Physiological Properties of the Heart Flashcards

1
Q

Phase 0 of atrioventricular depolarisation

A

rapid depolarisation due to increased sodium ion permeability as fast as the channels open

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2
Q

Phase 1 of atrioventricular depolarisation

A

start of repolarisation as fast as sodium ion channels close

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3
Q

Phase 2 of atrioventricular depolarisation

A

L-type calcium ion channels triggered by change in voltage and calcium enters cell

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4
Q

Phase 3 of atrioventricular depolarisation

A
  • rapid repolarisation as the intracellular calcium ion concentration increases
  • stimulates potassium ion channels to open and the potassium permeability increases
  • calcium ion channels close
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5
Q

Phase 4 of atrioventricular depolarisation

A

stable resting membrane potential where potassium ion permeability exceeds sodium ion permeability

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6
Q

Phase 1 of SA node depolarisation to create the pacemaker potential

A
  • gradual increase in resting membrane as sodium ion permeability increases as f-type sodium ion channels open
  • and decrease in potassium ion permeability as potassium ion channels close
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7
Q

What helps establish the pacemaker potential in phase 1 SA node depolarisation?

A

transient calcium ion channels

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8
Q

Phase 2 of SA node depolarisation

A

moderately rapid depolarisation due to calcium ion entry by slow L channels

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9
Q

Phase 3 of SA node depolarisation

A

rapid repolarisation as increased intracellular calcium ion concentration stimulates opening of potassium ion channels and an increase in potassium ion permeability

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10
Q

What nerve innervates the SA and AV node?

A

Parasympathetic innervation by the vagus nerve

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11
Q

How does sympathetic stimulation affect pacemaker activity?

A
  • increases calcium ion permeability
  • increases sodium ion permeability by f-type channels
  • increases rate of SAN phase 1 depolarisation (positive chronotropic effect)
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12
Q

How does parasympathetic stimulation affect pacemaker activity?

A
  • hyperpolarises membrane potential to lower starting level
  • increases extent and duration of opening of potassium ion channels therefore increasing the permeability of potassium ions
  • decreases rate of SAN phase 1 depolarisation (negative chronotropic effect)
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13
Q

How does the sympathetic NS stimulate pacemaker activity?

A

noradrenaline acts on B1 receptors to increase cAMP production

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14
Q

How does the parasympathetic NS stimulate pacemaker activity?

A

Acetylcholine on M2 receptors which decrease cAMP production

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15
Q

During AV node conduction where is the biggest delay?

A

When passing the AV node

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16
Q

How to measure electrical activity non-invasively

A
  • electrocardiogram (ECG)
  • uses electrodes (4 on the limbs, 6 across the chest)
  • limb leads measure sum of electrical activity of heart and direction the activity is moving in
  • one lead is designated positive
17
Q

How to calculate the strength of the electrical activity

A

observed signal is equal to the electrical event multiplies by the angle between the event and ECG lead

18
Q

What determines the strength of electrical activity?

A
  • current

- direction of signal