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The Heart > Conduction System of the Heart > Flashcards

Conduction System of the Heart Flashcards

1
Q

What does the sinoatrial (SA) node do

A

Spontaneously generate electrical impulses

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2
Q

What is the pacemaker of the cell

A

Sinoatrial (SA) node

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3
Q

Where is the sinoatrial (SA) node located

A

Superior end of the crista terminalis

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4
Q

At what rate does the SA node stimulate contractions

A

70 per minute

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5
Q

What do impulses of the SA node stimulate

A

Contraction of the atria

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6
Q

Where are impulses of the SA conducted to

A

Atrioventricular (AV) node

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7
Q

Where are the AV node located

A

Located at the inferior end of the interatrial septum

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8
Q

Where do the impulses travel after the AV node

A

Conducting fibres from the atrioventricular bundle

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9
Q

What is the other name for the atrioventricular bundle

A

Bundle of His

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10
Q

What does the atrioventricular bundle divide into

A

Two groups of fibres

Right and left bundle branches

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11
Q

What do the left and right bundle branches give rise to

A

Purkinje fibres

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12
Q

Where do the Purkinje fibres enter

A

Myocardium of the left and right ventricles

Stimulate contractions

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13
Q

What is the order of conduction

A

SA node generates electrical impulses

Impulses from SA stimulate contraction of atria

Impulses are conducted to AV node

AV node to atrioventricular bundle to right and left bundle branches to Purkinje fibres

Purkinje fibres enter myocardium of right and left ventricles and stimulate contractions

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14
Q

What is the SA node supplied by

A

Right coronary artery in 60% of people

Left coronary artery in 40% of people

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15
Q

What is the AV node supplied by

A

Posterior interventricular artery

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16
Q

What supplied the bundle of his in most people

A

Left coronary artery

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17
Q

What does sympathetic fibres stimulation cause

A

Increase the heart rate and force of contraction

18
Q

What does parasympathetic fibres stimulation cause

A

Slows the heart rate and force of contraction

19
Q

What is the heart also innervated by

A

Visceral afferent

20
Q

What do visceral afferent fibres convey

A

Sensory information from the heart back to the CNS

21
Q

What is referred pain

A

Pain cannot be pinpointed

Generally felt in left side of neck and or left arm

22
Q

What does a myocyte membrane pump

A

K+ pumped in to the cell

Na+ and Ca2+ pumped OUT the cell

Against conc. gradient (ATP)

23
Q

What causes repolarisation back to the resting potential

A

Outward K+ current

24
Q

Describe a cardiac action potential

A
  1. Resting Potential
    - Na/K ATPase - 2K+ in 3Na+ out
    - Na/K leak channels
  2. Depolarisation
    - large number of Na+ enter the cell (voltage gated Na channel) causing the charge to increase from -90mv to +20mv
  3. Initial repolarisation
    - transient outward current of K+ ions leaving the cell causing a small repolarisation
  4. Plateau
    - Calcium channels open, causing calcium to enter the cell and maintain depolarised state
  5. Repolarisation
    - Outward K+ current causes repolarisation back to resting potential
25
Q

What number stage is resting potential and what happens

A

4

  • Na/K ATPase - 2K+ in 3Na+ out
  • Na/K leak channels
26
Q

What number stage is depolarisation and what happens

A

0

  • large number of Na+ enter the cell (voltage gated Na channel) causing the charge to increase from -90mv to +20mv
27
Q

What stage is initial repolarisation and what happens

A

1

  • transient outward current of K+ ions leaving the cell causing a small repolarisation
28
Q

What stage is plateau and what happens

A

2

  • Calcium channels open, causing calcium to enter the cell and maintain depolarised state
29
Q

What stage is repolarisation and what happens

A

3

  • Outward K+ current causes repolarisation back to resting potential
30
Q

Describe action potential propagation

A
  1. Local depolarisation activates nearby Na+ channels
  2. Influx of sodium ions
  3. Further influx of sodium ions causes a wave of depolarisation

Action potential spreads across membrane

Gap junctions allow cell to cell conduction and propagation of action potential throughout the whole myocardium

31
Q

Describe excitation-contraction coupling

A
  1. influx of calcium through surface ion channels
  2. Amplification of Ca2+ with NaCa
  3. Calcium induced calcium release
32
Q

Describe the troponin-tropomyosin-actin complex

A

Calcium binds to troponin

Conformational change in tropomyosin reveals myosin binding sites

Myosin heads cross-links with actin

Myosin head pivots causing muscle contraction

33
Q

How much longer does cardiac contraction last compared to skeletal muscle

A

15x longer duration

Due to slow calcium channels

Decreased permeability of membrane to potassium after action potential

34
Q

What is the threshold for the SAN

A

35mV

35
Q

What is the phase slop of the SAN affected by

A

Autonomic tone

Drugs

Hypoxia

Electrolytes

Age

36
Q

Delaying of the impulse by the AV node allows for what

A

Atria to empty with blood into the ventricles

Fewer gap junctions

AV fibres are smaller than atrial fibres

  • Limits dangerous tachycardias
37
Q

What is the velocity of conduction by the atrial and ventricular muscle fibres

A

0.3-0.5 m/s

38
Q

What is the velocity of conduction by the purkinje fibres

A

4 m/s

39
Q

How long is the normal refractory period

A

0.25s

40
Q

Why is there a refractory period

A

Allow adequate time for the heart to fill

Prevents excessively frequent contraction

The Heart (12 decks)

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