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Semester 2 > Electrical Properties of The Heart > Flashcards

Electrical Properties of The Heart Flashcards

1
Q

What is the calcium store in muscle?

A

Sarcoplasmic reticulum

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2
Q

What forms the electrical connection in the heart?

A

Gap junctions

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3
Q

What are the intercalating disks formed by?

A

Desmosome followed by gap junction. Desmosome ensures that cells contract at the same time.

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4
Q

Why does cardia muscle have a long action potential?

A

Long refractory period ensures there is no tetanic contraction. Means Ca2+ entry from outside the cell can regulate contraction.

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5
Q

How does Ca2+ entry from outside the cell regulate contraction?

A

impaired thermogenesis and energy expenditure.

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6
Q

What are the cells called with an unstable resting membrane potential?

A

Pacemakers

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7
Q

What causes the wave of electrical activity in the non-pacemaker action potential?

Resting membrane potential?

Initial depolarisation?

Plateau?

Repolarisation?

A

Resting membrane potential - High resting permeability for potassium

Initial depolarisation - Increase in permeability for sodium

Plateau - Increase in permeability for calcium (L - type channels) and decrease in permeability for potassium.

Repolarisation - Decrease in permeability for calcium and increase in permeability for potassium

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8
Q

What causes the wave of electrical activity in the pacemaker action potential?

Action potential?

Pacemaker potential (or pre-potential)?

A

Action potential - increase in permeability for calcium (L-type receptors)

Pacemaker potential (pacemaker potential):

  • Gradual decrease in permeability for potassium
  • Early increase for permeability for sodium (Pf channels)
  • Late increase in calcium in (T-type channels)
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9
Q

When do sodium pF channels open?

A

During repolarisation of the previous action potential

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10
Q

How can drugs affect electrical activity of the heart?

A

–Ca2+-channel blockers – decrease force of contraction – target L type calcium channels – fewer cross bridges formed – smaller strength of contraction

–Cardiac glycocides – increase force of contraction – More calcium comes in - More cross bridges formed– stronger strength of contraction

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11
Q

How does temperature affect the electrical activity of the heart?

A

–increases ~10 beats/min/ºC

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12
Q

How does hyperkalemia affect the electrical activity of the heart?

A

Fibrillation and heart block - reduces concentration gradient for potassium – cell starts to depolarise, spontaneous firing of action potentials

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13
Q

What is the affect of hypokalaemia on electrical activity of the heart?

A

fibrillation & heart block (anomalous) – cells start to hyperpolarise – loads of channels open and the cell depolarises.

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14
Q

What is the affect of hypercalcemia on electrical activity of the heart?

A

–Increased HR & force of contraction – more calcium comes in when the channels open – increase force of contraction.

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15
Q

What is the effect of hypocalcaemia on electrical activity of the heart?

A

–Decreased HR & force of contraction

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16
Q

What is the function of the sinoatrial node?

A

Pacemaker - 0.5 metres per second

17
Q

Describe the annulus fibrosis

A

Non- conduciting insulator between the atria and the ventricles. Action potential can only pass through the atroventricular node.

18
Q

Describe the stages shown

A
19
Q

What is the arterioventricular node?

A

A delay box - 0.05 m/s

20
Q

What is the function of the bundle of his?

A

Bundle of his ensures all the ventricle contracts at the same time

21
Q

What is the name given to the fibres responsible for innervating the ventricular cardiac muscle?

A

•Purkinje fibres

–rapid conduction system

–~ 5 m/sec

22
Q

What is the extracellular effect of an action potential in a single myocyte?

A

eEokes a very small extracellular electrical potential

23
Q

How are large extra-cellular electrical waves created?

A

•Lots of small extracellular electrical potentials evoked by many cells depolarising and repolarising at the same time can summate to create large extracellular electrical waves

24
Q

What does each wave correspond to?

A

P wave corresponds to atrial depolarisation

QRS complex corresponds to ventricular depolarisation

T wave corresponds to ventricular repolarisation

25
Q

What are blocks the result of?

A

Issues in conduction

26
Q

What are flutters and fibrilations due to?

A

Errors in rhythm

27
Q

What is characteristic of atrial fibrillation on an ECG?

A

No distinguishable P wave

28
Q

How does a defibrillator work?

A

Defibrillator puts all the cells into their refractory state – they are now ready to receive the next action potential

29
Q
A

Semester 2 (150 decks)

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