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Cardiovascular System > Electrical Activity of the Heart > Flashcards

Electrical Activity of the Heart Flashcards

1
Q

What is the membrane round the heart muscle fibres called?

A

Sarcolemma

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2
Q

What is the function of the of the sarcoplasmic reticulum?

A

It is a calcium ion store, this calcium is released during an action potential to cause contraction by binding to troponin.

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3
Q

How would you describe the cardiac muscle in terms of synchronisation?

A

It is a functional syncytium

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4
Q

In what way the the heart a functional syncytium?

A

The cells are connected electrically and physically so contract in synchrony.

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5
Q

What feature of cardiac cells allows them to be connected electrically?

A

gap junctions

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6
Q

What feature of cardiac cells allows them to be connected physically?

A

desmosomes

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7
Q

Describe the make-up of the intercalated discs in cardiac muscle?

A

Pattern of desmosome, gap junction, desmosome and so on…

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8
Q

What is the function of t-tubules?

A

Allows depolarisation of all muscle cell.

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9
Q

Is the action potential longer or shorter in cardiac muscle than with skeletal muscle?

A

longer

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10
Q

Why is the AP longer in cardiac muscle than in skeletal muscle?

A

Because in cardiac muscle Ca+ ions must also move in through form outside the cell and not only from the SR.

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11
Q

How is the strength of contraction of the heart regulated?

A

From the amount of calcium that enters from outside the cell.

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12
Q

Which cardiac cells have unstable resting membrane potentials?

A

pacemaker cells

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13
Q

What is contraction of heart muscle stimulated by?

________-______ coupling

A

Excitation-contraction

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14
Q

What is the process of a normal muscle contraction?

A

1) Action potential reaches cell and causes Na voltage channels to open.
2) Cell depolarises and causes calcium to be released from sarcoplasmic reticulum.
3) Calcium binds to troponin and starts the muscle contraction.

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15
Q

Where is actin anchored?

A

Z-line

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16
Q

What allows cardiac cells to act as one big cell?

2 points

A

Gap junctions allowing the cells to communicate to each other by using signalling molecules.

Desmosomes preventing the cells from separating during contraction.

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17
Q

What do gap junctions allow?

A

Cardiac cells to communicate with each other using signalling molecules (electrically).

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18
Q

What do desmosome junctions do?

A

Prevent cells from separating during a contraction.

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19
Q

What are intercalated disks?

A

Connect cardiac cells to allow them to work as a single functional organ.

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20
Q

What are the differences (in terms of length) between the action potentials of skeletal muscle and cardiac muscle?

A

Action potential lasts for way longer in cardiac muscle.

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21
Q

How long does the action potential last for in skeletal muscle and cardiac muscle?

A

2ms in skeletal muscle

250ms in cardiac muscle

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22
Q

What does the action potential lasting for ages in a cardiac cell allow?

A

Calcium to enter from outside the cell as well as sodium, allowing regulation of contraction.

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23
Q

With the longer action potential, there is also a _______ _________ period.

This means cardiac muscle ______ exhibit _______ _________.

A

long refractory

cannot, tetanic contraction

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24
Q

What would happen if the cardiac muscle experienced tetanus?

A

The heart would only pump out - this would not be physiologically beneficial.

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25
Q

What specifically regulates the stroke volume?

A

Ca2+ entry from outside cell.

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26
Q

Describe the graph of membrane potential in a non-pacemaker cardiac muscle cell.

A
  • Rapid initial depolarisation from RMP to above 0mV when AP fires.
  • Plateus, begins repolarising slowly.
  • Then repolarises rapidly
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27
Q

Describe the graph of membrane potential in a pacemaker cardiac muscle cell.

A
  • cell depolarises slowly until it reaches a threshold membrane potential (-40mV)
  • then depolarises rapidly to above 0mV.
  • cell then repolarises to around -60mV before slowly starting to depolarise for the process to begin again.
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28
Q

What differences are there between cardiac and skeletal muscle due to cardiac muscle having a longer refractory period?

A

Skeletal muscle contractions can add together and accumulate (tetanus) due to many action potentials being added to one another.

Cardiac muscle has to fully contract before it can be stimulated again and so they do not add onto each other (non tetanic contraction).

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29
Q

Why is the long refractory period important in cardiac muscle?

A

Heart needs to fully contract and then relax to pump blood.

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30
Q

Sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a high rate.

What is this known as?

A

tetanus

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31
Q

What do cardiac cells that have unstable resting membrane potentials act as?

A

pacemakers

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32
Q

What does having pacemakers allow a cell to do?

A

Depolarise again quicker

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33
Q

Is there a greater K+ concentration inside or outside the cell?

A

Inside

34
Q

What cause resting membrane potential in non-pacemaker cells?

A

high permeability to K+, leaky K channels

35
Q

What is the resting membrane potential (RMP) of cardiac muscle?

A

-90mV

36
Q

What is the process of non-pacemaker action potential?

4 points

A

1) Resting membrane potential (high resting permeability to K+)
2) Initial depolarisation (increase in permeability to Na+)
3) Plateau (increase in permeability to Ca2+, L-type, and decrease in permeability to K+)
4) Repolarisation (decrease in permeability to Ca2+ and increase in permeability to K+)

37
Q

What causes the initial depolarisation in non-pacemaker cells?

A

Increase in permeability to Na+

38
Q

What causes the plateau in non-pacemaker action potentials?

A

Increase in permeability to Ca2+ (L-type)

Decrease in permeability to K+

39
Q

What causes the repolarisation of non-pacemaker action potential?

A

Decrease in permeability to Ca2+

Increase the permeability to K+

40
Q

What are the 2 different kinds of calcium channels?

A

L-type

T-type

41
Q

Do L-type or T-type calcium channels let lots of calcium in?

A

L-type

L = lots

42
Q

What cause the pacemaker potential (pre-potential) in a pacemaker action potential?

3 points

A

Gradual decrease in permeability to K+

Early increase in permeability to Na+ (Pf = P funny)

Late increase in permeability to Ca2+ (T-type)

43
Q

What causes the action potential in the pacemaker action potential?

A

Increase in permeability to Ca2+ (L-type)

44
Q

What does the pacemaker action potential of the heart explain?

A

Autorhythmicity

45
Q

What allows autorhythmicity?

A

pacemaker cells

46
Q

What brings heart cells to action potential in the first place?

A

Pacemaker action potential

47
Q

Which pacemaker cells control the heart rate?

A

The ones with the fastest rate as they depolarise the rest of the cardiac cells before the others can.

48
Q

What is the pacemaker cell of the heart?

A

The one with the fastest rhythm, all cells around it take up this rhythm.

49
Q

What can electrical activity be modulated by?

A

Sympathetic and parasympathetic systems

Drugs

Temperature

Plasma K+ conc.

Plasma Ca2+ conc.

Fibrillation and heart block

50
Q

What are examples of drugs that alter the electrical activity?

A

Ca2+ channel blocker (decrease force of contraction)

Cardiac glycocides (increases force of contraction)

51
Q

What effect does Ca2+ channel blockers have on electrical activity?

A

Decreases force of contraction

52
Q

What effect does cardiac glycocides have on electrical activity?

A

Increases force of contraction

53
Q

What effect does temperature have on electrical activity?

A

Increases about 10bpm/1oC

e.g. tachcardia with fever

54
Q

What effect does hyperkalemia have on electrical activity?

A

Fibrillation and heart block as cells depolarise in an abnormal pattern.

55
Q

What effect does hypercalcemia have on electrical activity?

A

Increased heart rate and force of contraction

56
Q

What effect does hypocalcemia have on electrical activity?

A

Decreased heart rate and force of contraction

57
Q

What is fibrillation?

A

Irregular heartbeat

58
Q

What is heart block?

A

Blocking action potentials getting from the atrium to the ventricles.

59
Q

How does hypokalemia affect heart rate?

A

Causes fibrillation and heart block (not as expected, would expect repolarisation but actually causes depolarisation)

60
Q

What ensures that both atriums and both ventricles contract at the same time?

A

Special conducting system

61
Q

What does the special conducting system ensure?

A

Both atria and ventricles contract at the same time.

62
Q

Where is the sinoatrial node located?

A

Right atrium

63
Q

What is the function of the sinoatrial node?

A

It is a pacemaker and contains the fastest depolarising pacemaker cells in the heart.

64
Q

What is the rate of depolarisation of the sinoatrial node?

A

0.5m/s

65
Q

What is the annulus fibrosis and is it conducting?

A

the layer between the atria and the ventricles, it is non-conducting.

It has no gap junctions, therefore AP stops here.

66
Q

What is the atrioventricular node?

A

It is the “delay box” that slows the movement of action potential through the heart as it is slow at conducting.

67
Q

What is the conducting speed of the atrioventricular node?

A

0.5m/s

68
Q

Which structures cause contraction of the myocardium of the ventricles?

2 points

A

Bundle of his

Purkinje fibers

69
Q

Are the purkinje and bundles of His fast or slow conducting?

What is the conducting speed?

A

Fast

5m/s

70
Q

What is the process of the activation of the special conducting system?

A
  1. Pacemaker cells in sinoatrial node depolarise.
  2. This causes depolarisation of the atria.
  3. The atrioventricular node is depolarised.
  4. The bundles of His and purkinje fibres depolarise.
  5. This causes the depolarisation of the ventricular walls.
  6. Ventricular walls repolarise.
71
Q

What do purkinje fibres ensure?

A

All of the ventricle contracts at the same time.

72
Q

Why is the delay of the antrioventricular node required?

A

So the atrium can get as much blood as possible into the ventricles.

73
Q

What is the wave seen as on an electrocardiogram?

A

Summation of little action potentials in individual myocytes.

74
Q

What does the P wave correspond to?

A

Atrial depolarisation

75
Q

What does the QRS complex correspond to?

A

Ventricular depolarisation

76
Q

What does the T wave correspond to?

A

Ventricular repolarisation

77
Q

What does first degree block look like on an ECG?

A

Time between P and QRS is too long as there is impaired conduction between atria and ventricles.

78
Q

What does second degree block look like on an ECG?

A

Time between P and QRS increases until the ventricles just don’t contract and the cycle repeats.

79
Q

What does third degree block look like on an ECG?

A

There is no conduction between the atria and ventricles, there is no apparent association between P waves and QRS complex.

80
Q

What does atrial flutter look like on an ECG?

A

P wave is superimposed on T wave, HR >150bpm

81
Q

What does ventricular fibrillation look like on an ECG?

A

P wave not visible.

Cardiovascular System (37 decks)

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