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CVS > 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 cells contract at the same time

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4
Q

Why does cardiac muscle have a long action potential?

A

Long refractory period ensures 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:

  1. Resting membrane potential?
  2. Initial depolarisation?
  3. Plateau?
  4. Repolarisation?
A
  1. High resting permeability for potassium
  2. Increase in permeability for sodium
  3. Increase in permeability for calcium (L - type channels), decrease in permeability for potassium
  4. 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?

A

Action potential

  • increase in permeability for calcium (L-type receptors)
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9
Q

What causes the wave of electrical activity in the Pacemaker potential (or pre-potential)?

A

Pacemaker potential (pacemaker potential):

  • Gradual decrease in permeability for potassium
  • Early increase for permeability for sodium (Pf channels)
  • Late increase in permeability for calcium (T-type channels)
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10
Q

When do sodium pF channels open?

A

repolarisation of previous action potential

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11
Q

How can Ca2+ channel blocking 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
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12
Q

How can cardiac glycoside drugs affect electrical activity of the heart?

A

Cardiac glycocides

  • increase force of contraction
  • More calcium comes in - More cross bridges formed
  • stronger strength of contraction
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13
Q

How does temperature affect the electrical activity of the heart?

A

increases ~10 beats/min/ºC

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14
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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15
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 cell depolarises

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16
Q

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

A

Increased HR & force of contraction

more calcium comes in when channels open

17
Q

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

A

Decreased HR & force of contraction

18
Q

What is the function of the sinoatrial node?

A

Pacemaker - 0.5 metres per second

19
Q

Describe the annulus fibrosis

A

Non- conducting insulator between atria and ventricles

Action potential can only pass through atrioventricular node

20
Q

Describe the stages shown

21
Q

What is the arterioventricular node?

A

delay box - 0.05 m/s

22
Q

What is the function of the bundle of his?

A

ensures whole ventricle contracts at the same time

23
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
24
Q

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

A

Evokes very small extracellular electrical potential

25
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

26
Q

What does each wave correspond to?

A

P wave - atrial depolarisation

QRS complex - ventricular depolarisation

T wave - ventricular repolarisation

27
Q

What are blocks the result of?

A

Issues in conduction

28
Q

What are flutters and fibrilations due to?

A

Errors in rhythm

29
Q

What is characteristic of atrial fibrillation on an ECG?

A

No distinguishable P wave

30
Q

How does a defibrillator work?

A

Defibrillator puts all cells into refractory state

Now ready to receive next action potential

CVS (26 decks)

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