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1st year systems ADAM > 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 same time.

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4
Q

Why does cardia muscle have a long action potential?

A

Long refractory period = no tetanic contraction

Means Ca2+ entry from outside cell can regulate contraction

The reason why cardiac muscle has a longer action potential is to extend the absolute refractory period to prevent another action potential. If too many action potentials stimulate the cardiac muscle it can get into tetanus which keeps the heart continuously contracted without relaxation.

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5
Q

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

A

Ca2+ release does not saturate the troponin in cardiac muscle

Regulation of Ca2+ release used to vary strength of contraction

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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 previous action potential

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10
Q

How can drugs affect electrical activity of the heart?

Ca2+ channel blockers

A

Decrease force of contraction

Target L type calcium channels

Fewer cross bridges formed

Smaller strength of contraction

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11
Q
A

-Cardiac glycocides

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12
Q

How does temperature affect the electrical activity of the heart?

A

–increases ~10 beats/min/ºC

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13
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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14
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

Cell depolarises.

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15
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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16
Q

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

A

Decreased HR

Force of contraction

17
Q

What is the function of the sinoatrial node?

A

Pacemaker - 0.5 metres per second

18
Q

Describe the annulus fibrosis

A

Non- conducting insulator between atria & ventricles

Action potential pass through atrioventricular node

19
Q

Describe the stages shown

A
20
Q

What is the arterioventricular node?

A

A delay box - 0.05 m/s

21
Q

What is the function of the bundle of his?

A

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

22
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

23
Q

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

A

Evokes a very small extracellular electrical potential

24
Q

How are large extra-cellular electrical waves created?

A

Lots of small extracellular electrical potentials evoked by many cells depolarising

Repolarise at same time to summate to create large extracellular electrical waves

25
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

26
Q

What are blocks the result of?

A

Issues in conduction

27
Q

What are flutters and fibrilations due to?

A

Errors in rhythm

Atrial flutter
28
Q

What is characteristic of atrial fibrillation on an ECG?

A

No distinguishable P wave

29
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

30
Q

what does ventricular fibrillation look like

A

1st year systems ADAM (52 decks)

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