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BME 201 > Cardiovascular System - Cardiac Action Potential & Electrocardiogram > Flashcards

Cardiovascular System - Cardiac Action Potential & Electrocardiogram Flashcards

1
Q

cardiac cycle

A

alternating contraction and relaxation of cardiac muscle (myocardium)

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2
Q

cardiac muscle fibers

A
  • smaller/shorter
  • branched ends (connect to each other)
  • one or two nuclei
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3
Q

cardiac muscle tissue (2 components)

A
  • syncytium

- gap junctions

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4
Q

syncytium

A

multinucleate mass of cytoplasm resulting from fusion of cells

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5
Q

gap junctions

A

conduct the action potential to neighbouring cells

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6
Q

cardiac vs skeletal muscle cells

A
  • both striated
  • involuntary vs voluntarily
  • 10-20um diameter vs 20-100um
  • 50-100um in length vs mm to cm in length
  • 1-2 nuclei vs hundreds
  • often branch vs do not branch
  • connect to neighbouring cells vs fuse with tendons
  • many mitochondria vs few
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7
Q

3 types of muscle tissue in myocardium

A
  • atrial muscle
  • ventricular muscle
  • specialized muscle tissue coordinates electrical signals (conduction system of heart)
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8
Q

conduction system of heart

A

“an automatic electrical system controls contraction of heart”

  • sinoatrial (SA) node
  • atrioventricular (AV) node
  • bundle of His
  • bundle branches (right and left)
  • Purkinje fibers
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9
Q

SA node

A

pacemaker

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10
Q

AV node

A

delays transmission of signal

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11
Q

bundle of His and ramifications

A

conducts signal to ventricles

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12
Q

main phases of action potential **

A
  1. resting membrane potential
  2. threshold potential
  3. depolarization
  4. depolarization
  5. hyperpolarization
  6. refractory period
  7. inward and outward currents
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13
Q

heterogeneity of cardiac action potential **

A
  • heart is heterogeneous with respect to cell type
  • these different cells have different versions of their action potential
    (slide 14)
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14
Q

phases of action potential in SA node

A

“SA nodal cells spontaneously generate action potential
0. upstroke/depolarization
1/2. absent
3. pacemaker potential

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15
Q

characteristics of action potential in SA node

A
  • automaticity (spontaneously generate action potentials without neural inputs)
  • unstable resting membrane potential
  • no sustained plateau
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16
Q

effect of ANS stimulation on SA node action potential

A

autonomic nerves affect the heart rate by affecting the pacemaker potential

17
Q

conductance changes and currents in the myocyte and action potential

A
  • upstroke of action potential is due to inward Na+ current
  • phase 1 repolarization is due to an outward K+ current, while Na+ channel inactivates
  • Ca2+ inward current maintains the Plateau of Phase 2
  • Ca2+ channel closure and increased gk repolarize the cell during Phase 3
18
Q

phases of action potential in the atria and ventricles

A
  1. rapid depolarization
  2. partial repolarization
  3. plateau
  4. repolarization
  5. pacemaker potential
19
Q

characteristics of action potential in atria and ventricles

A
  • stable resting membrane potential
  • longer action potential
  • sustained plateau
    “contractile cells do not spontaneously generate action potentials
20
Q

basic principle of ECG

A
  • equivalent electric dipole is produced by heart muscle during repolarization
  • heart muscle fibres act as electric dipoles
21
Q

Einthoven’s triangle

A
  • 3 bipolar leads

- voltage in each lead is the projection of the heart vector onto that lead

22
Q

Normal ECG configuration components

A
  • P wave, PR interval, QRS complex, ST segment, T wave, U wave, QT interval
23
Q

origin of P wave of the ECG

A
  • heart electric dipole varies with time and so does the recording on leads I, II, and III
  • atrial depolarization causes the P wave
24
Q

origin of QRS complex of ECG

A
  • the depolarization of the ventricles occur in a sequential manner
  • ventricular depolarization causes the QRS complex
25
Q

P wave

A

atrial depolarization

26
Q

P-R interval

A

total atrial activity prior to activation of the bundle of His

27
Q

QRS complex

A

ventricular depolarization

28
Q

ST segment

A

time between ventricular depolarization and repolarization

29
Q

T wave

A

ventricular repolarization

30
Q

U wave

A

usually flat or not seen

occurs in electrolyte disturbances, heart diseases

31
Q

QT interval

A

total ventricular activity (QRS complex, ST segment, and T wave)

32
Q

augmented limb leads

A

augmented unipolar limb leads use combinations of only two electrodes for the indifferent electrode

33
Q

sympathetic stimulation of SA node

A
  • shorter time, higher slope of pacemaker potential
34
Q

parasympathetic stimulation of SA node

A
  • longer time, lower slope of pacemaker potential

BME 201 (10 decks)

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