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Cardio - week 1/2 > origin and conduction of cardiac impulse > Flashcards

origin and conduction of cardiac impulse Flashcards

1
Q

What is autorhythmicity?

A

the heart beating rhythmically in the absence of external stimuli

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2
Q

where in the heart does the excitation normally originate?

A

pacemakers cells within the sino-atrial node

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3
Q

what do the specialised pacemaker cells within the SA node do?

A

initiate the heart beat

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4
Q

where can the SA node be found?

A

the right upper atrium close to the entry point of the superior vena cava

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5
Q

how would you describe a heart that is controlled by the sino-atrial node?

A

it is said to be in sinus rhythm

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6
Q

how does cardiac excitation normally originate?

A
  1. cells in the SA node generate regular spontaneous pacemaker potentials
  2. pacemaker potential takes the membrane potential to a threshold
  3. each time the threshold is reached an action potential is generated
  4. = generation of regular spontaneous action potentials in SA nodal cells
  5. once threshold is reached, it causes depolarisation
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7
Q

what is the pacemaker potential?

A

the slow depolarisation of membrane potential to a threshold

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8
Q

what is depolarisation caused by?

A

DECREASE in K+ EFFLUX
Na+ and K+ INFLUX (the funny current)
TRANSIENT Ca++ INFLUX (T-type Ca++ channels)
- fast Na+ influx

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9
Q

what is the falling phase of action potentials?

A

repolarisation

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10
Q

what is repolarisation caused by?

A
  • Inactivation of L-type Ca++ channels and

- Activation of K+ CHANNELS. Resulting in K+ EFFLUX

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11
Q

how does excitation spread from cell to cell?

A
  1. from SA node through both atria
  2. from SA node to AV node within ventricles
    ^^ both via gap junctions
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12
Q

what is the AV node and where is it located?

A
  • a small bundle of specialised cardiac cells -> small in diameter, has slow conduction velocity
  • located at the base of the right atrium, just above the junction of atria and ventricles
  • only point of electrical contact between atria and ventricles
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13
Q

describe the spread of excitation on a whole

A
  1. Across the atria mainly cell-to-cell conduction via gap junctions
  2. From SA node to AV node: mainly cell-to-cell conduction via gap junctions; but there is also some internodal pathways
  3. The conduction is delayed in the AV node. This allows atrial systole (contraction) to precede ventricular systole
  4. The Bundle of His and its branches and the network of Purkinje fibers allow rapid spread of action potential to the ventricles
  5. Ventricular muscle: cell-to-cell conduction
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14
Q

what is the resting membrane potential of the cell (before it is excited)

A

-90mV

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15
Q

what is the membrane potential just after it has been excited

A

+20mV

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16
Q

what is the plateau phase of action potential?

A

when the membrane potential is maintained near the peak of action potential for few hundred milliseconds
-> unique characteristic of contractile cardiac muscle cells

17
Q

what is the plateau phase of action potential due to?

A

influx of Ca++ through L-type Ca++ channels

18
Q

what changes the heart rate?

A
  1. mainly influenced by the autonomic nervous system
  2. sympathetic stimulations increases HR
  3. parasympathetic stimulation decreases HR
  4. vagal tone slows the intrinsic HR from 100bpm to produce a normal resting HR f 70 bpm
19
Q

what is vagal tone?

A

it refers to the activity of the vagus nerve

20
Q

describe the normal, low and high resting heart rates

A
  • normal= 60-100 bpm
  • bradycardia (slow) = <60 bpm
  • tachycardia (fast) = >100 bpm
21
Q

what is atropine and when is it used?

A
  • competitive inhibitor of acetylcholine

- used in extreme bradycardia to speed up the heart

22
Q

what does the cardia sympathetic nerve supply?

A
  • SA node
  • AV node
  • myocardium
23
Q

what does sympatheic stimulation do and what is the neurotransmitter associated with it?

A
  • increase HR
  • decrease AV nodal delay
  • Noradrenaline
24
Q

what does vagal stimulation do? (parasympathetic supply of the heart)

A
  • increase HR

- increase AV nodal delay

25
Q

what is the neurotransmitter asociated with the parasympathetic nervous system

A

acetyl-choline

26
Q

what is the effect of vagal stimulation on pacemaker potentials?

A
  • cell hyperpolarises
  • longer to reach threshold
  • slope of pacemaker potential decreases
  • frequency of AP decreases
  • negative chronotropic effect
27
Q

what is the effect of noradrenaline on pacemaker potentials?

A
  • ** slope of pacemaker potential increases**
  • pacemaker potential reaches threshold quicker
  • frequency of action potentials increases
  • positive chronotropic effect

Cardio - week 1/2 (9 decks)

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