Origin of the heartbeat Flashcards

1
Q

The heart muscle is composed of two major cell types - what are these?

A
  • contractile cells (majority of heart cells) = straited
  • non-contractile cells with unstable membrane potentials (autorhythmic cells) = aid in electrical conduction
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2
Q

Membranes of non contractile cells depolarises slowly until it reaches a threshold value to generate what?

A
  • generates an action potential
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3
Q

Once an action potential has been generated (after slow depolarisation of non-contractile cell membranes) what happens to the action potential?

A
  • Action potential spreads through cellular gap junctions causing contraction of contractile cells
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4
Q

Where is the primary pacemaker region?

A
  • the sinoatrial node (SA node)
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5
Q

The SA node has the fastest rate of depolarisation why?

A
  • sets pace of heart
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6
Q

Pacemaker activity can be regulated by what?

A
  • can be regulated by autonomic NS
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7
Q

What does the heart not need to contract?

A
  • doesn’t need nerves to contract as it has an intrinsic contraction
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8
Q

What is the cardiac skeleton?

A
  • fibrous connective tissue NOT bone
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9
Q

What does the cardiac skeleton provide?

A
  • provides rigidity and site of attachment for musculature and values
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10
Q

The cardiac skeleton electrically insulates each chamber meaning it needs what for AP propagation?

A
  • wiring for AP propagation
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11
Q

What is the wiring for the AP propagation?

A
  • the conduction system
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12
Q

The SA node spontaneously depolarises - resting heart rate does what between species?

A
  • varies
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13
Q

Autorhythmic cells form a specialised conduction system what does this system allow for?

A
  • faster conduction than possible through gap junctions
  • introduce an important delay from atria to ventricles
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14
Q

List the order of conduction through the heart?

A
  1. SA node
  2. Atrial muscle
  3. AV node
  4. Bundle of HIS
  5. Purkinje fibres
  6. Ventricular muscle
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15
Q

The membrane of the SA node is what?

A
  • unstable
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16
Q

How does the SA function as a pacemaker - describe what happens within the node?

A
  • gradual and slow depolarisation of the membrane potential
  • reaches threshold potential triggers rapid depolarisation (action potential)
  • action potential in SA node terminated
  • gradual depolarisation and drift back towards threshold potential
  • these repeated slow depolarisations are called pacemaker potentials
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17
Q

Describe the pattern of a membrane potential (this would be shown on a graph):

A
  • Gradual depolarisation (becomes more positive)
  • peak of depolarisation and termination
  • repolarisation (becomes more negative)
  • starts again
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18
Q

Cell membranes keep ions at different concentrations internally vs externally.
A difference in charge across the membrane does what to it?

A
  • polarizes it
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19
Q

Most animal cells have a stable … what resting membrane potential?

A
  • a stable negative resting membrane
    = inside is negative compared to the outside
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20
Q

If ions were allowed they would diffuse .. their concentration gradient

A
  • if ions were allowed they would diffuse down a concentration gradient
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21
Q

if more ions were diffusing in then out of a cell what would happen?

A
  • depolarisation
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22
Q

If more ions were diffusing out a cell than in what would happen?

A
  • repolarisation
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23
Q

What would sodium moving into the membrane do?

A
  • depolarise
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24
Q

Ca moving in would do what to the membrane?

A
  • depolarise
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25
Potassium moving out would do what to the membrane?
- repolarise
26
1. What do leaky f channels allow sodium to do?
- allow sodium to diffuse down its concentration gradient = slow depolarisation = if or funny current
27
Are cells in the pacemaker impermeable?
- not impermeable
28
2. As the cell depolarises, f channels close but what happens to continue the depolarisation?
- ca channels open continuing depolarisation
29
3. When the membrane reaches threshold, another type of ca channel opens allowing for what?
- rapid influx - steep depolarisation (the AP)
30
4. At the peak of the depolarisation, ca channels close and what happens next?
- slow potassium channels open = slow repolarisation
31
5. When repolarized, the potassium channels shut and what happens next?
- f channels re-open, starting the next pacemaker potential
32
Spontaneous depolarisation isn't unique to SA node - what has the second highest rate of depolarisation?
- The AV node
33
These are other autonomic foci with their own intrinsic rate - what are these?
- atrial foci (60-80 bpm) - junctional foci ( 40-60 bpm) - ventricular foci (20-40 bpm)
34
The SA node has the fastest intrinsic rate - so what does it do to others and what are the other important in?
- over rides others to set pace - important in cases of arrhythmia
35
What does cardiac muscle look like?
- straited muscle that is involuntary - sarcomeres with actin and myosin - one central nucleus - many mitochondria - good blood supply
36
Cardiac muscle is a functional syncytium - how does its structure aid this function?
- branching cells connected by intercalated discs - cells (myocytes) are coupled via intercalated discs = electrically by gap junctions = mechanically by desmosomes
37
Why does the myocardium need a continuous supply of ATP?
- to support contraction
38
What does branching of fibres in the heart help with?
- helps AP spread
39
Cardiac myocytes are driven - what does this mean?
- no slow depolarisation - they wait for an action potential to reach them via gap junction - the endpoint is contraction
40
What are the characteristics or stages of a membrane potential curve?
1. stable resting potential (more -ve) 2. rapid depolarisation - fast Na channels open 3. notch - fast Na channels close 4. plateau phase - ca2 enters (voltage- sensitive calcium channels) potassium permeability is low 5. repolarisation - potassium leaves (K channels opens calcium channels close)
41
What is the process required for systole?
1. action potential arrives 2. plateau phase and ca2 entry = directly raises cytosol ca2 = also mediates ca2 release from SR 3. binding to troponin, change tropomyosin and reveal myosin binging sites on actin 4. contraction
42
What is the process required for diastole?
-Ca2 - ATPase (enzyme that breaks down ATP) pumps ca2 outside of cell and recycles to SR - facilitated transport ca2/Na antiporter (exchanger) 3:1
43
Excitable cells have a refractory period - what happens here?
- they are unable to respond to new stimulus
44
In skeletal muscles what is the refractory period like?
- quite short
45
Why is it useful to have short refractory periods in skeletal muscle?
- enables new contraction to be initiated before the force of the old one has subsided = tetnay - useful for posture, locomotion
46
In cardiac muscle the long plateau phase and timing of tension development is important. Why do we need a relatively long refractory period in cardiac muscle
- cannot respond to further stimulation - allows atria/ventricles sufficient time to empty and refill before next contraction
47
When the heart in systolic what happens within the chambers?
- they are emptying
48
When the heart is diastolic what is happening in the chambers?
- they are filling
49
What is an electrocardiogram (ECG)?
- measurement of electrical activity of the heart (difference of electricity)
50
Describe the contraction and filling of the heart:
1. atrial contraction 2. isovolumetric contraction 3. rapid ejection 4. reduced ejection 5. isovolumetric relaxation 6. rapid filling 7. reduced filling
51
What are heart sounds associated with?
- associated with valves closing
52
What are S1 and S2 sounds?
* S1 - (lub) = closure of AV valves at (ventricular) systole * S2 - (dub) = closure of semilunar valves at (ventricular) diastole
53
What are the other sounds of the heart that can also be heard?
- S3 - S4
54
Heart sounds depend on what?
- species - age
55
What heart sounds do horses have and dogs and cats?
- horses have all 4 sounds - cats and dogs usually just S1 and S2
56
Abnormal sounds (murmurs) can be due to what?
- leaky valves
57
What are the main features of an ECG?
- p-wave = atrial depolarisation - QRS complex = ventricular depolarisation - T-wave - ventricular repolarisation
58
On an ECG what does a PQ interval equal?
- AV conduction time
59
What cells are not reflected on an ECG?
- pacemaker cells
60
What can an ECG give info on?
- heart rate, rhythm, origin of excitation - spread and decay of excitation - anatomical orientation of heart - relative chamber sizes
61
What can an ECG not give you info on?
- cannot give you info on contractile properties or pumping activity of the heart