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Cardiovascular Week 1 & 2 2016/17 > READ ME / 1: Origin and conduction of cardiac impulses > Flashcards

READ ME / 1: Origin and conduction of cardiac impulses Flashcards

1
Q

Thanks for using my flashcards, hope you find them useful!

If you spot any errors or have suggestions, please let me know by clicking the speech bubble or sending me a message. It’s really helpful.

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2
Q

The questions are written using the official Dundee lectures, so you might find it useful to have them open in the background in case you get stuck.

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3
Q

I write the questions based on what I think the important facts are, but not everything is relevant. Don’t waste your time learning tiny details.

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4
Q

On the other hand, this isn’t everything you need to know - back it up with stuff from tutorials, other people’s questions, Youtube videos, Oxford handbooks etc.

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5
Q

There’s a good chance that older decks will be inaccurate (lectures and guidelines change year to year) so I’ll try to update them in the future.

Break a leg 👍

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6
Q

What is the function of the heart?

A

Muscle pump - contracts to push blood through the circulation

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7
Q

The pumping of the heart is controlled by electrical impulses.

Where in the body are they generated?

A

Within the heart

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8
Q

What is autorhythmicity?

A

The heart generates its own electrical impulses - doesn’t require anything else to beat

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9
Q

The heart can beat without any external stimuli - what is this called?

A

Autorhythmicity

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10
Q

Which chamber of the heart do electrical impulses start in?

What is the specific area called?

Which type of cell is found in this area?

A

Right atrium

Sino-atrial node (SA node)

Pacemaker cells

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11
Q

What do pacemaker cells initiate and where are they found?

A

Heartbeat

Found in SA node of right atrium

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12
Q

Where is the sino-atrial node (SA node) found?

A

Right atrium

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13
Q

Which great vessel of the heart is the SA node closely related to?

A

Superior vena cava (SVC)

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14
Q

The SA node normally determines the heart’s ___.

A

rate

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15
Q

A heart controlled by the SA node is said to be in which type of rhythm?

A

Sinus rhythm

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16
Q

What is the arrow pointing to?

A

Sino-atrial node (SA node)

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17
Q

What is the membrane potential of a cell?

A

Difference in ion concentrations inside and outside the cell, generating an electrical current

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18
Q

Pacemaker cells in the SA node (have / don’t have) a stable membrane potential.

A

don’t have a stable membrane potential

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19
Q

What are the two changes in membrane potential seen in SA node cells?

A
  1. Spontaneous pacemaker potential - slowly increases towards threshold
  2. Action potential - rapid change in potential which occurs when the threshold is reached
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20
Q

What happens after the threshold potential of SA node cells is reached?

A

Action potential - generation of a nerve impulse

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21
Q

Name A and B.

A

A - pacemaker potential

B - action potential

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22
Q

Is the action potential of an SA nodal cell a depolarisation, hyperpolarisation or repolarisation?

A

Depolarisation

(Hyperpolarisation - going from negative to even more negative

Repolarisation - going from positive back to negative

Depolarisation - going from negative to positive)

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23
Q

The pacemaker potential is caused by three changes in ion concentration - what are they?

A

1) Decrease in K+ efflux (less potassium OUT)
2) Na+<strong> </strong>and K+ influx (sodium and potassium IN)
3) Transient Ca2+ influx (calcium IN through T-type channels)

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24
Q

During spontaneous pacemaker potential, sodium and potassium ions enter the cell causing slow depolarisation - what is this called?

A

Funny current

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25
Q

During the spontaneous pacemaker potential, calcium ions enter the cell through which type of channel?

A

T-type Ca2+ channels

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26
Q

During the pacemaker action potential, what causes the rising phase (i.e the depolarisation) and which channel is responsible?

A

Ca2+ influx caused by the activation of L-type calcium channels

(Remember the T-type channels are involved in the spontaneous part only)

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27
Q

Two events cause the falling phase (i.e the repolarisation) of a pacemaker action potential - what are these and which channels are responsible?

A

1) Inactivation of L-type Ca++ channels - no more calcium IN
2) Activation of K+ channels - causes K+ efflux - more potassium OUT

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28
Q

There are two kinds of calcium channel - what are they called and which processes are they responsible for?

A

T-type - involved in spontaneous pacemaker potential

L-type - involved in pacemaker action potential

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29
Q

Where is the atrioventricular node (AV node) found?

A

Base of the right atrium

At the wall between the right and left atrium, also called the inter-atrial septum

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30
Q

How are action potentials carried from the SA node to the AV node?

A

Conduction between cells via Gap junctions

31
Q

What structures allow action potentials to travel between cells?

A

Gap junctions

32
Q

Which node is found at the base of the right atrium?

A

AV node

33
Q

Which node is found in the upper right atrium?

A

SA node

34
Q

The AV node is the only point of electrical contact between which two heart structures?

A

Atria

Ventricles

35
Q

Does the AV node transmit electrical impulses immediately?

A

No - there’s a delay

Vital so that the heart contracts rhythmically

36
Q

___ systole precedes ___ systole due to delayed conduction in the AV node.

(systole = contraction of muscle and ejection of blood)

A

Atrial systole precedes Ventricular systole

37
Q

Through which structure do action potentials travel across the interventricular septum?

A

Bundle of His

38
Q

Name the sequence of structures along which an action potential travels before reaching the terminal nerves of the heart (and include the name of them!)

A

SA node

AV node

Bundle of His

Right and left bundle branches

Terminal nerves = Purkinje fibres

39
Q

The Bundle of His and Purkinje fibres allow ___ spread of action potential to the ventricles.

A

rapid

40
Q

How do action potentials travel through the ventricular muscle of the heart?

A

Cell-to-cell conduction via gap junctions

41
Q

Apart from pacemaker cells, a different type of cardiac cell generate action potentials - what are they called?

A

Cardiac myocytes

i.e the main bulk of cardiac muscle

42
Q

The resting membrane potential of cardiac myocytes remains at __mV until the cell is excited.

A

-90mV

Remember membrane potential of potassium is -90, membrane potential of sodium is +60

Cell is always trying to get rid of sodium via sodium-potassium pump, so resting membrane potential is usually CLOSER to potassium’s (i.e really negative)

43
Q

What causes the rising phase of action potential (i.e depolarisation) in cardiac myocytes?

A

Fast Na+ influx

44
Q

After depolarisation, the membrane potential of cardiac myocytes has changed from -__mV to +__mV.

A
  • 90mV to +20mV
    i. e potassium’s potential to sodium’s potential (because a ton of sodium has just entered the cell)
45
Q

What happens in Phase 0 of the action potential in cardiac myocytes?

A

Fast Na+ influx causing depolarisation

46
Q

This graph shows the membrane potential of ventricular muscle during an action potential - describe what happens to cause the numbered phases shown on the graph.

A

Phase 0: fast influx of Na+

Phase 1: closure of Na+ channels and transient efflux of K+

Phase 2: mainly Ca++ influx through L-type channels

Phase 3: closure of Ca++ channels and K+ efflux

Phase 4: resting membrane potential

47
Q

In cardiac myocytes, the membrane potential is maintained near the peak of action potential for a few hundred milliseconds - what is this phase called?

A

Plateau phase

48
Q

The plateau phase is a unique characteristic of which cell’s action potential?

A

Cardiac myocytes

49
Q

What causes the plateau phase of action potentials in cardiac myocytes?

Which Phase of the action potential does it line up with?

A

Influx of Ca2+ through L-type channels

Phase 2

50
Q

What causes the falling phase of action potential (i.e the repolarisation) in cardiac myocytes?

A

(Closure of L-type Ca2+ channels)

K+ efflux

51
Q

Heart rate is mainly influenced by the _____ nervous system.

A

autonomic

(Autonomic nervous system supplies the MOTOR aspect of the internal organs and is split into the sympathetic and parasympathetic arms, lots more of this throughout the year so dw)

52
Q

Which kind of autonomic nervous stimulation increases heart rate?

A

Sympathetic stimulation

(think “fight or flight”)

53
Q

Sympathetic stimulation (increases / decreases) heart rate.

A

increases

54
Q

Which kind of autonomic nervous stimulation decreases heart rate?

A

Parasympathetic

55
Q

Parasympathetic stimulation (increases / decreases) heart rate.

A

decreases

56
Q

Which cranial nerve gives the parasympathetic supply to the heart?

A

CN X

(Vagus nerve)

57
Q

The vagus nerve (CN X) exerts a continuous influence on which node of the heart?

A

SA node

58
Q

The vagal tone slows the heart rate from around 100bpm to its normal resting heart rate of __bpm.

A

70 bpm

59
Q

What is the normal range for resting heart rate?

A

60 - 100 bpm

60
Q

When a patient’s heart rate is found to be < 60 bpm they are said to be…

A

bradycardic

61
Q

When a patient’s heart rate is found to be > 100 bpm they are said to be…

A

tachycardic

62
Q

What are two effects of vagal stimulation on heart excitation?

A

1) Slows heart rate
2) Increases AV nodal delay

63
Q

What is the post-synaptic parasympathetic neurotransmitter for the heart?

Which receptor does it act on?

A

Acetylcholine

M2 muscarinic receptor

64
Q

Which drug is used to treat patients with extreme bradycardia and why is it effective?

A

Atropine

Competitive inhibitor of acetylcholine, reducing vagal bradycardia

65
Q

Vagal stimulation decreases the frequency of action potentials - why?

A

It causes the pacemaker cell to hyperpolarise, so it takes longer to reach the same threshold potential to trigger an action potential

66
Q

Vagal stimulation reduces the heart rate, so it is said to have a ___ chronotropic effect on the heart.

A

negative

67
Q

Which parts of the heart are supplied by sympathetic nerves?

A

AV node

SA node

(to increase heart rate)

Myocardium

(to increase force of contraction)

68
Q

What are the three effects of sympathetic stimulation on the heart?

A

1) Increases heart rate
2) Decreases AV nodal delay

(so the opposite of parasympathetic stimulation)

3) Increases force of contraction

(note that parasympathetics have NO EFFECT on contractility)

69
Q

What is the post-synaptic sympathetic neurotransmitter for the heart?

Which receptor does it act on?

A

Noradrenaline

ß1 adrenoceptors

70
Q

Sympathetic stimulation increases the frequency of action potentials - why?

A

Pacemaker cell depolarises, so it reaches threshold potential quicker, so more action potentials occur and heart rate increases

71
Q

What is an electrocardiogram (ECG)?

A

“A record of depolarisation and repolarisation cycles of cardiac muscle obtained from the skin surface”

Graph of heart’s electrical activity which can be used to diagnose disease

72
Q

___ tone dominates under resting conditions.

A

Vagal

to keep the heart rate between 60 - 100 bpm

73
Q

As it increases heart rate, sympathetic stimulation has a ___ chronotropic effect on the heart.

A

positive

Cardiovascular Week 1 & 2 2016/17 (19 decks)

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