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PHYL2062 EOS > Cardiovascular L2: Electrical activity of the Heart > Flashcards

Cardiovascular L2: Electrical activity of the Heart Flashcards

1
Q

What is the flow of body from the vena cava to the body?

A
  1. Vena cava
  2. R atria
  3. R ventricle
  4. Pulmonary arteries
  5. Lungs
  6. Pulmonary veins
  7. L atrium
  8. L ventricle
  9. Body
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2
Q

Since blood flows through the heart in defined pattern, to achieve this pattern of flow, contraction of the heart must occur sequentially. What happens?

A

first the atria, then the ventricles

  • In a specific direction: atria downwards, ventricles upwards (squeeze blood to body)
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3
Q

How is the flow pattern coordinated? List 3 contributors.

A
  1. inter-connected muscle cells (talk to each other)
  2. ‘self-excitation’ (heart beats on its own)
  3. conduction system (electrical activity passes through the heart)
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4
Q

Heart walls are composed of ______ arranged cardiac muscle fibres

A

spirally

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5
Q

What are the 3 layers of the heart?

A
  1. inner layer, endothelium, lines the heart
  2. middle layer, myocardium, cardiac muscle
  3. external layer, epicardium, covers the heart
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6
Q

What is the inner layer of the heart? What is its function?

A

endothelium- lines the heart

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7
Q

What is the middle layer of the heart? What is its function?

A

myocardium- cardiac muscle (muscle cells)

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8
Q

What is the external layer of the heart? What is its function?

A

epicardium- covers the heart (sheath that holds it together)

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9
Q

What are the 5 similarities between cardiac and skeletal muscle cells?

A
  1. Striated appearance: same arrangement of thick/thin filaments
  2. Same contractile mechanism: actin, myosin, crossbridges
  3. Similar t-tubule system (although cardiac are bigger)
  4. Similar sarcoplasmic reticulum system
  5. Action potentials do not summate
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10
Q

What are 8 differences between cardiac and skeletal muscle cells?

A
  1. Contraction is involuntary Smaller cells (100 µm long)
  2. Cells connected via intercalated disks
  3. Entire heart muscle contracts in a coordinated fashion: “syncytia”
  4. SR provides 80% of calcium for muscle contraction, remainder from ECF
  5. The cardiac muscle AP lasts 200-300msecs, compared with 2-3 msecs in skeletal muscle
  6. AP propagation slower: Cardiac 0.05-0.5 m/sec vs Skeletal 3-5 m/sec
  7. AP refractory period much longer: 200-300msecs
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11
Q

Contraction is involuntary in _____ muscle cells

A

cardiac

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12
Q

Cells are bigger in cardiac or skeletal muscle?

A

skeletal

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13
Q

Cardiac muscle cells connected via ________ disks

A

intercalated

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14
Q

Entire heart muscle contracts in a coordinated fashion: “______”

A

syncytia

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15
Q

SR provides 80% of ______ for muscle contraction, remainder from ECF

A

calcium

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16
Q

What can skeletal muscles do that cardiac muscle cells can never do? List 2 things. This is a good thing or not?

A
  1. The cardiac muscle AP lasts 200-300msecs, compared with 2-3 msecs in skeletal muscle
  2. AP refractory period much longer: 200-300msecs

This means that cardiac muscle cannot summate (i.e can’t have tetanus in cardiac muscle cells) (unlike skeletal- used as a way to increase strength in muscles) due to the long AP and long refractory period This is a good thing = don’t want it in the heart

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17
Q

Cardiac muscle fibres are interconnected by ________ to form ‘functional’ syncytia

A

intercalated discs

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18
Q

What are 2 things that intercalated discs contain?

A
  1. desmesomes
  2. gap junctions
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19
Q

What are desmesomes?

A

Desmesomes holds cells together

  • Glue that holds discs together
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20
Q

What are gap junctions?

A

Gap junctions allow action potentials to spread to adjacent cells

  • Pass through from one muscle cell to the next AP spreads across all cells
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21
Q

Cardiac muscle cells all act together as one, this is called _________.

A

functional syncytia

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22
Q

The heart is ‘_________’, initiating its own rhythmic contractions

A

self-excitable

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23
Q

What are 2 things that the heart contains?

A
  1. Contractile cells, 99% of the cardiac muscle cells, who do the mechanical work
  2. Autorhythmic cells initiate the action potentials which spread across the heart (develop AP spontaneously and quickly = starts the heart beat)

Both their APs differ

24
Q

Cardiac autorhythmic cells are _________. What does this mean

A

pacemakers

  • Their membrane potential slowly depolarizes between action potentials, drifting to threshold This cyclically initiates APs that spread throughout the heart to trigger rhythmic contractions`
25
Q

Action potentials in auto-rhythmic cells are self-induced. True or false.

A

True

26
Q

What are the 4 steps of actions potentials in auto-rhythmic cells?

A
  1. Slow depolarisation Na+ permeability increases, K + permeability decreases = Na+ in
  2. Slow depolarisation (cont) Ca+ permeability increases, Na+ permeability decreases = Ca+ in
  3. Fast depolarisation transient Ca+ channels close, long-lasting Ca+ channels open = more Ca+ in
  4. Repolarisation K+ permeability increases, Ca+ permeability decreases = K+ out
27
Q

What is step 1 of actions potentials in auto-rhythmic cells?

A

Slow depolarisation Na+ permeability increases, K + permeability decreases = Na+ in

28
Q

What is step 2 of actions potentials in auto-rhythmic cells? (after Na+ comes in)

A

Slow depolarisation (cont) Ca+ permeability increases, Na+ permeability decreases = Ca+ in

29
Q

What is step 3 of actions potentials in auto-rhythmic cells? (after Ca+ comes in)

A

Fast depolarisation transient Ca+ channels close, long-lasting Ca+ channels open = more Ca+ in

30
Q

What is step 4 of actions potentials in auto-rhythmic cells? (after more Ca+ comes in)

A

Repolarisation K+ permeability increases, Ca+ permeability decreases = K+ out

31
Q

What happens to action potentials in contractile cells?

A
  • The action potential of cardiac contractile cells shows a plateau phase (allows ventricles time to contract)
  • Due primarily to activation of slow L-type Ca2+ channels
  • Ensures adequate ejection time
32
Q

Why do action potentials of cardiac contractile cells shows a plateau phase? How is done?

A
  • Ensures adequate ejection time (the delay allows contraction to take place with refractory = never summate (allow time for blood to go out = no tetanus)
  • Due primarily to activation of slow L-type Ca2+ channels
33
Q

Which 2 things prevent summation or tetanus in cardiac muscle cells?

A
  1. Plateau phase
  2. long refractory period
34
Q

What is the purpose of the cardiac conduction system?

A

To ensure that the propagation of action potentials (and therefore contraction of cardiac muscle) happens in the coordinated sequence and direction required for optimum ejection of blood (blood must leave atria before ventricles start to contract)

35
Q

What are the 3 reasons why conduction of action potentials through the heart must be coordinated?

A
  1. Atrial excitation and contraction are complete before ventricular contraction begins
  2. Excitation of cardiac muscle fibres is coordinated so each atrium and each ventricle contracts as a unit
  3. Each pair of atria and pair of ventricles needs to be coordinated so that each pair contract simultaneously
36
Q

What is the pathway of the cardiac conduction system. List the 6 structures. (the pattern of AP spread)

A
  1. Sinoatrial node (SA node)
  2. Interatrial pathyway; internodal pathway
  3. Atrioventricular node (AV node)
  4. Bundle of His (atrioventricular bundle)
  5. Purkinje fibres
  6. Spread through muscle fibre
37
Q

What is the Sinoatrial node (SA node)?

A

in right atria near opening of superior vena cava pacemaker of the heart - *pacemaker*

38
Q

What is the Atrioventricular node (AV node)

A

small bundle of cells located at base of right atrium near septum

39
Q

What is the Bundle of His (atrioventricular bundle)?

A

cells originate at AV node and enters interventricular septum

40
Q

What are the Purkinke fibres?

A

terminal fibers that extend from bundle of His and spread throughout ventricular myocardium

41
Q

What is the pathway of the cardiac conduction system. List the 5 steps (the pattern of AP spread). Be specific

A
  1. Cardiac action potential originates at the SA node
  2. AP spreads throughout right and left atria
  3. AP can only pass from atria into ventricles via AV node, does so after a brief delay (which allows atrial contraction to complete ventricular filling before ventricular contraction begins)
  4. AP travels rapidly down interventricular septum via Bundle of His, then rapidly throughout myocardium through Purkinje fibres (ventricle begins contracting from base upward)
  5. Remainder of ventricular cells activated by APs moving through gap junctions (completes ventricular contraction and ejection)
42
Q

How do you measure the electrical activity of the heart?

A

Electrocardiogram (ECG)

43
Q

How is the ECG measured?

A
  • Surface of skin
  • Safe
  • Non-invasive
  • A lot of information given
44
Q

What is the ECG?

A

The ECG is sum of the all the electrical activity as it spreads through the heart

45
Q

What does the P wave?

A

P wave represents atrial depolarization

46
Q

What is the QRS complex? What is Q? What is R? What is S?

A

QRS complex represents ventricular depolarization

Q- crossing of septum

R- coming down septum to bundle of His

S- coming up towards muscle wall

47
Q

What is T wave?

A

T wave represents ventricular repolarization

48
Q

What is the PR segment?

A

PR segment represents the AV node delay

49
Q

What does the ECG and electrical activity look like over time? What ECG trace?

A

The sum of all electrical activity.

50
Q

A ______ AP will cause a contraction.

A

Depolarising

51
Q

How does a contraction occur (mechanically and electrically)?

A
52
Q

How do we measure an ECG using limb leads?

A

Each ‘lead’ gives a different viewpoint, but with the same pattern: P,QRS,T…

  • L and R wrist and L leg
53
Q

Why is 12-lead ECG trace normal? How is this clinically relevant?

A

This is the standard

Angles = slight differences because size of waves are different.

This allows to see if there is a part of the heart that is damaged, not working properly..etc

Clinically, area of damage conduction working properly?

54
Q

ECG allows us to identify _____.

A

abnormalities

55
Q

What is a heart abnormalities in rate?

A

Tachycardia

56
Q

What are 3 heart abnormalities in rhythm?

A
  1. Extrasystole (premature ventricle contraction = extra contraction)
  2. Ventricular fibrillation (first sign which results in death)
  3. Complete heart block ( VA nodes not working)
57
Q

What is a cardiac myopathy?

A

Myocardial infarction (heart attack)

PHYL2062 EOS (13 decks)

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