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CRRAB Week 1 - WLB > Cardiac Muscle - Nordgren > Flashcards

Cardiac Muscle - Nordgren Flashcards

1
Q

What are the three ways that cardiac action potentials differ from skeletal muscle action potentials?

A
  1. Self-generating
  2. Conducted directly from cell to cell
  3. Long duration (long refractory period)
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2
Q

What are the three most important ions in the determination of cardiac transmembrane potential?

A
  1. Sodium (Na+) - interstitial fluid
  2. Calcium (Ca2+) - interstitial fluid
  3. Potassium (K+) - intracellular fluid
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3
Q

What changes electrical potential in cardiac muscle?

A
  • Current flowing (movement of ions) through the cell membrane
    • rate of change is proportional to NET current
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4
Q

What is the electrochemical basis of membrane potentials?

A
  • Concentrations differences
    • e.g. high [K+] inside cell –> K+ leaves
  • Electrical potentials
    • e.g. Negative inside cell –> K+ enters
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5
Q

What is the normal equilibrium potential value of K+?

A

-90mV

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6
Q

What is the normal equilibrium potential value of Na+?

A

+60 mV

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7
Q

How do the three states of ion channels (open, closed, inactive) determine membrane ion permeability?

A

Membrane’s permeability = the NET STATUS of the ion channels.

(e.g. “high permeability to Na+ –> many of the Na+ ion channels are open)

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8
Q

How do Activation Gates respond to membrane depolarization?

A

open QUICKLY

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9
Q

How do Inactivation Gates respond to membrane depolarization?

A

close SLOWLY

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10
Q

In general, what do action potentials in myocardial Contractile Cells look like?

A
  • APs similar to those of neurons and skeletal muscle
    • “Fast Response” or “Depolarization Party”
    • 4-0-1-2-3
    • Resting membrane potential (4) = -90mV
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11
Q

In general, what do action potentials in myocardial Pacemaker (Autorhythmic) Cells look like?

A
  • Generate APs spontaneously due to unstable membrane potential
  • “Slow Response”
  • Slower/unstable initial depolarization
  • 4-0-3-4
    • no plateau
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12
Q

What are the five phases of myocardial Contractile Cells?

A
  • 4 = RMP around -90mV
    • Na+ channels open
    • K+ channels (inward rectifier) close
  • 0 = rapid depolarization
    • Na+ influx
  • 1 = initial repolarization
    • Na+ channels close
    • Fast K+ channels (transient outward) open causing K+ influx
  • 2 = plateau (almost net 0 movement)
    • K+ channels close
    • Ca2+ channels (slow inward) open
  • 3 = rapid repolarization
    • ​Slow K+ channels (delayed rectifier) open causing K+ efflux
    • Ca2+ channels close
  • 4 = return to RMP
    • K+ channels (delayed rectifier) close
    • K+ channels (inward rectifier) open causing influx of K+
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13
Q

What are the four phases of myocardial Pacemaker Cells?

A
  • 4 = slow/unstable depolarization
    • funny channels open
      • large Na+ influx
      • small K+ efflux
    • transient Ca2+ channel opens
      • small Ca+ influx
  • 0 = rapid depolarization
    • long-lasting Ca2+ channel opens
      • huge Ca2+ influx
  • 3 = rapid repolarization
    • K+ channel opens
      • large K+ efflux
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14
Q

What are the main differences in AP between the contractile and the pacemaker cells?

A
  • Phase 4:
    • RMP vs. unstable pacemaker potential
  • Phase 0:
    • mediated by Na+ in contractile cells
    • mediated by Ca2+ in pacemaker cells
  • Phase 1 & 2:
    • absent in pacemaker cells
  • Phase 3:
    • no difference
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15
Q

Why/How does the AV node slow transmission of the action potential signal?

A
  • Determined by # of gap jxns in the intercalated discs
    • fewer gap jxns = slower
  • AV node has fewer gap junctions that the SA node and atrial myocardium.
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16
Q

What does the T-wave on an electrocardiogram represent?

A

Ventricular repolarization

17
Q

What does the P-wave on an electrocardiogram represent?

A

Atrial depolarization

18
Q

What does the R-wave on an electrocardiogram represent?

A

Ventricular depolarization

19
Q

What does the PR interval on an electrocardiogram represent?

A

Conduction time through atria & AV node

20
Q

What does the QT interval on an electrocardiogram represent?

A

Total duration of ventricular systole (contraction)

21
Q

What does the ST segment on an electrocardiogram represent?

A

plateau phase of ventricular APs

22
Q

What major cardiac event is missing from an electrocardiogram? Why?

A
  • Atrial Repolarization
    • masked by large R-wave
    • larger tissue –> large depolarization wave
23
Q

How does acetylcholine slow the heart rate?

A
  • Increases permeability of resting membrane to K+
  • Decreases diastolic current through funny channels (Na+influx/K+efflux)
    • prolongs time to depolarization
24
Q

How does norepinephrine increase the heart rate?

A
  • Increase diastolic inward currents through funny channels
    • shortens time to depolarization
25
Q

Why is calcium necessary for muscular contraction?

A

Calcium displaces tropomyosin, and binds to troponin to iniate contraction.

Ca2+ allows actin & myosin to interact, causing contraction.

26
Q

What is the difference between preload and afterload?

A
  • Preload:
    • passive/resting tension placed on cardiac muscle cells before contraction
      • fxn of the volume and pressure at end of diastole
  • Afterload:
    • active tension placed on cardiac muscle cells during contraction
      • fxn of resistance the left ventricle must overcome to circulate blood
27
Q

Summarize the Law of LaPlace? What does it mean/imply?

A
  • The total ventricular wall tension (T) depends on both intraventricular pressure (P) and the internal ventricular radius (r).
    • T = P x r
  • Implication:
    • easier for muscle cells to produce adequate internal pressure at end of ejection (small radius) than beginning of ejection (large radius)
28
Q

What is Isometric Contraction?

A
  • “Fixed Length”
    • ends of muscle held rigidly
  • AV valves close –> SL valves open
29
Q

What is Isotonic Contraction?

A
  • “Fixed Tension”
    • Activation of unrestrained muscle (not fixed length)
    • causes it to shorten without force because it has nothing to develop force against
30
Q

What is the Inotropic state?

A

Altered cardiac activity due to an agent or substance

(e.g. ACh, NE)

31
Q

What are the refractory periods of the cardiac cell electrical cycle?

A
  • Contractile cells
    • Phase 0 - Phase 3
    • From rapid depol –> plateau –> rapid repol
  • Pacemaker cells
    • Phase 0 + Phase 3
    • From rapid depol –> rapid repol
  • Cells are in absolute refractory state during most of the AP
    • cannot be stimulated for another firing
    • precludes summated or tetanic contractions
32
Q

What is the normal pathway of action potential (electrical) conduction through the heart?

A
  1. SA Node (right atrium)
  2. Left atrium (Bachmann’s Bundle)
  3. AV Node
  4. Bundle of His (Atrioventricular Bundle)
  5. Right/Left Ventricles (Bundle Branches)
  6. Purkinje fibers
33
Q

How do cardiac parasympathetic nerves alter the heart rate and conduction of cardiac action potentials?

A

Parasympathetic (ACh/Vagus Nerve) –> Slow HR

“Negative Chronotropic Effect”

(hyperpolarize RMP)

34
Q

How do cardiac sympathetic nerves alter the heart rate and conduction of cardiac action potentials?

A

Sympathetic (NE) –> Increase HR

“Positive Chronotropic Effect”

(shortens time to depolarization)

35
Q

What are the sub cellular structures responsible for cardiac muscle cell contraction?

A
  • Intercalated Disks
    • end of two adjacent cells
  • Fascia Adherens
    • anchoring site of actin
  • Macula Adherens (Desmosome)
    • bind intermediate filaments
  • Gap Junctions
    • channels formed of connexin
    • facilitate transmission of electrical impulse
36
Q

Briefly describe the excitation-contraction process?

(Hint: Ca2+)

A
  • AP enters
  • VG-Ca2+ channels open
  • Ca2+ influx
  • Ryanodine receptor channels release Ca2+
  • Ca2+ SPARK
  • Ca2+ displaces tropomyosin & binds troponin
  • Actin/Myosin change conformation which initiates contraction
  • Ca2+ unbinds from troponin –> Relaxation
  • Ca2+ pumped back out (exchanged with Na+)
  • Na+ pumped out, K+ in via Na/K ATPase

CRRAB Week 1 - WLB (11 decks)

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