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Cardiovascular > Origin and Conduction of Cardiac Impulse > Flashcards

Origin and Conduction of Cardiac Impulse Flashcards

1
Q

Autorhythmicity

A

The can heart beat rhythmically without any external stimuli

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2
Q

Where does excitation of the heart normally originate?

A

The pacemaker cells of the SAN

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3
Q

Sinus rhythm

A

When the heart is controlled by the SAN

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4
Q

What generates regular spontaneous pacemaker potentials?

A

The cells in the SAN, which have no stable resting membrane potential;

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5
Q

What does the spontaneous pacemaker potential do?

A

Takes the membrane to a threshold, thus creating an action potential

This results in regular spontaneous action potentials in the SAN cells

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6
Q

Define pacemaker potential

A

Slow depolarisation of membrane potential to a threshold

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7
Q

what generates the pacemaker potential?

A

Decrease in K+ efflux
Na+ influx (If)
Transient Ca2+ influx (T-type Ca2+ channels)

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8
Q

Rising phase of pacemaker action potential

A

Depolarisation caused by activation of L-type Ca2+ channels once threshold is reached

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9
Q

Result of rising phase of pacemaker AP being reached

A

Ca2+ influx

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10
Q

Falling Phase of pacemaker Action Potential

A

Repolarisation, resulting in K+ efflux

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11
Q

what causes falling phase of pacemaker action potential?

A

Inactivation of L-type Ca2+ channels and activation of K+ channels

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12
Q

Spread of excitation across heart

A

SAN->AVN->Bundle of His->L+R branches of bundle->Purkinje fibres

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13
Q

How does cell to cell spread of excitation occur from SAN to AVN?

A

Via gap junctions

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14
Q

Where is the only point of electrical contact between atria and ventricles?

A

AVN

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15
Q

Why is conduction in AVN delayed?

A

It allows atrial systole to precede ventricular systole

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16
Q

What allows rapid spread of action potential to ventricles?

A

Bundle of His, its branches and purkinje fibres

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17
Q

Resting membrane potential on atrial and ventricular myocytes

A

-90mV

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18
Q

Cause of rising phase of contraction cardiac muscle cell AP (phase 0)

A

Fast Na+ influx, causing membrane potential to reverse to 20mV

19
Q

Phase 1 of ventricular muscle AP

A

Na+ channels close; transient K+ efflux

20
Q

Phase 2 of ventricular muscle AP

A

Plateau phase

Ca2+ influx

21
Q

Phase 3 of ventricular muscle AP

A

Ca2+ channels close; K+ efflux

22
Q

Phase 4 of ventricular muscle AP

A

Resting membrane potential

23
Q

What causes plateau phase/ phase 2?

A

Influx of Ca2+ through L-type Ca2+ channels

24
Q

Main influence of heart rate

A

Autonomic Nervous system

25
Q

Which nerve continuously influences SAN under resting conditions?

A

Vagus (parasympathetic) nerve

26
Q

Role of vagal tone

A

Reduces intrinsic HR from around 100bpm to about 70bpm

27
Q

What does the vagus nerve supply?

A

SAN and AVN

28
Q

Neurotransmitter for vagus nerve and which receptor it acts on

A

Acetyl Choline

M2 muscarinic receptors

29
Q

Competitive inhibitor of Acetyl Choline, used in extreme cases of bradycardia

A

Atropine

30
Q

Effect of vagal stimulation on threshold, slope of PMP, frequency of AP and +/-ve chronotropic effect

A

Longer to reach threshold
slope decreases
frequency of AP decreases
-ve chronotropic effect

31
Q

What do cardiac sympathetic nerves supply?

A

SAN
AVN
Myocardium

32
Q

Neurotransmitter for cardiac sympathetic nerve and which receptor it acts on

A

Noradrenaline

B1-ADR

33
Q

Effect of sympathetic stimulation on threshold, slope of PMP, frequency of AP and +/-ve chronotropic effect

A

Threshold reached quicker
Slope increases
Frequency of AP increases
+ve chronotropic effect

34
Q

ECG

A

Recording of depolarisation and depolarisation cycle of cardiac muscles taken from skin surface

35
Q

What does LI connect in a 12 lead ECG?

A

RA-LA

36
Q

What does LII connect in a 12 lead ECG?

A

RA-LL

37
Q

What does LIII connect in a 12 lead ECG?

A

LA-LL

38
Q

What does the P wave represent?

A

Atrial depolarisation

39
Q

What does the QRS complex represent?

A

Ventricle depolarisation (masks atrial repolarisation)

40
Q

What does the T wave represent?

A

Ventricular repolarisation

41
Q

What does the PR interval represent?

A

Largely AVN delay

42
Q

What does the ST segment represent?

A

Ventricular systole

43
Q

What does the TP interval represent?

A

Diastole

Cardiovascular (14 decks)

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