Muscle

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Author:
mnm2186
ID:
29085
Filename:
Muscle
Updated:
2010-08-07 15:40:35
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Histology
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Exam 1
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  1. Characteristics of skeletal muscle
    striated

    long parallel arrangement

    multiple peripheral nuclei
  2. Characteristics of cardiac muscle
    striated w/ intercalated discs

    branched cells

    central nucleus
  3. Characteristics of smooth muscle
    non-striated

    fusiform (tapering at both ends)

    central "cork screw" nucleus
  4. What is the only voluntary muscle type?
    skeletal muscle
  5. Development of skeletal muscle cell
    • Immature myoblasts eventually fuse to form multinucleated muscle fibers (muscle cell)
    • - each muscle cell is surrounded by a basal lamina

    • Myoblasts that do not fuse are called satellite cells
    • - play a minor role in muscle regeneration
  6. Connective tissue of skeletal muscle fibers
    • Endomysium – CT surrounding individual muscle cells
    • - composed of reticular fibers and external lamina (basal lamina)

    • Perimysium – thicker CT that surrounds and defines fascicles
    • - functional bundles of muscle fibers; visible to naked eye

    • Epimysium – dense CT that surrounds the entire muscle (collection of fascicles)
    • - Investing fascia of gross anatomy
  7. Reflexive contraction
    Involuntary contractions
  8. Tonic contraction
    slight contraction that gives muscle firmness (assisting stability of joints and posture)
  9. Isometric contraction
    Muscle length does not change
  10. Concentric isotonic contraction
    Muscle length changes

    Contracting muscle shortens during movement
  11. Eccentric isotonic contraction
    Muscle length changes

    • Contracting muscle lengthens during movement
    • (lowering an object / squatting down)
  12. How are skeletal muscle fiber types characterized?
    Speed of contraction / metabolic activity

    • ATPase enzymatic velocity
    • Myoglobin content
    • Mitochondrial number
  13. Type I Muscle Fiber
    • Red / slow twitch / slow oxidative
    • not easily fatigued (postural / endurance muscles)

    • High myoglobin content
    • Many mitochondria (high in oxidative enzymes)
    • Slow myosin ATPase reaction velocity
  14. Where are type I muscle fibers found?
    • Predominate in the deep back muscles and other postural muscles
    • (maintain upright posture)

    Soleus muscle of the calf
  15. Type IIb Muscle Fiber
    • White / fast twitch / fast glycolytic
    • powerful rapid contraction (easily fatigued)

    • Low myoglobin content
    • Few mitochondria (low in oxidative enzymes)
    • Very fast myosin ATPase reaction velocity
  16. Where are type IIb muscle fibers found?
    Extraoccular eye muscles
  17. Type IIa Muscle Fiber
    • Intermediate / fast oxidative glycolytic
    • Make up fast twitch fatigue resistant motor units
  18. Order from largest to smallest:
    Myofilaments / Fascicles / Myofibrils / Fibers
    • Fascicles are collections of fibers bound by a perimysium
    • Fibers are collections of myofibrils (extend the entire length of cell)
    • Myofibrils are composed of myofilaments
    • Myofilaments are subdivided into thick (myosin) and thin (actin) filaments
  19. Types of myofilaments
    • Thick filaments - Myosin (2 Heavy chains + 2 Pairs of Light chains)
    • Heavy chain tails aggregate forming thick filaments
    • Heavy chain globular head has binding sites for actin & ATP)

    • Thin filaments - Actin (F-actin)
    • F-actin = double helix of globular monomers (G-actin)
  20. Tropomyosin
    Long thin molecule that wraps around the actin filaments (bind in F-actin groove)
  21. Troponin
    Troponin is complex of three subunits

    • TnT - binds to tropomyosin
    • TnC - binds to calcium ions
    • TnI - inhibits the actin-myosin interaction
  22. Describe the different muscle bands
  23. Functional unit of skeletal muscle
    • Sarcomere
    • (region between two Z lines)
  24. Filaments in the I-band
    Actin (thin) filaments only
  25. Filaments in the A-band
    Overlapping myosin (thick) and actin (thin) filaments
  26. Filaments in the H-band
    Myosin (thick) filaments only
  27. Structure of Z-line and M-line
    Z-line: where actin (thin) filaments are bound together by alpha-actin (found in smooth muscle)

    M-line: where adjacent myosin (thick) filaments are linked (center of H-band)
  28. Skeletal Muscle Contraction Cycle
    • 1. Attachment (rigor): myosin is bound to actin
    • 2. Release: myosin is uncoupled from actin and binds ATP
    • 3. Bending: ATP hydrolysis causes myosin head to bend and advance

    4. Force Generation: myosin binds to actin and returns to its original conformation – forcing movement of the thin filament along the thick filament (ADP is lost)

    5. Reattachment: cycle can repeat
  29. Sliding filament model
    Thin filaments (actin) slide past thick filaments (myosin)

    • I-bands / H-bands shorten
    • Sarcomere shortens (Z-lines are drawn closer)
    • A-band does not change in length
  30. Role of calcium in skeletal muscle contraction
    • Low [Ca+] (Calcium is being pumped back into SR)
    • - myosin binding site on actin is blocked

    • High [Ca+]
    • - Calcium binds to TnC
    • - Conformational change breaks TnI-actin bond
    • - Tropomyosin moves (no longer blocking binding site on actin)
  31. Sarcoplasmic Reticulum
    Specialized network of endoplasmic reticulum around myofibrils

    Actively transports Ca2+ back into cisternae after contraction
  32. Skeletal Muscle Triad
    Triad = SR-TT-SR @ the A-I junction
  33. Function of T-tubules
    Rapidly spread depolarization thru muscle fiber (widespread release of Ca2+ from the SR)

    • This allows for uniform contraction of the muscle fiber
    • - voltage gated Ca+ channels open
  34. Muscle Spindle
    Stretch receptor (rate and duration sensitive)

    • Has a CT capsule and intrafusal muscle fibers
    • (skeletal m. fibers producing force for movement are extrafusal fibers)

    Has both afferent and efferent innervation

    Anchored to perimysium and endomysium of extrafusal fibers
  35. Deep Tendon Reflex
    • Rapid tap of the tendon causes a rapid stretch of the muscle spindle
    • (Initiates monosynaptic deep tendon reflex)
  36. Intercalated Discs
    Form end-to-end attachment between cardiac myocytes

    • Macula adherens
    • Zonula adherens
    • Gap junctions
  37. Cardiac Muscle Diad
    Diad = SR & T-tubule
  38. T-tubules:
    • - larger than in skeletal m.
    • - located at Z-line (not the A-I junction)
    • - large mitochondria span distance between T-tubules
  39. How do cardiac cells have spontaneous contraction?
    Purkinje Fibers

    • few myofibrils
    • form gap junctions with cardiac m. cells
    • no intercalated disks
    • large pale cells (abundant mitochondria)
  40. Major intermediate filament protein in smooth muscle
    Desmin
  41. Ca2+ binding protein in smooth muscle
    Calmodulin!

    (no troponin)
  42. Smooth Muscle Contraction
    Slow prolonged contraction (initiated by ANS)

    caldesmon / calponin are actin binding site proteins that block the binding site on myosin

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