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Cardiovascular Physiology > Cardiac impulse > Flashcards

Cardiac impulse Flashcards

1
Q

What is Audtorhythmicity?

A

The heart is capable of beating by itself, it does not need any external stimuli.

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2
Q

Where does the heart beat initiate from?

A

Excitation of the pacemaker cells in the Sino-Atrial node initiates the heart beat.

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3
Q

Where is the SA node located?

A

The upper right atrium, close to where the Superior Vena Cava enters.

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4
Q

What is Sinus Rhythm?

A

It is when the heart is controlled by the SA node.

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5
Q

What is the Pacemaker Potential?

A

It is the slow depolarisation of the membrane potential towards a threshold.

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6
Q

What causes the depolarisation in the pacemaker potential?

A

Decrease in k+ efflux
Na+ and K+ influx (funny current)
Transient Ca++ influx (t type channels)

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7
Q

What occurs once the pacemaker potential has reached the threshold?

A

The rising phase of Action Potential

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8
Q

What causes the rising phase of action potential?

A

Long lasting l type Ca++ channels causing a Ca++ influx.

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9
Q

What is the falling phase of action potential caused by?

A

Inactivation of l type Ca++ channels (efflux)

Activation of K+ channels (efflux)

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10
Q

How does the electrical impulse of the SA node reach the AV node?

A

Cell-to-cell conduction

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11
Q

What is the pathway of the impulse once it reaches the AV node?

A

AV node
Bundle of His
Left and Right Branches
Purkinje Fibres

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12
Q

What is the AV node composed of?

A

Specialised cardiac cells

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13
Q

Where is the AV node located?

A

The base of the right atrium just above the junctions of the atria and ventricles

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14
Q

Why is the AV node the only electrical point of contact between the atria and ventricles?

A

The fibrous links do not allow action potential to pass through.

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15
Q

Where does the spread of excitation arise from?

A

Cell to cell interactions via gap junctions and some internodal pathways.

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16
Q

What does the delayed conduction in the AV node allow for?

A

Allows for the atria to contract (systole)

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17
Q

What do the bundle of His and purkinjie fibres allow for?

A

The rapid spread of action potential to the ventricles.

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18
Q

What is the resting membrane potential in cardiac cells before the are excited?

A

-90mV

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19
Q

What phase is the rising phase of action potential in the cardiac muscle cells and what is it caused by?

A

Phase 0 and it’s due to a fast Na+ influx.

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20
Q

What is Phase 1?

A

The closure of Na+ channels and transient K+ efflux

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21
Q

What is Phase 2?

A

Mainly Ca++ influx (Plateau phase)

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22
Q

What is Phase 3?

A

The closure of Ca++ channels and K+ efflux (falling Phase)

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23
Q

What is Phase 4?

A

Resetting the membrane potential

24
Q

What is the plateau phase of the action potential?

A

Membrane potential maintained near the peak of the action potential for a few 100 milliseconds. It is a unique characteristic of contractile cardiac cells.
It is due to the influx of Ca++ through l type channels.

25
Q

What causes the falling Phase of the action potential?

A

Inactivation of Ca++ channels and activation of K+ channels (efflux)

26
Q

What influences heart rate?

A

The autonomic nervous system

27
Q

What noes the sympathetic nervous system do to heart rate?

A

Speeds it up

28
Q

What does the parasympathetic nervous system do to heart rate?

A

Slows it down

29
Q

What is the parasympathetic supply to the heart?

A

The vagus nerve

30
Q

What does the vagal tone do?

A

Slows the intrinsic heart rate from 100 to resting of 70

31
Q

What is a normal resting heart rate?

A

60-100bpm

32
Q

What is Bradycardia?

A

When the HR is below 60 bpm

33
Q

What is Tachycardia?

A

When the HR is above 100 bpm

34
Q

What does Vagal stimulation do?

A

Slows the heart and increases AV nodal delay

35
Q

How does Acetylcholine act?

A

Through muscarinic M2 receptors

36
Q

What is Atropine?

A

A competitive inhibitor of acetylcholine

37
Q

When would atropine be prescribed?

A

In extreme bradycardia to speed up the heart

38
Q

What does stimulating the vagal nerve do in terms of the rate of firing?

A

The rate of firing slows
The cell
Hyperpolarises and it takes longer to reach the threshold
The slope of the pacemaker potential decreases (flattens)
It has a negative chronotropic effect

39
Q

What is a negative chronotropic effect?

A

Slows the HR

40
Q

What do the cardiac sympathetic cells supply?

A

The SA and AV nodes and the myocardium

41
Q

What do the cardiac sympathetic cells do?

A

Increase the HR and decreases AV nodal delay

Increases force of contraction

42
Q

What does noradrenaline act through?

A

B1 adrenoceptors

43
Q

What impact does the stimulation of the cardiac sympathetic cells have?

A

The slope of the pacemaker potential increases (steep)
Threshold is reached quicker
The frequency of action potentials increases
Positive chronotropic effect

44
Q

What is a positive chronotropic effect?

A

Increase in HR

45
Q

What is an RCG?

A

An electrocardiogram

46
Q

What is an ECG a record of?

A

The depolarisation and repoalrisation of the cycle of cardiac muscle obtained from the skin surface

47
Q

What are the electrodes places on the skin surface (Standard Limb Leads)

A

Lead 1- RA/LA
Lead 2- RA/LA
Lead 3- LA/LL

48
Q

How many standard limb leads are there?

A

3

49
Q

What limb remains earthed in an ECG

A

Right leg

50
Q

In an ECG what does P indicate?

A

Atrial depolarisation

51
Q

In an ECG what does the QRS complex show?

A

Ventricular depolarisation (masks atrial repolarisation

52
Q

In an ECG what does T indicate?

A

Ventricular repolarisation

53
Q

In an ECG what does the PR interval show?

A

The AV nodal delay

54
Q

In an ECG what does the ST segment show

A

Ventricular systole

55
Q

In an ECG what does TP interval show?

A

Diastole

56
Q

Why does the ECG not pick up atrial repolarisation?

A

It is masked by atrial repolarisation and is so small it cannot he detected by the skin

Cardiovascular Physiology (5 decks)

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