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Block 2 Week 1 > HIST - Muscle > Flashcards

HIST - Muscle Flashcards

1
Q

THREE TYPES OF MUSCLE

A

Skeletal Muscle (SkM)

  • Striated, multinucleated
  • Elongated nuclei lie along the periphery
  • In a cross section, cells look angular

Cardiac Muscle (CM)

  • Striated
  • Intercalated discs
  • Uni/multinucleated, lie in center

Smooth Muscle (SM)

  • No striations
  • Elongated, fusiform cells
  • One, centrally located nucleus per cell
  • Density depends on amount of extracellular CT
  • Cross-section = Highly cellular
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2
Q

CHARACTERISTICS OF ALL MUSCLE

A
  • All muscle is derived from primitive mesenchymal cells of the mesoderm
    • EXCEPT the iris –> derived from the ectoderm
  • All muscle cells have microfilaments: actin and/or myosin
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3
Q

GROWTH OF SKELETAL MUSCLE

A
  • Muscle cells grow unorganized during embryogenesis
  • Become oganized into fibers later (by unnamed proteins)
  • **myoblasts **fuse to form myotubes which form a mature muscle that can act as syncytium
  • Breakdown:
    • Muscle
      • Fasicles
        • Muscle fibers (cells)
          • Myofibrils
            • Myofilaments
              • Actin/myosin
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4
Q

ORGANIZATION OF SKELETAL MUSCLE

A

Surrounded by CT sheaths that

  1. Allow transmission of force
  2. Allow tranmission of nerves and vasculature
  3. Sarcolemma = PM, around cell/fiber
    • Endomysium = around each muscle fiber
      • Perimysium = around fasicle
        • Epimysium = around muscle
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5
Q

SKELETAL MUSCLE FACTS

A
  1. # of muscle fibers fixed at puberty b/c myostatin inhibits new fiber development
  2. Myostatin = cytokine produced by muscle cells
    • Circulates as a hormone after puberty (12-14 y/o)
    • Regulates muscle development
      • inhibits myoblast differentiation and hypertrophy
    • Athletes/strong people often have mutant myostatin
    • Many ilicit drugs inhibit myostatin
  3. Satellite cells = muscle progenitor cells
    • Differentiate into myoblasts
    • Function in new muscle fiber growth until puberty (12-14 y/o)
    • Function in injury muscle
  4. Can regenerate (ish)
    • Trauma –> fibrosis (fibroblasts replace dead SkM with CT)
  5. Hypertrophy = increased in muscle fiber size
    • Caused by repeated exercise
  6. **Hyperplasia **= increase in number of fibers
    • May be induced by stressful exercise (weight lifting)

Muscle growth from exercise = increase in size of fibers and increase in CT surrounding fibers

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6
Q

SARCOMERE

A
  • Banding
    • Z line to Z-line = sarcomere = functional unit of SkM
    • I band = actin, thin; isotropic (allows polarized light); 7 nm
    • A band = myosin, thick, and actin; anisotropic properties from myosin; 15 nm
    • H band = myosin
  • Muscle fiber = repeating units of sarcomeres
  • T-tubule = triad
    • Invagination + SR (smooth ER) on either side
    • Ca2+ release and storage from SR’s terminal cisternae
  • Sliding filament model
    • I and H bands shorten
    • A bands unchanged
    • Z discs move closer
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7
Q

SKELETAL MUSCLE CONTRACTION

A
  • Voluntary, by nerve innervation at motor end plate
    • Capped by a Schwann cell (protects)
    • Synaptic cleft = neuromuscular junction
  • Stimulated by ACh
    • All or none rule
  • Ca2+ release regulates contraction
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8
Q

CARDIAC MUSCLE

A
  1. Striated
  2. Intercalated discs
  3. 1-2 centrally located nuclei
  4. Bifurcating and anastomosing
  5. Atrial granules = vesicles that secrete ANP
    • Atrial naturetic peptide = acts on the kidney to regulate BP by changing sodium/water reabsorption
  • ​Heart contraction occurs in a wringing motion from atria to ventricles
  • Cannot regenerate
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9
Q

ORGANIZATION OF CARDIAC MUSCLE

A
  • Endocardium (epithelial cells)
    • Myocardium (CM)
      • Epicardium/visceral pericardium (mesothelium)
        • Secretes pericardial fluid into the pericardial cavity
          • Parietal pericardium (mesothelium) (Also secretes pericardial fluid)
  • CS –> cardiac tamponade, increase in fluid, pressure on ventricles
    • Causes irregular contractions
  • T-tubule = diad
    • ​Invagination + SR network
    • Ca2+ storage and release
    • No cisternae
    • TONS of mitochondria in CM
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10
Q

TYPES OF CARDIAC CELLS

A

CARDIOCYTES

  • Contractile cardiomyocytes = CM
  • Nodal cardiocytes = SA, AV nodes
  • **Myoendocrine cardiocytes **= in atria, secrete ANP
  • Purkinje fibers = conduct from AV node
    • ​Derived from cardiomyocytes (have straitions)
    • Lie directly under endocardium
    • Full of glycogen
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11
Q

INTERCALATED DISCS

A
  • Step-like arrangement of CM fibers
  • Vertical = FA (specialized ZA) and MA (desmosomes)
  • Horizontal = GJs
  • Function: help CM act in syncytium
  • ​Contraction = spontaneous; involuntary
    • ​Internal pacemaker
    • Modulated by ANS
    • Rhythmic, all-or-none
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12
Q

SMOOTH MUSCLE

A
  1. Relaxed = elongated, fusiform
  2. Contracted = corkscrew
  3. Have cytoplasmic dense bodies/plaques (sarcolemma) = Z discs
  4. Actin and myosin myofilaments
  5. No striations
  6. External basal lamina
  7. GJs (LOTS of them)
  8. No T-tubules –> caveolae = Ca2+ storage and release
  9. One, central nucleus per cell
  10. Involuntary contractions, modulated by ANS
    1. ​Parasympathetic/Sympathetic ANS
    2. Hormones (ex: oxytocin)
    3. Drugs
  11. Cross-section =
    1. ​Inner circular layer
    2. Outer longitudinal layer
  12. Can regenerate
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13
Q

SMOOTH MUSCLE CONTRACTION

A
  • Cytoplasmic dense bodies/plaques are pulled together by myofilaments
  • Crumples into a ball
  • Isotonic contraction
  • Not “all-or-none” can be partial
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14
Q

SMOOTH MUSCLE CLASSIFICATION

A
  • Single Unit
    • ​Can contract individually
    • Act in syncytium
    • Ex: intesine, urethra, ureter
  • Multi Unit
    • ​Can contract individually because each has its own innervation.
    • Not one nerve to one cell, but each cell is stimulated by a nerve, not by other cells
      • ​Via **en passant **axonal swellings/projections into each muscle fiber = motor end plate
      • One nerve can innervate many SM cells
    • Ex: iris, trachea, esophagus
  • Vascular
    • ​Blood vessels
    • Mix of single and multi unit properties
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Block 2 Week 1 (8 decks)

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