Lecture 06 Cardiac Muscle Tissue Flashcards Preview

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Flashcards in Lecture 06 Cardiac Muscle Tissue Deck (134):
0

What is true of cardiac muscle cells but not skeletal muscle fibers?

Cells are mononucleated

1

What are the characteristics of the cardiac muscle tissue syncytium?

Sarcomeric arrangement (striated)
Mononucleated
Central nuclei
Syncytium
Intercalated discs
Cells may branch

2

What are the changes of mV in a ventricular fiber during action potential?

Averages about 105 mV
Rises from -85 to +20mV
Remains depolarized for about .2 sec following initial spike
Plateau
Sudden repolarization at the end of the plateau

3

Where are T tubules found in skeletal muscles fibers compared to cardiac muscle fibers?

T tubules are found at the ends of the thin filaments in skeletal muscle and along the z line in cardiac muscle

4

How many T tubules per sarcomere in skeletal muscle fibers?

2

5

What do T tubules form with the sarcoplasmic reticulum in the cardiac muscle fiber?

Diads

6

What do T tubules form with the SR in skeletal muscle fiber?

Triads

7

The SR is less extensive in which type on muscle fiber?

Cardiac

8

What do cardiac muscle cells form?

Syncytium

9

In the motor unit arrangement in the skeletal muscle fiber, how many nerve fiber synapses with one or more muscle fibers?

1

10

Why does cardiac muscle fibers only form diads?

T tubules are at the very end so there is room for only one cisternae on one side of the tubules

11

What are the two main types of cardiac action potentials?

Fast and slow

12

Fast action potentials are found where?

Atria, ventricles and conduction system (purkinjie)

13

Where do the very rapidly conducting but non-contractile action potentials occur?

purkinje fibers

14

Where do the rapidly conducting and contractile action potentials occur?

Atrial and ventricular fibers

15

Where are slow cardiac action potentials found?

SA and AV nodal tissues

16

What are the characteristics of Slow cardiac action potentials?

Conduct slowly and automatically depolarizes during resting phase

17

What are the peaks of amplitude in fast and slow cardiac action potentials?

Fast 100mV
Slow 60 mV

18

What does it mean when slow cardiac action potentials automatically depolarizes during resting phase?

Start to creep back up and its automatic. Its leaky and reach threshold and fires again. Doesnt need any extrinsic signal

19

The resting potential of -85 mV is characteristic of which of the following phases of the cardiac fast action potential?

Stage 4

20

What are the phases of fast action potentials?

Phase 4: resting potential
Phase 0: Rapid depolarization
Phase 1: Initial, incomplete repolarization
Phase 2: Plateau or slow decline of membrane potential
Phase 3. Reploarization

21

Fast action potentials are due to changes in conductance of what ions?

potassium, sodium, and calcium ions

22

What is the conductance pattern mostly due to?

Voltage dependent gates

23

What results in a fast conduction velocity

Greater AP amplitude
More rapid rate of rise of phase 0
Larger cell diameter

24

Slow action potentials do not have what type of gates?

Fast sodium ion gates

25

What is the upstroke (depolarization) of action potential due to?
Slow action potential

Calcium

26

Why does Calcium proceed slowly?

Because Ca concentration is much lower outside of the cell than the sodium concentration

27

Resting phase potential 4 is close to what mV?
Slow action potential

-60mV

28

True/False
Change in slow action potential (amplitude) is less than that for fast action potentials

True

29

SA and AV nodal tissue spontaneoulsy do what to reach threshold during phase 4?

Depolarize slowly

30

What are the characteristics of fast type contractile myocytes?

Large diameter
High amplitude
Rapid onset of action potential

31

What are teh characteristics of fast type non-contractile myocytes?

Very large diameter
Very rapid upstroke

32

What are the characteristics of slow type non-contractile myocytes?

Small diameter
Low amplitude
Slow rate of depolarization

33

What channels cause the action potential in ventricular fibers?

Fast sodium channels and slow calcium-sodium channels

34

What is responsible for the initial spike of action potential in ventricular fibers

Fast sodium channels

35

What ion is necessary for electrical-mechanical coupling?

Calcium

36

What is the source of calcium necessary for electrical-mechanical coupling

T tubules via diffusion through voltage-dependent dihydrophyridine receptors
And cisternae through channels called ryanodine recpeptors

37

What type of calcium channels are found in the T tubule membrane in cardiac muscle?

L - type and they are referred to as dihydropyridine receptors and they open in response to the action potential

38

Once calcium is flowing through the dihydropyridine receptors, they cause what channel to also open and release what ion?

Open the calcium release channels in the SR and they are referred to as ryanodine receptors

39

Why is it impossible to generate another action potential during absolute refractory period?

During the period the sodium channel gates are closed and nothing will get them open

40

Why during the relative refractory period a stronger than normal stimulus can generate an action potential?

Towards the end of the repolarization this period occurs where some of the gates can now open at that point.

41

What makes a refractory period either shorter or longer?

The faster the ion channels and gates return to phase 4 stage the short the RP
The slower the ion channels and gates return to phase 4 the longer the RP

42

What is involved in gradual depolarization?

SA AV nodes and the purkinje fibers

43

Does the SA node or the AV node usually depolarizes more rapidly than the others and reaches threshold first?

SA

44

What becomes the normal "pacemaker" of the heart's rhythmicity?

SA node

45

What determines the rhythmicity of the cell?

Rate of depolarization

46

Gradual depolarization during phase 4 is cause by what?

Special sodium channels which open following phase 3

47

What is responsible for the plateau that characteries a cardiac muscle action potential?

A high concentration of calcium ions in the intracellular fluids

48

What is the difference between the repolarization in skeletal muscle vs cardia muscle?

In both the skeletal muscle and the cardiac muscle the sodium channels close rapidly, however the calcium channels open slowly and stay open for a longer period of time in cardiac muscle

49

What ions are responsible for the plateau in action potential in cardiac muscles?

Calcium ions - Channels open slowly and Ca slowly comes in
Potassium - channels open slowly
So with Ca slowly coming in and adding to the positivity and on top of that the K is not leaving quickly then it plateaus

50

In what tissue are there far fewer ca-induced calcium release channels? what does this allow?

In cardiac muscle and this allows fine control over sarcoplasmic calcium concentration and contractility.

51

Can fine control over sarcoplasmic calcium concentration and contractility happen ins skeletal muscle? why or why not?

No, excitation always triggers maximum release of calcium from the SR

52

What is the electromechanical coupling

The coupling which transforms an electrical impulse into a mechanical action

53

What are the two ways Ca is removed from the intracellular fluid?

It is sequestered into the SR using ATP.
It is pumped out of the cell using antiporters secondary transport. Sodium calcium pumps

54

The sodium-calcium exchanger in the sarcolemma of the cardiac muscle cell is an example of what mechanism?

Secondary active transport involving antiporter

55

Relaxation is the result of which two transporters?

SERCA-Sarcoplasmic reticulum calcium ATPase
Sodium-calcium exchanger in the sarcolemma

56

How does SERCA work?

Stimulated by phosphorylation via an integral SR protein called phospholambian. Reduces its ability to inhibit the SERCA pump.
Returns calcium to the SR during diastole

57

What does SERCA allow?

Even greater calcium release on the next beat and for fast clearance of calcium from the sarcoplasm

58

Left ventricular isovolumic contraction occurs immediately following what events?

Closure of AV valve

59

What is diastole?

When ventricles are relaxed

60

What is systole?

When ventricles are contracted

61

On the electrocardiogram, what does the P section represent?

Represents atrium contracting and there is depolarization of the atrial muscle

62

On the electrocardiogram what does the QRS section represent?

Represents the ventricular contraction and depolarization

63

The T curve in the electro cardiogram represents what?

The reploarization of the ventricle

64

Why is the repolarization of the atrium not represented in the electrocardiogram?

Because it is hidden by the QRS wave

65

What are the three section of diastole?

Rapid inflow: Blood into the atrium
Diastasis: Slow inflow of blood into the atrium
Atrial systole: Atrium contracts

66

Is there any electrical activity happening in Diastole?

Not until the last step of atrial systole and the atrium contracts

67

What period of diastole becomes compressed when the heart rate goes up rapidly?

The diastasis

68

When does the Ventricular volume increase?

During the Diastole when the AV valve opens and blood flows into the ventricle

69

When the AV valve closes what opens? Does this start the systole or diastole stage?

The aortic valves open and it starts the systole. The atrium has contracted and closed

70

When does the ventricular pressure and aortic pressure increase?

During the systole stage and the blood is being ejected.

71

If atrium does not contract do the ventricles still fill with blood?

Yes

72

When does the majority of blood flow from the atria to the ventricles?

80% of blood flows before the atria contract

73

How much additional blood flow does the contraction of atria contribute?

20%

74

What valves are closed during systole?

AV valves

75

When do the AV valves open? And why?

At the end of systole because of increased pressures in the atria

76

True/False
Blood is always flowing into the atriums

True

77

During what period are the ventricles contracting?

Isovolumic contraction

78

During the isovolumic periods are the valves open or closed

All where closed

79

What happens during the Isovolumic relaxtation?

Ventricles are relaxing

80

Why are AV valves closed during systole?

To keep the blood from going back into the atrium

81

What is the purpose of the chordae tendineae and papillary muscle?

To maintain proper tension and keep the flaps from going backwards on the tricuspids and mitral (this would cause blood to flow back into the atrium)

82

Which of the following statements is true for the period of rapid ejection?
a. It occurs when the left ventricular pressure is above 80mmHg.
b. The semilunar valves are closed during this phase.
c. It occurs during the last two - thirds of ejection
d. It results in the ejection of about 90% of the total volume of blood

A.

83

During diastasis a small amount of blood flows into the ventricles, what does this represent?

Blood that continues to flow into atria during diastole. Blood is continuously flowing into the atria

84

During atrial systole how much blood is pushed into the ventricles?

20%

85

What are Semilunar valves?

Half moon like crescent valves that are the pulmonary and aortic valves

86

What are the AV valves?

Mitral and tricuspid

87

What happens during the isometric contraction?

Isometric is the same as isovolumic
Ventricles contract but the semilunar valves do not open for .02 to .03 seconds

88

What does the A on artial pressure represent?

After depolarization/contraction of atria (p) the a on the atrial pressure graph rises.

A represents pressure wave caused by atrial contraction

89

What does the C represent on the atrial pressure?

Pressure wave caused by backflow of blood into atria at beginning of ventricular contraction

90

What does the V represent on the atrial pressure?

Pressure wave caused by slow flow of venous blood into atrium while AV valves are closed

91

The slow flow of venous blood into the atrium causes the pressure in the atrial pressure to increase. What does this pressure allow?

This allows for when the AV valves open for most of the blood to flow through before the atrial contraction

92

When does the period of rapid ejection occur?

Occurs when left ventricular pressure is a little above 80 mm Hg and right ventricular pressure is slightly above 8 mm Hg

93

What valves are open during rapid ejection?

Semilunar valves open

94

Why is the pressure higher during rapid ejection in the left ventricular pressure (80 mm Hg) than the right ventricular pressure (8mm Hg)?

High pressure is in the aorta vs in the low pressure in the pulmonary artery. Mechanics are the same but left has higher pressure going into the systemic system.

95

Are the volumes in each ventricle the same?

Yes - unless you are increasing heart rate then there is one cycle period necessary to readjusting the volume equilibrium between the two ventricles

96

Why is the pressure on the left side 80 mm Hg?

Has to slightly surpass the back pressure in the proximal aorta (ascending aorta) only way to force the aortic valve open

97

How much blood is ejected during the rapid ejection?

70% of the blood that will be ejected. We are not going to eject all of the blood that is in the ventricle.

98

What period of systole is there rapid ejection?

The first third of ejection

99

What is the period of slow ejection?

Remaining 30% of blood is ejected from the ventricles and occurs during the last two-thirds of ejection

100

What is the Frank-Starling Law?

The greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta

101

What does the stretching of the cardiac muscle do to actin and myosin filaments?

Brings the actin and myosin filaments to a more nearly optimal degree of overlap for force generation. So the myosin and actin are not completely pulled apart but and some overlap is there, then there is more room to create a contraction

102

Stroke volume output can be increased by which of the following mechanisms?
A. Decreasing EDV
B. Increasing EDV
C. Increasing ESV
D. By decreasing EDV and increasing ESV

B

103

What is EDV?

End Diastolic volume. Referring to the ventricle
Volume at the end of diastole - how much blood has come into the ventricle before the ventricles are going to contract
110-120 mL volume per cycle but can be increased to 180 mL

104

What is SV?

Stroke volume - The amount of blood that will be pumped out of the ventricle per cycle. 70 mL

105

If there are about 70 beats/min and 70mL of blood pumped out per beat, how much blood is pumped out of the heart per minute?
(70kg male)

5L is the average

106

What is ESV?

End systolic volume, Volume of blood in the ventricle at the end of systole. When the ventricle contracts ( no matter how strong) there will be some blood left in the ventricle. Blood left is usually 40-50mL but can be as little as 10ml

107

What is ejection fraction?

SV/EDV
% of blood that was originally in the ventricle that was ejected.
SV = 70
EDV = 110
70/110 = 64%

108

How can stroke volume output be increased to more than double?

By decreasing the amount of blood still left in the ventricle (ESV)
Increasing the amount of blood in the ventricle before contraction
Increase EDV from 110 to 180 in the ventricle before
Decrease ESV from 50 to 10 what is left
180-10 = 170 ejected
The norm was 70 SV now its 170 SV so more than doubled

109

Why would the heart increase the amount of blood per cycle?

Tissue in need of more oxygen

110

When the ventricle fills up why does the pressure not increase by much?

Because the AV valve is open which relieves some of the pressure

111

What are the phases of EW

Phase I: Period of filling
Phase II: Isovolumic contraction
Phase III: period of ejection
Pase IV: Isovolumic relaxation

112

What happens to volume and pressure during the isovolumetric contraction?

The volume remains the same (AV just shut and the aortic is shut) but the ventricle contracts so the pressure goes up

113

When isovolumetric contraction end, why does the Aortic valve opens?

The pressure is a little bit more than the back pressure in the aorta.

114

What happens to the pressure during the period of ejection?

the pressure continues to increase because the ventricle continues to contract and pushes the blood out of the ventricle. As blood leaves the ventricle the pressure in the ventricle begins to drop

115

What causes the aortic valve to close?

There is a lot of blood in the aorta now so the high pressure in the aorta, there is enough back pressure to have it close

116

What is EW?

The area that shows the net external work by left ventricle during the cardiac cycle. Shows how much work is done by the heart

117

What is the flow and velocity in the proximal aorta?

Mean velocity = 40 cm/s
Flow is phasic
Velocity 120 cm/s (systole) to negative value before aortic valves close in diastole (backflow)

118

What is phasic?

Flows up and down in concert with the pulsation of the heart itself

119

When is velocity greater in the distal aorta and arteries?

Greater in systole than diastole

120

Why does the blood continue to flow in a forward flow once it is pumped out of the heart?

The blood vessel walls during diastole are elastic and when expanded they will begin to contract down and that will cause the blood to flow foward

121

What is the rate of blood flow to each tissue controlled by?

Usually precisely controlled in relation to tissue need

122

How much more blood flow with active tissues need compared to at rest?

20 to 30 times more

123

Cardiac output cannot exceed ______ x greater than at rest

4-7

124

What monitors tissue needs?

Microvessels

125

What do the needs of tissues act directly on?

Local blood vessels

126

What else can help control tissue blood flow?

Nervous control and hormones

127

What does the parasympathetic system primarily focused on?

Controlling the heart rate, controlling the pacemakers of the heart

128

Sympathetic nervous system is primarily focused on what?

the force of contraction

129

At any given right atrial pressure, the cardiac output increases during increased _________ stimulation

Sympathetic

130

Note that at any given right atrial pressure, the cardiac output decreases during increased _______ stimulation

parasympathetic

131

Starting at what pressure does the heart start to decrease the amount of blood pumped from 5L/min?

175 arterial pressure (mm Hg)

132

Excess potassium in the extracellular fluid would have what effect on the heart activity?

Heart will become dilated. More blood is coming in that cant be pumped out. Heart becomes weaker. Harder to get an action potential because K cant leave the intracellular fluid to repolarize

133

What will an increase in the concentration of Ca in the extracellular matrix result in?

Heart rate will increase
Heart will go toward spastic contraction
Heart action potential will increase