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human physiology and pharmacology > the cardiac action potential and ECG > Flashcards

the cardiac action potential and ECG Flashcards

1
Q

what is autorhythmicity

A

the heart contracting rhythmically as a result of APs it generates itself

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2
Q

what are the two types of specialized cardiac cell

A

Contractile cells (99%; normally do not initiate APs)
Autorhythmic cells (do not contract; initiate or conduct APs)

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3
Q

do cardiac autorhythmic cells have a resting membrane potential

A

no, instead they display pacemaker activity

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4
Q

what is pacemaker potential

A

an autorhythmic cell membranes’ slow drift to threshold

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5
Q

autorhythmic cells cyclically initiate what?

A

APs which then spread through the heart to trigger contraction without any nervous stimulation

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6
Q

special non-contractile cells that demonstrate autorhythmicity are located at 4 specific sites. What are they

A

1)The sinoatrial node
2)The atrioventricular node
3)The bundle of His (atrioventricular bundle)
4)Purkinje fibers

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7
Q

what is the normal pacemaker of the heart

A

sinoatrial node

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8
Q

the cells of the heart are linked electrically, what does this mean

A

the rate of the fastest will be the rate of all

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9
Q

how many APs per min does an atrial and ventricular myocardium normally have

A

0

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10
Q

how can SA node discharge frequency be altered

A

by parasympathetic and sympathetic stimulation

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11
Q

functions of the atrioventricular node

A
  • AV node forms the only conducting pathway between the atrial muscle and Bundle of His and hence the ventricles
    .* AV node introduces a considerable delay to the spread of excitation (~100 ms). This allows time for blood to move from the atria to the ventricles.
  • AV node cells have well-developed latent powers of rhythmicity and can take over pacemaking if impulses from the SA node fail to reach them
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12
Q

what goes in to increase the membrane potential and what goes out

A

Na+ and Ca2+
K+ goes out

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13
Q

The cycle of voltage change across cardiac myocytes occurs in 5 distinct phases

A

1) Depolarization
2) Early repolarisation
3) Plateau phase
4) Late repolarization
5) Resting potential

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14
Q

what happens in the plateau phase of the action potential

A

K+ out fast (slight dip on the graph)
Ca2+ in slow (flattens out a bit)
K+ out fast (drops all the way down on the graph)

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15
Q

at what rate do SA nodes fire APs

A

70-80 APs per min
The rate of firing is regulated by the autonomic nervous system

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16
Q

what links neighboring cardiac muscle cells

A

the presence of gap junctions

17
Q

what do gap junctions do

A

they allow the rapid spread of APs from cell to cell, e.g. an AP originating in the SA spreads throughout both atria, stimulating the simultaneous contraction of R +L atrial muscle

18
Q

what is an ECG (electrocardiogram) the record of

A

the overall spread of electrical activity throughout the heart

19
Q

where the electrodes attach to and why does it work

A

it is attached to the skin and it is able to record the small parts of electrical activity that is able to reach the body surface

20
Q

what are the 3 important points when considering what an ECG represents?

A
  1. An ECG is not a direct recording of the actual electrical activity of the heart.
  2. The ECG is a complex recording representing the overall spread of activity throughout the heart during depolarisation and repolarisation. It is not a recording of a single AP in a single cell at a single point in time.
  3. The recording represents comparisons in voltage detected by electrodes at two different points on the body surface, not the actual potential.
21
Q

what is the specific arrangement of each pair of connections called

A

lead

22
Q

how many leads are there on an ECG and what are the locations on which they record

A

there are 12 leads
6 different arrangments from the limbs
6 chest leads at various sites around the heart

23
Q

what do the 6 limb leads include

A

1
2
3
aVR
aVL
aVF

24
Q

leads 1,2,3,are what type of leads

A

bipolar leads because two recording electrodes are used

25
Q

the electrode placed on the right leg serves as what

A

a ground and is not a recording electrode

26
Q

aVR, aVL, and aVF leads are what type of leads

A

unipolar

27
Q

what does the exploring electrode mainly record

A

the electrical potential of the cardiac musculature immediately beneath the electrode in six different locations surrounding the heart

28
Q

Lead 1=?

A

Right arm and left arm

29
Q

Lead 2=?

A

right arm and left leg

30
Q

Lead 3=?

A

Left arm and left leg

31
Q

explain ECG cycle

A

SA node fires
P wave = atrial depolarization
PR segment = AV nodal delay
QRS complex = ventricular depolarization (atria polarizing simultaneously)
ST segment = time during which ventricles are contracting and emptying
T wave = ventricular repolarization
TP interval = time during which ventricles are relaxing and filling

32
Q

on a normal ecg is a separate wave for atrial repolarisation visible

A

no
the electrical activity associated with atrial repolarisation occurs simultaneously with ventricular depolarisation and is masked by the QRS complex

33
Q

why is the p wave smaller than the QRS complex

A

because the atria have much smaller muscle mass than the ventricles

34
Q

explain the p wave

A

atrial depolarisation moving towards the recording electrode

35
Q

explain the Q wave

A

left to right depolarization of the interventricular septum moving slightly away from the electrode

36
Q

explain the R wave

A

depolarisation of the main ventricular mass moving towards the recording electrode

37
Q

explain the S wave

A

depolarization of ventricles at the base of the heart moving away from the recording electrode

38
Q

explain the t wave

A

ventricular repolarisation moving in a direction opposite to that of the depolarization accounts for the usually observed upward deflection

39
Q

the main thing to happen at the QRS complex???

A

ventricular depolarisation

human physiology and pharmacology (16 decks)

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