Normal duration?

A

Length of depolarization plus repolarization- corresponds to A.P. duration
0.20-0.40

67
Q

What does lead I resemble?

A

RA–> LA

68
Q

What does lead II represent?

A

RA–> LL

69
Q

What does lead III represent?

A

LA–> LL

70
Q

What does aVr represnt?

A

Looking up toward right hand form center

71
Q

What does aVL represent?

A

Looking up at left hand from center

72
Q

What does aVF represent?

A

Looking down to LL from center

73
Q

When current flows toward red arrowheads (on limb lead drawing), ______ deflection occurs in EKG.

A

Upward

74
Q

When current flows away from red arrowheads, ______ deflection is seen in EKG.

A

Downward

75
Q

When current flows perpendicular ot red arrows _____ deflection or biphasic deflection occurs.

A

No

76
Q

When impulse orginates at SA node, a wave of depolarization spreads over atria, resulting in electrical vector directed ________ and to left. This causes an ______ deflection in ECG in tracing I and aVF

A

Downward; upward (positive)

77
Q

After delay in AV node, impulse traverses common bundle of His and R/L BB and inters interventricular septum, causing myocardial depolarization with electrical vector directed to right and downward. This results in small _______ deflection in lead I and ______ deflection in lead aVF.

A

Negative (downward)= Q wave lead I

Positive (upward)= R wave in AVF

78
Q

During apical and early ventricular depolarization, impulse continues along conduction system, causing depolarization of apical ventricular myocardium with electrical vector directed downward and to left. This results in large _________ deflection in lead I and extends R wave in lead AVF

A

Positive (upward)

79
Q

During late ventricular depolarization, depolarization spread over ventricles and vector shifts to become directed superiorly and to the left, thus ______ Rwave in lead I and causing ______ deflection in avf

A

Extending; negative (downward)= S wave in avf

80
Q

Whean heart is fully depolarized, there is no electrical activity for a preif period (ST segment). Then repolarization begins from epicardium to endocardium, producing electrical vector directed downard and to left causing _______ deflection in lead I and AVF..

A

Upward (positive)= T wAVE

81
Q

Baseline on EKG means ____

A

No electrical activity occuring

82
Q

Overall direction of vector during atrial depolarization?

A

Down and to left

83
Q

Overall direction of vector in septal depolarization

A

Down and to right

84
Q

Overall direction of vector in apical and early left ventricular depolarization

A

Down and to left

85
Q

Overall direction of late ventricular depolarization vector?

A

Up at to left

86
Q

Overall direction of repolarization vector?

A

Slight down and to left

Physio Test 2 (10 decks)

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