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BMS242 CVS Phys > L9 - Electrical Activity of the Heart > Flashcards

L9 - Electrical Activity of the Heart Flashcards

1
Q

What three type of cells is the electrical activity spread by

A

Nodal cells
Conducting cells
Muscle cells

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2
Q

What type of structures conduct the electrical activity

A

Electrical synapses

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3
Q

Describe the overview of the process of excitation in the heart

A

Initiation at the SA node
Conduction to the atrioventricular node and then to the AV ring
Conduction to the left atria via brachmans bundle (interatrial tract)
Passage through thebundle of His
Purkinje system distributes to the ventricular muscle cells

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4
Q

The SA node acts as a

A

Pacemaker

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5
Q

What is another word for the interatrial tract

A

Brachmans bundle

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6
Q

Describe the location of the SA node

A

Posterior aspect

Junction superior vena cava and right atrium

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7
Q

What is the function of the interatrial tract

A

Spreads the depolarisation from the right atrium to the left atrium

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8
Q

Describe the location of the AV node

A

Posterior aspect - right side inter atrial septum

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9
Q

What are the three subzones of the AV node

A

AV N NV

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10
Q

What is the function of the AV node delay

A

To allow the atrial contraction to finish

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11
Q

What is the function of the AV node refractory period

A

Prevent excess ventricular contraction

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12
Q

What happens to the AV refractoriness as heart rate increases

A

It increase

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13
Q

Subnodal conduction leads to

A

Spetal activation - depolarisation of the septa

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14
Q

What can be said about the contraction of the heart

A

Spiral muscle contraction evoking a torsion

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15
Q

Process of depolarisation in the heart

A

Depolarise the atria
Depolarise in interventricular septum
Depolarisation of the anteroseptal region of the myocardium toward the apex
Ventricles now depolarised
Posterior portion of the base of the left ventricle now depolarised
Depolarisation of the bulk of the ventricular myocardium from the endocardium to the myocardium

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16
Q

Which three types of cells fire action potentials with plateau phases

A

Purkinje fibres

Atrial and ventricular muscle cells

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17
Q

Two properties of pacemaker cells

A

Automaticity

Rhythmicity

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18
Q

What is the primary pacemaker cells of the heart

A

SA node

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19
Q

What other cells are able to act as pacemakers

A

AV node

Purkinje cells

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20
Q

What is the rising phase of a pacemaker cells Vm leading to action potential firing

A

Prepotential

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21
Q

What is responsible for the prepotential

A

Decreased K efflux and increased cation influx

22
Q

What current produces the prepotential

A

If

23
Q

Describe the If current

A

Hypepolarisation induced, inactive when +ve

24
Q

When is the If inactive

A

When +ve

25
Q

What induces IF

A

Hyperpolarisation

26
Q

What is the action potential of a pacemaker cell generated by

A

Fast Ca influx

27
Q

What is repolarisation of the pacemaker cell caused by

A

Increased K efflux

28
Q

What three regualtory mechanisms affect the pacemaker cell action potential

A

Innervation
Temperature
Other pacemaker cells

29
Q

How do vagal fibres affect the pacemaker cells

A

Parasympathetic

Hyperpolarisation of the pacemaker cells and decrease slope of the pre potential

30
Q

How does sympathetic stimulation affect the pacemaker cells

A

Increased prepotential slope and increased firing rate (threshold is reached much faster)

31
Q

What chemical do pacemaker cells rely on

A

cAMP

32
Q

What is the affect of Ach on the pacemaker cells

A

Acts on M2 receptors –> decreased cAMP production

Decreased prepotential slope - longer for threshold to be reached

33
Q

What is the effect of NAdr on the pacemaker cells

A

Acts on beta adrenergic receptors –> increases the cAMP production
Increased prepotential slope - threhsold reached much quicker

34
Q

Describe the action potential of the cardiac muscle

A

No automaticity
Long plateau
Propagated and prolonged action potential
Fast depolarisation and then overshoot

35
Q

What causes the initial depolarisation of the cardiac muscle

A

Opening of the VGNC

36
Q

what leads to a massive depolarisation of the cardiac muscle

A

Opening of many more VGNC

37
Q

When do VGNC close (cardiac muscle

A

When depolarisation peaks

38
Q

What is the peak Vm of the cardiac muscle

A

+30 mV

39
Q

What causes the plateau phase of the cardiac muscle action potential

A

Ca slow channels open and Ca moves into the cell - maintaining the depolarisation

40
Q

Why does the plateau phase of the cardiac muscle AP fall

A

K+ leak

41
Q

What happens when the Ca channels close

cardiac muscle

A

K channels open, K moves out and the cell repolarises

42
Q

What channel is involved with Ina

A

Nav1.5

43
Q

What inhibits Nav1.5

A

TTX and Local anesthetics

44
Q

What channel is involved in Ica

A

Cav1.2

45
Q

What type of channel is Cav1.2

A

L type Ca channel

46
Q

What can said about the number of K channels involved in Ik (repolarising current)

A

Many channels

47
Q

What K channels are the main drivers for membrane repolarisation

A

Iks and Ikr

48
Q

What channel is involved in the funny current

A

HCN4

49
Q

What is HCN4 permeable to

A

Mostly Na some K

50
Q

What is If inhibited by

A

Cs+

BMS242 CVS Phys (12 decks)

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