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CP-1 > Cardiac Action Potentials > Flashcards

Cardiac Action Potentials Flashcards

1
Q

What is the major cause of depolarization of a neural action potential?

A

increased Na+ conductance

(voltage-gated na+ channels open rapidly –> close after minimal delay

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2
Q

What maintains resting membrane potential?

A

K+ permeability

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3
Q

For a normal AP, what is phase 4?
Phase 0?
Phase 3?

A 
4 = resting membrane
0 = depolarization
3 = repolarization
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4
Q

What is the order of how the ventricles receive an action potential?

A

endocardium before epicardium

right ventricle epicardium before left ventricle epicardium

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5
Q

What connects cardiac myocytes?

A

Gap junctions - allow Na to flow from one cell to another to spread action potentials

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6
Q

What characterizes pacemaker cells?

A

modified myocytes that can’t contract anymore
do not have true resting membrane potential
have funny Na channels that allow them to create action potential spontaneously

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7
Q

What makes the fast depolarization of cardiac myocytes occur?

A

fast sodium channels open at threshold –> action potential

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8
Q

What happens in early repolarization of cardiac myocytes?

A

K channels are open, letting some K out of cell

Ca channels are still open too though, so ca can still go in little –> membrane potential decreases only slightly

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9
Q

What happens in the plateau phase of cardiac myocytes?

A

calcium influx in cell –> calcium-induced calcium release –> muscle contraction w/ sliding filaments about halfway through the plateau
(K+ channels are still open)

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10
Q

What are the major differences in action potential of cardiac muscle and skeletal muscle?

A

Have the plateau phase in cardiac –> much longer muscle contraction
have much longer refractory period in cardiac –> so muscles fully relax and you don’t get tetany

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11
Q

What channels are open in phase 0?

A

m type Na channels = fast

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12
Q

What channels are open in phase 1?

A

m type Na channels

a type K channel = very rapid partial repolarization

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13
Q

What channels are open in phase 2?

A 
Ca channels (L type) (open slow, stay open until 3)
b type K channels (slow to close, help initiate 3)
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14
Q

What channels are open in phase 3?

A

b type K

L type Ca

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15
Q

What channels are open in phase 4?

A

c type K channels = leak, maintain resting membrane potential
f type Na channels = specific to SA and Av nodes

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16
Q

What is the function of f type Na channels and where are they found?

A

specific to SA and AV nodes

causes slow depolarization during resting phase

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17
Q

What is the conduction velocity for atrial myocytes?

A

1 m/s

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18
Q

What is the conduction velocity of the AV node?

A

0.01-0.05 m/s

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19
Q

What is the conduction velocity of a His-purkinje fiber?

A

2-4 m/s

20
Q

What is the conduction velocity of a ventricle myocyte?

A

1 m/s

21
Q

What is the parasympathetic innervation of the heart?

A

vagus n –> SA and AV nodes –> uses AcH to muscarinic receptors

22
Q

what is a chromotropic effect?

A

changes rate of depolarization of SA node –> chgs HR
+ = increased speed
- = decreased speed

23
Q

what is a dromotropic effect?

A

changes the speed of conduction

24
Q

What is an ionotropic effect?

A

changes the strength of muscular contraction

25
Q

What is a lusitropic effect?

A

changes the rate of muscular relaxation

26
Q

How does the parasympathetic NS create a negative chromotropic effect on the heart?

A

slows opening of funny Na channels in SA node

hyperpolarization by increasing K+ outward current through K+ - Ach channel

27
Q

How does the parasympathetic NS create a negative dromotropic effect on the heart?

A

decreases inward ca current
increases outward K+ current via potassium-AcH channels
–> decreases speed of conduction

28
Q

Where does the sympathetic NS innervate the heart, and through what NT and receptor?

A

SA node, AV node, and myocytes

through norepinephrine to muscarinic beta1 receptors

29
Q

What are the 3 different sympathetic effects on the heart?

A

positive chronotropic
positive dromotropic
positive ionotropic

30
Q

How does the sympathetic NS create a positive chronotropic effect on the heart?

A

increases funny Na channel opening in phase 4 of SA node

increases inward Ca current

31
Q

How does the sympathetic NS create a positive dromotropic effect?

A

increased inward Ca current during phase 2

32
Q

What is preload?

A

most accurate = amount of tension in the walls of the ventricles just before contraction is initiated
less accurate = pressure in ventricles before contraction
least accurate = volume in ventricles prior to contraction

33
Q

What is afterload?

A

amount of pressure required to eject blood from the ventricles
(a little greater than, but essentially equal to that of the aorta or pulmonary artery)

34
Q

What are inferior leads?

A

2, 3, AVF

35
Q

What are septal leads?

A

V1 and V2

36
Q

What are anterior leads?

A

V2, V3, and V4

37
Q

What are lateral leads?

A

V4, V5, V6, I, and AVL

38
Q

At what point in an EKG is the voltage difference btw ventricles the greatest?

A

T wave

39
Q

What part of the action potential does the QRS represent?

A

phase 0

40
Q

What is the diastolic pressure of the atria?

The ventricles?

A

4 mm Hg

closer to 0

41
Q

What is diastolic pressure in the pulmonary A?

The aorta?

A

15 mm Hg

80 mm Hg

42
Q

During atrial systole, why is there an increase in both atrial and ventricular pressure?

A

atria contract = increased pressure

blood flows into ventricles = increased pressure

43
Q

Why does the atrial pressure increase during ventricular systole?

A

blood is still returning to atria –> can’t glow into ventricles, so collects in atria and P goes up

44
Q

When does diastole start on the EKG?

A

at the end of the T wave

45
Q

What happens as diastole comes to an end?

A

ventricles fill up w/ blood –> flow slows down –> causes slight increase in both atrial and ventricular pressures

CP-1 (32 decks)

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