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Medicine MD3001 cardiovascular system > Physiological Properties of the Heart > Flashcards

Physiological Properties of the Heart Flashcards

1
Q

Describe why the heart is a functional syncytium. What happens if one cell in the syncytium depolarises?

A
  • electrical coupling of the muscle cells in the atria and separately in the ventricles
  • stimulate one region of that muscle to depolarise, because electrically linked,= entire functional unit contracts in synchrony
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2
Q

What is the principle pacemaker of the heart?

A

the Sino atrial node

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3
Q

What does the SA node control? What innervates the SA node?

A
  • spontaneous activity that dictates our heart rate comes from
  • controlled by autonomic innervation
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4
Q

What is the ionic basis for the membrane potential changes in atrial/ventricular muscle?

A
  • rapid upshot from sodium
  • rapid depolarisation by potassium
  • plateau, held at positive potential, maintained by calcium
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5
Q

What is key feature of the action potential in nodal tissue?

A
  • never reaches a stable resting membrane potential

- as membrane potential gets negative it drifts up again to the positive

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6
Q

describe the stages 0-4 of the atrial/ventricular action potential. Mention the ions involved and the channels.

A

0-rapid depolarisation due increased Na permeability, fast Na channels open
1- +20mv=closure of fast Na channels and start of repolarisation, opening of Ca L-type DHP channels
2-influx of Ca, cell can’t repolarise again
3-influx of Ca opens K channels, K floods in to repolarise membrane to resting potential, L-type Ca channels close
4-resting potential, K>Na 50:1

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7
Q

what causes repolarisation in the SA node?

A

due to potassium influx

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8
Q

How does depolarisation occur in the SA node?

A
  • potassium enters cell repolarising membrane potential to negative
  • F-type Na channels open allowing Na influx causing depolarisation to a threshold voltage
  • transient Ca channels open and push the action potential a little higher
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9
Q

What 2 components acting together establish a membrane potential?

A

-F-type channels
-Transient calcium channels
recruit and activate L-type Ca channels, slow, which gradually establish a membrane potential

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10
Q

How do F-type channels operate?

A
  • -sodium channels
  • open as membrane potential decreases towards negative as a result of potassium influx
  • sodium enters causing depolarisation hence preventing membrane potential reaching a resting voltage
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11
Q

How do the SA node and atrial/ventricular action potentials relate?

A

depolarisation in nodal tissue, stimulates through electrical connections the cardiac muscle cells to contract during atrial/ventricular depolarisation

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12
Q

What is the neurotransmitter of the sympathetic nervous system? What receptors does it act on?

A
  • Noradrenaline

- beta 1 receptors

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13
Q

What is substance is produced when noradrenaline acts on B1 receptors?

A

cyclic AMP

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14
Q

what happens as a result of increased cAMP production as a result of sympathetic nervous system?

A
  • recruit protein kinases, phosphorylate certain porteins in the cell
  • proteins which form the channels driving pacemaker potential are phosphorylated
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15
Q

what does increased number of phosphorylated channel proteins result in? Why?

A
  • increased conductance of Ca, Na through F-type, hence increased influx
  • increased effectiveness of channels or increase in channels recruited
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16
Q

How does sympathetic innervation affect the pacemaker action potential?

A

increase rate of discharge and increase speed to get to the threshold potential

17
Q

How does Parasympathetic innervation affect cAMP production? What effect does this have on the ions?

A
  • decrease in production cAMP

- decrease influx of Na and Ca

18
Q

What effect does decreased cAMP production as a result of parasympathetic innervation have on the pacemaker action potential?

A
  • hyper repolarisation
  • decreased protein kinase A due to decreased cAMP decreasing phosphorylation of channel proteins
  • increases extent and duration of K channels opening
19
Q

Where does pacemaker potential spread to? What 2 tracts does it use?

A
  • generated in SA node

- spreads through the atria in interatrial+internodal tracts to AV node

20
Q

What is the AV node? where is it situated?

A
  • only point of electrical connection between atria and ventricles
  • sits at critical point between atria and ventricles in the cardiac skeleton
21
Q

What happens when the electrical signal reaches the AV node? How does it leave?

A
  • signal to be communicated is held in the AV node for a long time
  • rapidly conducted down the R and L bundle of branches of atrioventricular bundle of His
22
Q

What is the anatomical purpose of holding the electrical signal in the AV node for an extended period of time?

A

allows atria to contract in a coordinated fashion followed by ventricular contraction afterwards

23
Q

What is the rate of depolarisation of the SA node?

A

90 beats per min

24
Q

What are the rates of depolarisation of the AV node, His, purnkinjie fibres and the ventricles?

A

AV- 60 beats/min
His- 50 beats/min
purkinjie- 40 beats/min
ventricles- 30 beats/min

25
Q

what is the time for the electrical impulse to get from SA node to Av node?

A

0.03 s

26
Q

what is the impulse delay time in the AV node?

A

0.09s

27
Q

What is the time for impulse t/o penetrate the fibres of the cardiac skeleton?

A

0.04s

28
Q

what is the speed of the penetrating impulse from AV node to reach the bundle of his?

A

0.01m/s

29
Q

what is the speed of conduction down through purkinjie fibres?

A

1.5 - 4m/s

30
Q

how many leads are used in a 12 lead ECG?

A

10

31
Q

How many limb leads are there in a 12 lead ECG? Which lead is the Earth?

A
  • 4

- right leg is Earth lead

32
Q

What is the function of the Earth lead?

A

to eliminate background noise from the ECG trace

33
Q

What happens if there is depolarisation towards the positive end of the lead?

A

will show as an upward trace on the ECG

34
Q

what do the limb leads look at?

A

total sum of the electrical activity in the heart looking at its:

  • size
  • direction of movement
35
Q

How is einhovens triangle formed?

A

lead 1- L to R arm +ve to -ve
Lead 2- L arm to L leg -ve to +ve
lead 3- L leg to R arm +ve to -ve

36
Q

How is electrical activity measured by Einhovens triangle?

A

-measure electrical activity in an area in leads running parallel to that electrical event

Medicine MD3001 cardiovascular system (44 decks)

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