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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
Describe relaxation of a cardiac myocyte
1) Ca++ sequestered in SR (SERCA ATPase) 2) Ca++ sequestered in ECF - - Na/Ca exchanger uses gradient from Na/K ATPase
26
Why does extracellular [Ca] affect contraction?
SR does not store enough Ca for strong contraction | T-tubules are large to allow Ca entrance
27
How does excess K+ affect cardiac function?
1) more positive RMP 2) more excitable myocyte with slower depol, faster repol 3) less Ca++ influx = decreased contractility
28
What is the target of cardiac glycosides?
Na/K ATPase
29
What is a cardiac glycoside?
Digitalis (digoxin)
30
How do cardiac glycosides work?
Na/K ATPase inhibited - - accumulation of intracellular Na+ - - Na/Ca++ exchanger inhibitied - - increased concentration of intracellular Ca++ - - increased contractility, decreased HR
31
Where is the SA node located?
in RA below superior vena cava
32
How does a pacemaker function?
Leaky Na+ and Ca++ channels --> spontaneous phase 4 depol
33
What is the RMP of a pacemaker cell?
-55 to -60 mV
34
What is the threshold of a pacemaker cell?
-40mV
35
RMP of cardiac myocyte?
-75 mV
36
Where is the AV node located?
base of right atrium
37
How is the AV nodal delay achieved?
1) smaller fibers (smaller d, slower contraction) 2) fewer gap jxs 3) more negative RMP 4) slower Ca++ channels
38
Describe the AV bundle.
large, fast fibers in myocardial septum continuous with purkinje fibers
39
Describe the relative conduction velocity of the AV bundle compared to myocyte & AV node fibers.
6x myocyte conduction | 150x AV Node fiber conduction
40
What are the intrinsic pacemaking cells of the heart?
all cells!
41
What is the normal pacemaking rate of the SA node?
100/min
42
What is the normal pacemaking rate of the AV node?
40-60/min
43
What is the normal pacemaking rate of the purkinje fibers?
15-40/min
44
What is the normal pacemaking rate of a ventricular myocyte?
5-10/min
45
Define ectopic pacemaker.
another part of the heart with rhythmic discharge rate > that of SA Node
46
Consequences of ectopic pacemaker?
circus rhythms
47
Where are the usual places for ectopic pacemakers?
AV node or Purkinje
48
Define chronotropism.
change in HR
49
Define dromotropism
Change in AV Nodal conduction
50
What is a positive dromotropism?
decreased AV delay
51
What is a positive chronotropism?
tachycardia
52
What does the PNS innervate to affect HR?
vagus nerve innervates SA & AV node
53
How does the PNS affect HR?
ACh opens K+ channels for hyperpolarization & longer time till threshold
54
What does the SNS innervate to affect HR?
SA for HR, | ventricles for contractility
55
How does the SNS affect HR?
NE opens Ca++ channels for depolarization
56
What is the thin filament?
actin
57
What is the thick filament?
myosin
58
What does TnC do?
binds Ca++ to induce conformational change
59
What does TnT do?
binds tropomyosin
60
What does TnI do?
binds actin
61
What is tropomyosin?
the filament protein regulating exposure of actin's active site

Drew 921 (33 decks)

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