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Cardio > Origin and Conduction of Cardiac Impulse > Flashcards

Origin and Conduction of Cardiac Impulse Flashcards

1
Q

What is the heart?

A

Electrically controlled muscular pump which sucks and pumps blood

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2
Q

Where are the electrical signals which control the heart generated?

A

Within the heart

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3
Q

What is autorhythmicity?

A

Heart is capable of beating rhythmically in the absence of external stimuli

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4
Q

Where does excitation of the heart normally begin?

A

Pacemaker cells in the sinoatrial node

Clusters of these cells initiate the heart beat

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5
Q

Where is the SA node situated?

A

Upper right atrium close to where superior vena cava enters the right atrium

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6
Q

What does the SA normally do?

A

Drives the entire heart rate (sets the pace)

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7
Q

What does it mean if a heart is in sinus rhythm?

A

Heart controlled by sino atrial node

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8
Q

Role and characteristics of cells in SA node?

A

No stable resting membrane potential

They generate regular spontaneous pacemaker potentials

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9
Q

What happens when a spontaneous pacemaker potential is generated?

A

It takes the membrane potential to a threshold and every time a threshold is reached an action potential is generated

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10
Q

What does an action potential being produced result in?

A

Generation of regular spontaneous action potentials in the SA nodal cells

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11
Q

Permeability to K+ in pacemaker cells?

A

Does not remain the same between action potentials

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12
Q

Pacemaker potential?

A

Slow depolarization of membrane potential to a threshold

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13
Q

Pacemaker potential?

A

Slow depolarization of membrane potential to a threshold

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14
Q

What does pacemaker potential look like on a diagram?

A

It is the beginning of a slight incline between two rises (-60mV->-40mV)

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15
Q

What does pacemaker potential look like on a diagram?

A

It is the beginning of a slight incline between two rises (-60mV->-40mV)

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16
Q

Ionic basis for a pacemaker action potential?

A

Once the threshold is reached:

  • The rising phase (depolarization) of action potential is caused by activation of long-lasting L type Ca++ channels
  • Resulting in Ca++ influx
  • The falling phase (re-polarization) is caused by inactivation of L-type Ca++ channels and
  • Activation of K+ channels resulting in K+ efflux
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17
Q

What is threshold?

A

-40mV

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18
Q

General description of how cardiac excitation spreads through heart?

A 
starts at SA node 
Passes by cell to cell conduction to get to the AV node
Then travels to the Bundle of His 
then down the left and right branches 
and to the purkinje fibers
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19
Q

Cell to cell excitation via GAP junctions?

A

From SA node through both atria
From SA node to AV node
Within ventricles

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20
Q

What is the AV node?

A

Bundle of specialized cardiac cells located at the base of the right atrium just above junction of atria and ventricles

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21
Q

What is special about AV node?

A

ONLY point of electrical contact between atria and ventricles

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22
Q

Spread of excitation across atria?

A

Mainly cell to cell via gap junctions

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23
Q

Spread of excitation from SA node to AV node?

A

Mainly cell to cell conduction via gap junctions but also some inter-nodal pathways

24
Q

What happens to conduction in AV node?

A

It is delayed - this allows atrial systole (contraction) to precede ventricular systole

25
Q

What do Bundle of His and Purkinje fibres allow?

A

Rapid spread of action potential to the ventricles

26
Q

Spread of excitation across ventricular muscle?

A

Cell to cell conduction

27
Q

Action potential in contractile cardiac cells and pacemaker cells?

A

Differ considerably

28
Q

Resting membrane potential of atrial and ventricular myocytes?

A

-90mV until excitation

29
Q

Depolarization of myocytes? and it’s name

A
  • Caused by fast Na+ influx
  • Rapidly reverses membrane potential to +20mV
  • Phase 0 of AP in contractile cardiac muscle cells
30
Q

Phases of ventricular muscle AP?

A

Phase 0- fast influx of Na+
Phase 1- Closure of Na+ channels and transient K+ efflux
Phase 2- Mainly Ca++ influx
Phase 3- Closure of Ca++ channels and K+ efflux
Phase 4- Resting membrane potential

31
Q

Phase 0=

A

Fast influx of Na+

32
Q

Phase 1=

A

Closure of Na+ channels and transient K+ efflux

33
Q

Phase 2=

A

Mainly Ca++ influx

34
Q

Phase 3=

A

Closure of Ca++ channels and K+ efflux

35
Q

Phase 4=

A

Resting membrane potential

36
Q

Plateau phase of action potential?

A
  • Membrane potential maintained near the peak of AP for a few 100 milliseconds
  • Unique characteristic of contractile cardiac muscle cells
  • Mainly due to influx of Ca++ through L type Ca++ channels
37
Q

Falling phase of ventricular muscle action potential?

A

Repolarization is caused by inactivation of Ca++ channels and activation of K+ channels= K+ efflux

38
Q

What is the heart rate mainly influenced by?

A

Autonomic nervous system

39
Q

What does sympathetic stimulation do to heart rate?

A

Increases HR

40
Q

What does parasympathetic stimulation do to heart rate?

A

Decreases HR

41
Q

What do changes of the heart rate usually involve?

A

Reciprocal action of sympathetics and parasympathetics

42
Q

What does the vagus nerve do?

A

Parasympathetic supply to the heart

Exerts a continuous influence on the SA node under resting conditions

43
Q

Vagal tone under normal resting conditions?

A

Dominates

44
Q

What does vagal stimulation do?

A

Slows the intrinsic heart rate from ~100bpm to produce normal resting HR and increases AV nodal delay

45
Q

Bradycardia

A

Resting heart rate less than 60bpm

46
Q

Tachycardia

A

Resting heart rate over 100bpm

47
Q

What does the vagus nerve supply?

A

AV and SA node

48
Q

Parasympathetic supply of heart

A

Vagus nerve

Neurotransmitter= Acetylcholine acting through muscarinic M2 receptors

49
Q

Atropine?

A

Competitive inhibitor of acetyl choline used in extreme bradycardia to speed up the heart

50
Q

What do negative chronotropes do?

A

Decrease HR

51
Q

What do cardiac sympathetic nerves supply?

A

AV node, SA node and myocardium

52
Q

What does sympathetic stimulation do?

A

Increases HR
Decrease AV nodal delay
Force of contraction

53
Q

Sympathetic Neurotransmitter?

A

Noraderinaline acting through B1 adrenoceptors

54
Q

Effect of sympathetic nervous system on HR in detail?

A

Increases=

  • Slope of pacemaker potential
  • Heart rate
  • Pacemaker cell Na+ & Ca++ influx

Decreases=

  • Pacemaker cell K+ influx
  • AV nodal delay
55
Q

Effect of parasympathetic nervous system on HR in detail?

A

Increases=

  • Pacemaker cell K+ influx
  • AV nodal display

Decreases=

  • Slope of pacemaker potential
  • Heart rate
  • Pacemaker cell Na+ & Ca++ influx
56
Q

What is the ECG?

A

Record of depolarization and repolarisation cycle of cardiac muscle obtained from skin surface

57
Q

How to record ECG?

A

lead 1: RA to LA
Lead 2: RA to LL
Lead 3: LA to RL

Cardio (36 decks)

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