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CVS > L02: Electrical Activity Of The Heart > Flashcards

L02: Electrical Activity Of The Heart Flashcards

1
Q

Describe the pathway of the electrical activity of the heart to create mechanical activity (muscle contraction)

A

1) SAN fires AP whihc propogates to the left and right atrium
2) then to AVN
3) then to bundle of his and purkinje fibres
4) electrical conduction from ventricular endocardium, myocardium and then to epicardium which is the other layer muscle of the heart

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2
Q

What are the 3 main cell types in the heart

A

SAN and AVN cells
Cardiac myocytes
Purkinje fibres

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3
Q

Why is the SAN referred to as a cardiac pacemaker

A

It has no resting membrane potential which allows them to spontaneously generate AP.

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4
Q

If an SAN does not have a resting membrane potential what does it have instead

A

Pacemaker potential

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5
Q

How does the pacemaker potential allow depolarisation

A

It reaches the threshold value quicker

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6
Q

Describe the movement of ions that give the pacemaker potential

A

Inward movement of sodium
Inward movement of calcium
Outward movement of potassium

Overall the inward movement of sodium and calcium exceed potassium excretion

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7
Q

Describe the movement of ions in the SAN at a depolarisation phase

A

Calcium influx via voltage gated calcium channels

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8
Q

Describe the movement of ions at the repolarisation phase

A

Voltage gated calcium channels close

Voltage gated potassium channels open for potassium efflux

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9
Q

Which nervous system innervates the SAN

A

Autonomic nervous system

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10
Q

What are the 2 branches of the autonomic nervous system

A

Sympathetic

Parasympathetic

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11
Q

Which nerve carries the parasympathetic neurones to the SAN

A

Vagus nerve

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12
Q

Which nerve carries the sympathetic neurones to the SAN

A

Cardiac sympathetic nerve

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13
Q

How do we alter the heart rate of the heart

A

By altering the slope of the pacemaker potential

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14
Q

What is the overall effect of the parasympathetic NS to the heart rate

A

Decrease heart rate

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15
Q

What is the overall effect of the sympathetic NS on heart rate

A

Increase heart rate

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16
Q

What neurotransmitter does the parasympathetic nervous system release on post ganglionic neurones

A

Ach

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17
Q

What receptor does ach act on in the heart

A

M2 receptors

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18
Q

What type of neurotransmitter does the post ganglionic sympathetic neurones release

A

NA/ adrenaline

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19
Q

Which receptors does noradrenaline or adrenaline act on in the heart

A

Beta 1 receptors (we have 1 heart)

20
Q

How does the parasympathetic NS decrease the heart rate

A

1) ach released from the vagus nerve acts on M2 receptors on the SAN cells.
2) potassium influx in the ‘pacemaker potential’ increase
3) this reduces the slope of the pacemaker potential so it takes longer to reach threshold and initiate a depolarisation

21
Q

What is the effect of the parasympathetic ns on the pacemaker potential called

A

Negative chronotropic effect

22
Q

How does the sympathetic NS cause an increased heart rate

A

1) NA/A is released from the cardiac sympathetic nerve to the beta-1 receptors on the SAN cells
2) this increases the sodium and calcium influx by opening the channels more (increased conductance)
3) this increases the slope of the pacemaker potential so the threshold value is met quicker for depolarisation to occur

23
Q

What is the effect of the sympathetic nervous system on the pacemaker potential called

A

Positive chronotropic effect

24
Q

List the pacemaker cells in order of the fastest to slowest

A

SAN
AVN
Purkinje fibres

25
Q

Which pacemaker cells drives the heart rate

A

SAN

26
Q

Why do we have a AVN delay

A

To allow the blood in the atrium to fill the ventricles before depolarisation occurs

27
Q

What type of a resting potential does cardiac myocytes have

A

Stable resting potential

28
Q

What initiates cardiac myocytes (in the walls of the heart) to fire action potential

A

Cardiac myocytes receive the voltage of depolarisation from the SAN,AVN and purkinje fibres. This causes VOLTAGE gated sodium channels to open and cause depolarisation

29
Q

What are the phases of ventricular myocyte AP called

A 
Phase 0: rapid depolarisation 
Phase 1: partial rapid repolarisation 
Phase 2: plateau 
Phase 3 : terminal repolarisation 
Phase 4: stable resting potential
30
Q

What causes the rapid depolarisation (phase 0) to occur

A

Fast Voltage gated sodium channels open for sodium influx

31
Q

What causes the partial rapid repolarisation (phase 1)

A

Sodium channels are inactivated

Fast voltage gated potassium channels open for potassium influx

32
Q

What causes the plateau (phase 3)

A

Calcium influx and potassium efflux is balanced

There is no/little change in AP

33
Q

What causes the terminal repolarisation (phase 3) to occur

A

Opening of delayed rectifier potassium channel so potassium efflux occurs more

34
Q

What is the refractory period

A

The period of time from the initial depolarisation to the point of a second depolarisation(AP) to be stimulated

35
Q

What are the 2 types of refractory period

A

Absolute

Relative

36
Q

What is the absolute refractory period

A

No second AP can occur because all the voltage gated sodium channels are closed

37
Q

What is the relative refractory period

A

Second AP can occur as voltage gated sodium channels begin to open/recover

38
Q

What does voltage gated sodium channels need to recover

A

Time

More negative potential (to get to resting membrane potential quicker)

39
Q

If there is a shorter duration so action potential will there be a slower or faster recovery of sodium channels

A

Faster

40
Q

What is a conduction velocity

A

The speed at which an impulse propagates down

41
Q

How are many cardiac myocytes coupled

A

Electrically coupled by GAP junctions

42
Q

What causes the movement of ions between GAP junctions

A

A large voltage gradient

43
Q

What is conduction velocity determined by

A

Charge gradient between cells

Action potential amplitude

44
Q

What is the difference between SAN and cardiac myocytes action potential

A

SAN:

1) pacemaker potential: sodium influx by HCN channels, calcium influx and potassium efflux
2) depolarisation: calcium influx by voltage gated calcium channels
3) repolarisation: potassium efflux by voltage gated potassium channels

Cardiac myocytes:
Has 4 phases:
Phase 0 (depolarisation): sodium influx by voltage gated sodium channel
Phase 1 (rapid partial repolarisation): potassium efflux by voltage gated potassium channel
Phase 2 (plateau): calcium influx= potassium efflux
Phase 3 (terminal repolarisation): potassium efflux by delayed rectifier potassium channels
Phase 4 (resting potential).

45
Q

What is the difference between a positive and negative chronotropic effect

A

Postive chronotropic effect: via the SNS which increases the sodium and calcium influx to give a steep gradient of the pacemaker potential
Negative chronotropic effect: via the PNS which increases potassium efflux to give a less steep pacemaker potential gradient

CVS (19 decks)

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