2.2 Cardiac Electrophysiology

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2.2 Cardiac Electrophysiology
2015-02-22 20:46:13

Cardiac Electrophysiology
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  1. Skeletal muscle) long cells
    Long cells are bundled together in fascicles
  2. Skeletal muscle) independent (2)
    Independently innervates & contracts
  3. Skeletal muscle) striated
    Because of overlapping of thick & thin filaments
  4. Skeletal muscle) contractile
    It can shorten or lengthen
  5. Skeletal muscle) T-tubule & S.R
    Well developed T-tubule & sarcoplasmic reticulum system that is used for communication between nerve & muscle cell innervated by Somatic N.S
  6. Smooth muscle ) small cells connected by gap junctions
    Small cells connected by gap junctions so neighboring cells can communicate with one another
  7. Smooth muscle ) Non-striated
    They are no striated, they have a smooth tecture
  8. Smooth muscle ) no t-tubules and SR less developed
    • No t-tubules & SR less developed
    • *they do receive innervation but usually by ANS
  9. Cardiac muscle) consists of fibers...
    Arranged in bundles
  10. Cardiac muscle) how many planes does cardiac muscle cover?
    • 3 planes
    • *XYZ
  11. Cardiac muscle) what does the contraction do?
    Squeezes blood out
  12. Cardiac muscle) why is it significant that the cardiac muscle covers 3 planes?
    It allows the heart to contract in different directions to get the blood out
  13. Types of cells of cardiac muscle) Contractile cells: description (3)


  14. Types of cells of cardiac muscle) Contractile cells: T-tubules & SR & triads (2)
    It has some t-tubules & SR

    No triads
  15. Types of cells of cardiac muscle) Contractile cells: where do the t-tubules arrive?
    At the level of the Z-line not at A-I junction (like the skeletal muscle)
  16. Types of cells of cardiac muscle) Contractile cells: general contraction
    • Similar to skeletal muscle
    • ***look it up to review ***
  17. Types of cells of cardiac muscle) Contractile cells: mitochondria
    It contains extensive amounts of mitochondria which is important bc you do not want the heart to fatigue at all during exercise or resting
  18. Types of cells of cardiac muscle) Pacemaker cells: description (3)


  19. Types of cells of cardiac muscle) Pacemaker cells: do these contract?
  20. Communication between cardiac cells) how do they communicate?
    All cells are connected by intercalated discs (gap junctions) reinforced by desmosomes
  21. What do desmosomes do?
    Resist torsion to help cells not to pull apart when contractions occur
  22. Intercalated discs found between (3)


  23. Side note on the way each skeletal muscle cell is innervated
    It is innervates by a particular nerve & receive signal to contract from the specific nerve
  24. Main function of heart
    pump blood
  25. How does heart pump blood?
    Performed by sequential contraction and relaxation of musculature which causes blood to be pushed out of chambers (during contraction) and to fill chambers (during relaxation).
  26. Excitation contraction coupling: steps (4)
    1. Excitation initiated by P.M cells then spreads out

    2. Excites contractile cells which will initiate

    3. Cross bridge formation & contraction thus

    4. Shorten sarcomeres and blood is pumped out
  27. Cardiac AP) what initiates it?
    Pacemaker cells
  28. Cardiac AP) what's embedded in each pacemaker cells (3)
    -leaky Na channels

    -fast CA channels

    -K channels
  29. Cardiac AP) Leaky Na channels
    • They are always open
    • *concentration outside of cell is higher than inside
    • **maintained by Na/K ATPase
  30. Electrical events of pacemaker cells) (5) steps
    • 1. Leaky Na channels causes depolarization
    • *Na keeps coming in causes depolarization

    2. Opening of fast CA channels to depolarize the cell further

    • 3. Calcium channels close at peak depolarization
    • *at around 0 mV

    4. Potassium channels open

    5. repolarization to -55-60 mV

    ***continuous process***
  31. Electrical events of contractile cells) what 3 channels do contractile cells have embedded in their plasma membrane
    -fast Na channels

    -slow CA channels

    -K channels
  32. Electrical events of contractile cells) which 2 ions flow through intercalated discs from other cells?
    CA and Na
  33. Electrical events of contractile cells) steps (6)
    1. Na leaking in from neighboring cells opens fast Na channels

    2. Na channels close rapidly and depolarization causes

    • 3. Slow CA channels to open
    • *open and close slowly
    • **when they open it allows CA to enter the cell & keep cell depolarize so there's enough time for cross bridge to be formed & for contraction of heart muscle to begin

    • 4. K permeability decreases
    • *short time

    5. Increase K and decrease CA permeability

    6. Contraction of cell occurs after AP thru cross bridge formation
  34. Location, sequence of events, PM cells: Sinoatrial node (2)
    -70-75 bpm

    -sets heart rate of the cell
  35. Location, sequence of events, PM cells: Atrioventicular node
    -50 bpm
  36. Location, sequence of events, PM cells: where is SA node located
    Inside RA
  37. Location, sequence of events, PM cells: SA node does 70-75 bpm meaning
    PM cells depolarize at 70-75 bpi on average
  38. Location, sequence of events, PM cells: how do SA node pump 70-75 times?
    Leaky channels causes depolarization at around this pace every time
  39. Do SA node & AV node connect?
    They do not connect rather they have contractile cells between them which is how they communicate with one another
  40. Location, sequence of events, PM cells: AV bundle (3)
    -connects with AV node

    -it beats 30 bpm

    -extends to join with L&R bundle branch
  41. Location, sequence of events, PM cells:L & R bundle branch
    These extend down to apex of heart where they begin to divide off into perkinje fibers
  42. Location, sequence of events, PM cells: Perkinje cells
    -extend into inter-ventricular walls of heart & contractile cells
  43. What happens if SA node is damahged>
    AV node would take over
  44. What's EKG?
    Electrokardio graph
  45. What is EKG
    graphic representation of electrical activity of heart
  46. What are 5 components of EKG
    -isoelectric line




    -ST segment
  47. ekg) isoelectric line
    • Represents point in which cells are at rest
    • * -55-60
  48. ekg) P wave (2)
    -atrial depolarization

    - occurs in atria b/c SA nose is in there
  49. ekg) QRS
    • Represents depolarization of the ventricles
    • *perkinje fibers delivering it to the walls
  50. ekg) T-wave
    • Ventricular repolarization
    • *phase in which cell is getting ready for next AP
    • **Kicks out K while preventing NA from coming out
  51. ekg) ST segment
    Alteration here signifies abnormal AP conduction
  52. ekg) where is atrial repolarization
    During ventricular are depolarizing so its overridden by it on the graph
  53. ekg) Arrhythmias: Bradycardia
    • Slow heartbeat
    • *below 60 bpm
    • **athletes usually have a pulse below 60 but considered healthy because their hearts are so efficient
  54. ekg) Arrhythmias: tachycardia
    • Fast heart beat
    • *above 100 at rest
  55. ekg) Arrhythmias: ectopic focus
    Particular cell in heart will take over the heartbeat so that cell will dictate the heart pulse by using its own
  56. ekg) Arrhythmias: PVC (1+2)
    Premature ventricular contraction

    • -type of ectopic focus
    • -spontaneous not regularly
    • *too much coffee can precipitate this
  57. ekg) Arrhythmias: Fibrillation
    • Uncoordinated contraction of heart meaning all contractile cells are firing in an uncoordinated way
    • *ventricular fibrillation: death
    • *atrial fibrillation: can live with it
  58. ekg) Arrhythmias: heart block (1+3)
    Blockage between SA node & AV node due to AV node being damaged so current doesn't travel all the way, heart attack, or genetic problem.
  59. Normal modification of heart rate) Sympathetic
    Increases heart rate
  60. Normal modification of heart rate) parasympathetic
    Decreases heart rate
  61. Normal modification of heart rate) what would happen if they were removed?
    • We would have no discreet control over heart so difficulty functioning well
    • *slow heart during run
    • *fast heartbeat during sleep