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Drew 921 > Cardiac Electrophysiology > Flashcards

Cardiac Electrophysiology Flashcards

1
Q

What channels are responsible for phase 0 of the cardiac action potential?

A

v.g. Na+ channels

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2
Q

What channels are responsible for phase 1?

A

1) K+ (i_to)

2) Cl-

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3
Q

What channels are responsible for phase 2?

A

1) L-type Ca++ (i_Ca)
2) K+ (i_to)
3) activation of K+ (i_kr)

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4
Q

What channels are responsible for phase 3?

A

1) K+ (i_Kr)

2) K+ (i_K1)

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5
Q

What channels are responsible for phase 4?

A

K+ (i_K1)

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6
Q

What occurs in phase 0?

A

rapid upshoot

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7
Q

what occurs in phase 1?

A

early repolarization

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8
Q

what occurs in phase 2?

A

plateau (ERP)

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9
Q

what occurs in phase 3?

A

repolarization

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10
Q

what occurs in phase 4?

A

resting membrane potential

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11
Q

What are intercalated disks?

A

irregular, transverse thickenings of the sarcolemma between muscle cells

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12
Q

What structures make up an intercalated disk?

A

desmosomes

gap junctions

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13
Q

what is a functional syncytium vs. a true syncytium?

A

functional syncytium: group of cells that WORK like a long, multi-nucleated cell but is not actually one

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14
Q

what is a desmosome?

A

spot weld

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15
Q

What are K+ i_to channels responsible for?

A

phase 1, but active until after phase 2

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16
Q

What are K+ i_Kr channels responsible for?

A

phase 3, with slow activation in phase 2

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17
Q

What are K+ i_K1 channels responsible for?

A

Phases 3 & 4

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18
Q

What are K+ i_KAch1 channels responsible for?

A

parasympathetic nervous system input

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19
Q

how do K+ i_Kach1 channels work?

A

activated by ACh & G-protein coupled

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20
Q

Describe the gating of cardiac sodium channels?

A

1) m-activation: -65mV, 0.1msec

2) h-activation: +30mV, 1msec; remains closed until partial repolarization in phase 3

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21
Q

What are the types of cardiac calcium channels?

A

1) L-type

2) T-type

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22
Q

Describe the L-type cardiac calcium channel’s contribution to the cardiac action potential.

A

1) activated at -10mV
2) responsible for Ca influx during phase 2
3) slow inactivation
L = long lasting, predominant in heart (CCB targets)

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23
Q

Describe a t-type calcium channel.

A

t = transient

less abundant in heart

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24
Q

Describe contraction of a cardiac myocyte?

A

1) sarcolemma depolarized, Ca++ opens @ -10mV
2) cytosol Ca++ binds SR receptor
3) Calcium-induced Calcium-release
4) SR releases calcium –> sarcomere –> contraction

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25
Q

Describe relaxation of a cardiac myocyte

A

1) Ca++ sequestered in SR (SERCA ATPase)
2) Ca++ sequestered in ECF
- - Na/Ca exchanger uses gradient from Na/K ATPase

26
Q

Why does extracellular [Ca] affect contraction?

A

SR does not store enough Ca for strong contraction

T-tubules are large to allow Ca entrance

27
Q

How does excess K+ affect cardiac function?

A

1) more positive RMP
2) more excitable myocyte with slower depol, faster repol
3) less Ca++ influx = decreased contractility

28
Q

What is the target of cardiac glycosides?

A

Na/K ATPase

29
Q

What is a cardiac glycoside?

A

Digitalis (digoxin)

30
Q

How do cardiac glycosides work?

A

Na/K ATPase inhibited

 - - accumulation of intracellular Na+
 - - Na/Ca++ exchanger inhibitied
 - - increased concentration of intracellular Ca++
 - - increased contractility, decreased HR
31
Q

Where is the SA node located?

A

in RA below superior vena cava

32
Q

How does a pacemaker function?

A

Leaky Na+ and Ca++ channels –> spontaneous phase 4 depol

33
Q

What is the RMP of a pacemaker cell?

A

-55 to -60 mV

34
Q

What is the threshold of a pacemaker cell?

A

-40mV

35
Q

RMP of cardiac myocyte?

A

-75 mV

36
Q

Where is the AV node located?

A

base of right atrium

37
Q

How is the AV nodal delay achieved?

A

1) smaller fibers (smaller d, slower contraction)
2) fewer gap jxs
3) more negative RMP
4) slower Ca++ channels

38
Q

Describe the AV bundle.

A

large, fast fibers in myocardial septum continuous with purkinje fibers

39
Q

Describe the relative conduction velocity of the AV bundle compared to myocyte & AV node fibers.

A

6x myocyte conduction

150x AV Node fiber conduction

40
Q

What are the intrinsic pacemaking cells of the heart?

A

all cells!

41
Q

What is the normal pacemaking rate of the SA node?

A

100/min

42
Q

What is the normal pacemaking rate of the AV node?

A

40-60/min

43
Q

What is the normal pacemaking rate of the purkinje fibers?

A

15-40/min

44
Q

What is the normal pacemaking rate of a ventricular myocyte?

A

5-10/min

45
Q

Define ectopic pacemaker.

A

another part of the heart with rhythmic discharge rate > that of SA Node

46
Q

Consequences of ectopic pacemaker?

A

circus rhythms

47
Q

Where are the usual places for ectopic pacemakers?

A

AV node or Purkinje

48
Q

Define chronotropism.

A

change in HR

49
Q

Define dromotropism

A

Change in AV Nodal conduction

50
Q

What is a positive dromotropism?

A

decreased AV delay

51
Q

What is a positive chronotropism?

A

tachycardia

52
Q

What does the PNS innervate to affect HR?

A

vagus nerve innervates SA & AV node

53
Q

How does the PNS affect HR?

A

ACh opens K+ channels for hyperpolarization & longer time till threshold

54
Q

What does the SNS innervate to affect HR?

A

SA for HR,

ventricles for contractility

55
Q

How does the SNS affect HR?

A

NE opens Ca++ channels for depolarization

56
Q

What is the thin filament?

A

actin

57
Q

What is the thick filament?

A

myosin

58
Q

What does TnC do?

A

binds Ca++ to induce conformational change

59
Q

What does TnT do?

A

binds tropomyosin

60
Q

What does TnI do?

A

binds actin

61
Q

What is tropomyosin?

A

the filament protein regulating exposure of actin’s active site

Drew 921 (33 decks)

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