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Physiology > Cardiac Electrical > Flashcards

Cardiac Electrical Flashcards

1
Q

Contractile cells

A

Cardiomyocytes

make up bulk of the atrial and ventricular tissue

“work horses”

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2
Q

Conductile cells

A
  • Specialized cardiomyocytes whose sole purpose is to generate and propagate electril activity and spread it throughout
    • SA node
    • Atrial internodal tracts
    • AV node
    • Bundle of His
    • Bundle Branches
    • Purkinje fibers
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3
Q

Cardiomyocytes info:

A
  • striated- Dark bands (myosin) light bands (no myosin)
  • 50-100 uM long: shorter and thinner than skeletal
  • 1-3 nuclei
  • reduced SR system for Ca++ but extensive T-tubule system
  • Desmasomes (macula adherens)- mechanical coupling
  • Gap junctions- electrical coupling
  • one capillary per myocyte
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4
Q

Pathway of electrical excitation

A
  1. SA node (normal pacemaker)
  2. Atrial internodal fibers (atrial kick)-causes Atrial contraction
  3. AV node- delayed to allow atrium to empty completely
  4. AV bundle- Bundle of His
  5. Right and Left Bundle Branches
  6. Purkinje fibers- spreads rapidly causing ventricle contraction
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5
Q

Normal pacemaker of heart

A

SA node

≈100/min

Gets slowed to resting rate by autonomic nervous system

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6
Q

SA node is connected to AV node by…..

A
  • Atrial Internodal pathway
    • specialized conducting cells
    • ≈50 msec
    • stimulus passed to contractile cells which spread it across BOTH atria
    • Stops at atria because myocardium of atria and ventricles are not connected.
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7
Q

Overdrive suppression

A
  • faster firing of SA node suppresses the other cells from acting as pacemakers
  • AV node paces at 40 bpm
  • Perkinjie fibers pace at 20 bpm
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8
Q

Bundle of His

A
  • divides into left and right bundle branches
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9
Q

Perkinje Fibers

A
  • fires first only if SA and AV node dont fire
  • larger cells
  • fast conduction
  • moves upward from apex toward base, effect is to push blood upward
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10
Q

Cardiomyocyte Action Potential

A
  • Phase 0: Depolarization
    • threshold -75 mV
    • Na channel open–Na influx
    • partial closing of K channels
  • Phase 1: early Repolarization (Na/Ca pump goes backwards here)
    • Na channels close
    • K efflux
  • Phase 2: Planeau
    • Ca channels open
    • Ca influx
  • Phase 3: Repolarization
    • Ca channels close
    • K channels fully open, efflux of K
  • Phase 4: Diastole
    • K leak channels remain open
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11
Q

How does Digoxin work?

A
  • Digoxin inhibits Na/K pump which stops Na from leaving.
  • This causes Na to not want to enter via the Na/Ca pump so Ca will build up inside the cell.
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12
Q

Which way does the Na/Ca pump pump?

A

3 Na in

1 Ca out

Leaving cell net +1

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13
Q

How does the absolute refractory period in heart muscle differ from the absolute refractory period in skeletal muscle.

A
  • the cardiac absolute refractory period is much longer than in skeletal muscle.
    • This prevents tetanic contractions (tetany).
    • Also prevents an ectopic pacemaker from stimulating contraction
    • Allows time for ventricle to fill
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14
Q

How does Ca++ level increase in the cardiomyocyte cytosol?

A
  1. Calcium enters myocyte via the L-Type calcium channels
  2. This calcium binds to the ryanodine receptors on SR and stimulates release of Ca++ from the SR
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15
Q

How is the Ca++ removed from the cardiomyocyte cytosol?

A
  1. Ca++ pumped back into the SR by the SERCA pump
    1. 1 atp = 1 Ca++ back into SR
  2. Calcium sent out to ECF via the Na/Ca exchanger
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16
Q

Action potential of the SA node

A
  • Phase 4- pacemaker potential
    • Na channels open “Funny Current”
    • K channels closed
    • upward drift of membrane potential
  • Phase 0- depolarization
    • Voltage gated Ca+ channels open
    • Large influx of Ca+
  • Phase 3- Repolarization
    • Voltage gated Ca+ channels close
    • Influx of Ca stops
    • Voltage gated K channels open
    • efflux of K
17
Q

How does the Autonomic nervous system regulate the SA node?

A
  • Sympathetic Regulation:
    • Beta-1 receptors/ Norepi
      • cause opening of Na and Ca channels and influx of Na and Ca
      • increase steepness of pacemaker potential- + chronotropic effect
  • Parasympathetic Regulation:
    • Muscarinic receptors/ ACh
      • opening of K channels
      • efflux of K
      • hyperpolarizes cell and decreases steepness of pacemaker potential
      • longer time for SA node to reach threshold and - chronotropic effect
18
Q

what part of ekg gets shortened when heart rate increases?

A

diastole

T wave to P wave

19
Q

Normal P wave measurement

A

Atrial depolarization

0.08-0.10 sec

20
Q

Normal QRS complex measurement

A

Ventricular depolarization

0.06-0.10 sec

21
Q

Normal P-R intermal

A

Atrial depolarization plus AV nodal delay

0.12-0.20 seconds

22
Q

Normal Q-T interval

A

Length of depolarization plus repolarization

*Corresponds to action potential duration

0.20-0.40 seconds

Physiology (31 decks)

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