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Physiology > Electrophysisology of the heart > Flashcards

Electrophysisology of the heart Flashcards

(85 cards)

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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
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

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