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Cardiovascular: physiology > Origin and Conduction of Cardiac Impulse > Flashcards

Origin and Conduction of Cardiac Impulse Flashcards

1
Q

what is autorhythmicity?

A

Heart is capable of beating rhythmically in the ABSENCE of external stimuli e.g. nervous stimulation

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2
Q

where does the excitation normally originate?

A

in the specialised pacemaker cells of the sino-atrial node

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3
Q

where is the SA node located?

A

in the upper RIGHT ATRIUM close to where the Superior Vena Cava enters the right atrium

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4
Q

what is a heart controlled by sino atrial node called?

A

said to be in sins rhythm

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5
Q

how does the excitation arise?

A

the cells in the SA node do not have a stable resting membrane potential and therefore exhibit spontaneous pacemaker potential

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6
Q

what must happen for an action potential be generated in the SA nodal cells ?

A

the threshold

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7
Q

what generates the pacemaker potential?

A

decrease in K efflux superimposed on a slow Na influx

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8
Q

what is the rising phase of the AP (i.e. depolarisation) caused by?

A

activation of voltage gates Ca channels which results in Ca influx

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9
Q

what is the falling phase of AP (i.e. repolarisation) caused by?

A

activation o K channels resulting in K efflux

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10
Q

what is the chain of electricity in the heart?

A

SA node - AV node - Bundle of His - left and right branches - purkinje fibres

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11
Q

what is the pacemaker potential?

A

gradual drift of the membrane towards depolarisation

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12
Q

why is there such good cell to cell flow of excitation?

A

because the signals are passed through gap junctions

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13
Q

what anatomical feature is the only point of electrical contact between the atrium and the ventricle?

A

the AV node

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14
Q

what are gap junctions composed of?

A

low resistance protein channels

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15
Q

what is the AV node?

A

a small bundle of specialised cardiac cells

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16
Q

where is the AV node located?

A

at the base of the right atrium; just above the junction of atria and ventricles

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17
Q

how are the AV node cells different from other node cells?

A

they are smaller in diameter and have slow conduction velocity

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18
Q

how are electrical signals passed from SA node to AV node?

A

via gap junctions but there is also some internodal pathways

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19
Q

what does the delay between conduction from the SA to AV allow for?

A

atrial systole to precede ventricular systole

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20
Q

what allows for the rapid spread of action potential to the ventricles?

A

the bundle of His and its branches and the network of purkinje fibres

21
Q

are the APs different in ventricular muscle than nodal cells?

A

YES

22
Q

what is the resting membrane potential for myocytes?

A

-90

23
Q

what results in the extremely rapid depolarisation of the membrane potential of myocytes?

A

fast Na influx

24
Q

what does the myocyte membrane potential then reach?

A

30 mV

25
Q

what is this phase of rapid increase in MP known as?

A

phase 0

26
Q

what is phase 0 of ventricular muscle action potential?

A

fast Na influx

27
Q

what is phase 1 of ventricular muscle action potential?

A

closure of Na channels and transient K efflux

28
Q

what is phase 2 of ventricular muscle action potential?

A

mainly Ca influx

29
Q

what is phase 3 of ventricular muscle action potential?

A

closure of Ca channels and K efflux

30
Q

what is phase 4 of ventricular muscle action potential?

A

resting membrane potential

31
Q

what is the plateau phase ?

A

the MP of ventricular muscle cells is maintained near the peak of action potential for a few hundred milliseconds

32
Q

what is the plateau phase mainly due to?

A

an influx of Ca through voltage gated Ca+ channels

33
Q

what is the falling phase of the AP (repolarisation) caused by?

A

inactivation of Ca channels and activation of K channels

34
Q

which nerve and nervous system exerts a continuous influence on the SA node under resting conditions

A

the vagus nerve - parasympathetic

35
Q

what done the vagal tone do?

A

slows the intrinsic HR from 100bpm to produce a normal resting HR of of 70 bpm

36
Q

what is a resting heart rate of less that 60 called?

A

bradycardia

37
Q

what is a resting heart rate of more than 100 called??

A

tachycardia

38
Q

which cells does the vagus nerve supply in the heatr?

A

SA node and AV node

39
Q

what two things does vagal stimulation do?

A

slows the HR down and increases AV nodal delay

40
Q

what is the neurotransmitter and its receptor for the parasympathetic innervation?

A

acetyl choline acting through M2 receptors

41
Q

what does atropine do?

A

acts as a competitive inhibitor of acetylcholine - used in extreme bradycardia to speed-up the heart

42
Q

how does vagal stimulation slow down the HR?

A

cell hyperpolarises for longer to reach threshold

the slope of pacemaker potential decreases
so the frequency of AP decreases

43
Q

what is this vagal stimulatory effect called?

A

negative chronotrophic effect

44
Q

which cells do the sympathetic nerves supply?

A

the SA node and the AV node and the myocardium

45
Q

what 3 things does the sympathetic stimulation do?

A

increases heart rate and decreases AV nodal delay and increases the force of contraction

46
Q

what is the neurotransmitter and its receptor for the sympathetic innervation?

A

noradrenaline acting on B1 adrenoceptors

47
Q

why does the slope of the pacemaker potential in sympathetic innervation increase?

A

reaches threshold quicker

48
Q

what is an ECG?

A

The ECG is a record of depolarisation and repolarisation cycle of cardiac muscle obtained from skin surface

Cardiovascular: physiology (11 decks)

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