1. What is the hierarchy of muscle cell organization?
    myofilament > myofibril > muscle fiber/cell > muscle fascicle
  2. What are myofibrils?
    series of sarcomeres linked together like "beads on a string", align w/ bands above and below
  3. What is another name for muscle fiber?
    • muscle cell
    • multinuc w/ eccentric nuc
  4. What is skeletal muscle derived from?
    paraxial mesoderm (forms somites) and somitomeres in developing head of embryoblast
  5. neuromuscular junction
    ends of nerve endings interact w/ muscle fibers at motor end plates
  6. What are characteristics of skeletal muscle?
    • multinuc, eccentric nuc
    • long fibers (but not as long as muscle itself)
    • voluntary control (innervated by cholinergic nerve endings)
    • contraction results from shortening sarcomeres
  7. What are the ends of muscle fibers attached to?
    CT w/in muscle or CT tendons at each end of muscle
  8. What is the isotropic band?
    • (I band) "monorefringent"- plane of polarized light is not bent
    • light in color
    • bisected by Z disc
    • made of only thin actin filaments
  9. What is the anisotropic band?
    • (A band) birefringent: plane of polarized light is bent
    • made of thick and thin filaments (depends on your XS as to what the composition is)
  10. What is the Hensen band?
    • (H band); thick filaments only
    • btw thin filaments of A band; at center of A band
  11. What is the M line?
    made of only thick myosin filaments w/ cross connections of myomesin
  12. What is the Z disk?
    bisects I band
  13. What is a sarcomere?
    area btw 2 Z disks; basic contractile unit of striated muscle
  14. What composes actin filaments?
    • G actin monomers that comprise filamentous F actin
    • two F actins intertwine to form a helix
  15. What is the purpose of tropomyosin?
    occupies shallow grooves btw actin helices; masks myosin-binding sites on G actin
  16. What is the purpose of troponin?
    • located on tropomyosin molecules; 3 subunits:
    • troponin T: binds troponin to tropomyosin
    • troponin C: binds Ca2+ which causes conformational change in tropomyosin and exposure of myosin binding site on G actin
    • troponin I: binds to actin to prevent actin-myosin interaction
  17. What is the structure of myosin?
    • two globular heads on two helices that intertwine
    • heads have ATPase activity
  18. What is myomesin?
    holds myosins together
  19. What is titin?
    connects ends of myosin molecules to Z line
  20. What is the sarcoplasmic reticulum?
    sER in muscle cells; stores intracellular Ca2+ and release
  21. What is sarcolemma?
    cell membrane of striated muscle cells
  22. What are transverse tubules?
    invaginations of sarcolemma into interior of muscle fiber; occur at A-I junction in skeletal muscle and Z-intercalated disk in cardiac muscle
  23. sarcoglycans
    aka TM prots
  24. congenital muscular dystrophies
    gene mut or deletion in lamins of dystroglycans
  25. oculopharyngeal muscular dystrophy
    due to mut in Type 1 red muscle fibers
  26. myasthenia gravis
    due to mut in type 2 white fibers
  27. autosomal limb girdle muscular dystrophies
    gene mut or deletion in sarcoglyans
  28. What are terminal cisternae?
    • cisternae of sarcoplasmic reticulum which parallel T tubule
    • two, one for each side of T tubule; forms a triad in skeletal muscle and diad in cardiac muscle
  29. How do terminal cisternae function?
    have Ca2+ stored in it, released after deplolarization from AP; Ca2+ causes troponin to relieve tropomyosin inhibition
  30. Where are terminal cisternae located?
    at A-I junction; v closely assoc w/ myofibrils for best contraction
  31. How are sER and calcium related?
    release calcium once receives signal and re-uptakes calcium right after releasing it so that contractions do not continue to happen
  32. When does rigor occur?
    if levels of Ca2+ become too high or ATP levels become depleted (actin and myosin become cross-linked)
  33. How are actin filaments anchored?
    via dystrophin protein to TM proteins that are linked to basal lamina; maintains muscle integrity during contraction

    dystrophin is lg prot so lots of chances for mutations (duschennes and beckers)
  34. Red fibers (type 1)
    • lots of myoglobin and oxidative enz
    • -"slow twitch", sustained force, weight-bearing, enduring
    • -sm diameter
    • -NADH dk staining (bc of myoglobin)
    • -abundant lipids
    • -minimal glycogen
    • -one motor neuron innervates many muscle fibers (less precise control)
    • -located in limb muscles and long back muscles
  35. White fibers (type 2)
    • -"fast twitch", sudden movements; purposeful motion; easily fatigued
    • -less myoglobin
    • -NADH light staining
    • -minimal lipids
    • -abundant glycogen
    • -few mit
    • -one motor neuron innervates few muscle cells (precise control)
    • -located in extraocular muscles, digits
  36. What does endomysium surround?
    ind myocytes
  37. What does perimysium surround?
    bundles of muscle cells (fascicles)
  38. What does epimysium surround?
    entire muscle; many fascicles
  39. What is the nt for skeletal muscle?
    Ach; uses cholinergic (nicotinic) receptors
  40. How does the motor unit work for skeletal muscle?
    multipolar neuron from ventral horn of gray column synapses on ind fibers (motor end plate)
  41. What are some characteristics of muscle fibers and nerves?
    • bundle of skeletal muscle fiber innervated by single motor neuron
    • myelinated
    • every muscle fiber receives a nerve terminal
  42. How do skeletal muscle cells regenerate?
    stem cells--->myoblasts--->new muscle fibers
  43. How can you tell an original muscle cell from new muscle cell?
    new cell has a more central nuc (bc from myoblast) whereas an original cell has an eccentric nuc
  44. Where are cardiac muscle nuclei located?
    centrally; mononucleated
  45. How do cardiac muscle cells contract?
    same as skeletal muscle cells
  46. What is an intercalated disk?
    junctional complex that connects sequential cardiocytes; creates lots of attachment and communication sites for gap junctions
  47. What are components of intercalated disks?
    • maculae adherens (desmosomes)-attachment of intF
    • fascia adherens-attachment of actin thin filaments
    • gap junctions-ion transport to synchronize heart contraction
  48. What is an intracellular bridge?
    bridge between layers of cardiocytes; allows heart to contract at once
  49. What is the function of mit in cardiocytes?
    elongated around the myofibrils; lots bc need lots ATP for heart
  50. What does the sarcoplasmic reticulum look like in cardiocytes?
    less well-developed; diads; located at Z disks (but not intercalated disks)
  51. What else is in cardiocytes?
    • lots of cytoplasmic glycogen
    • secretory granules in atria contain ANP
  52. What is the function of ANP in cardiocytes?
    • when the atria is stretched (bc of too much H20), cardiocytes in atria release ANP:
    • osmotic balance
    • distention atrial wall
    • stimulates diuresis (counters ADH)
    • relaxes cardio channels
  53. What are purkinje fibers?
    • modified cardiocytes; lgr than regular cardiocytes w/ central nuc and less myofibrils peripherally located
    • binucleate; lots of glycogen granules
  54. Where are purkinje fibers located?
  55. How are purkinje fibers organized?
    nodes and bundles
  56. What is the function of purkinje fibers?
    to facilitate conduction of contractile stimulus (not actually contract as skeletal...more of a transmitter to rest of heart)
  57. How are cardiac muscle cells regenerated?
    replaced w/ fibrous CT
  58. What do smooth muscle cells look like?
    • organized as bundles or sheets of cells
    • spindle shaped
    • involuntary control
    • non-striated
    • stains "frosty pink" color
    • organelles (golgi and sec granules) around each end of nuc
  59. What can smooth muscle cells secrete?
    • elastin (tunica media cells of elastic arteries)
    • type 4 and 3 collagen (tunica intima cells of blood vessels)
    • lamin and proteoglycans (CTs)
    • renin (juxtaglomerular cells in kidneys)
  60. How do smooth muscles utilize gap junctions?
    to act synchronously
  61. How are smooth muscles innervated?
    • nonmyelinated, ANS
    • no specialized synapse
    • only a few cells are innervated
    • has gap junctions to allow concerted contractions
  62. What are interstitial cells of Cajal?
    (ICC): highly specialized pacemaker cells that modulate autonomic stimulation of smooth muscle cells and are important in frequency of rhythmic contraction (i.e. peristalsis)
  63. How do smooth muscles contract?
    • sliding filament mechanism w/ actin-myosin
    • Ca2+ dep
  64. What does Ca2+ do for smooth muscle contraction?
    Ca2+ induces calmodulin dep act of myosin light chain kinase...initiates actin-myosin interaction
  65. What are some characteristics of smooth muscle contraction?
    • slow
    • contractions are sustained (little ATP req)
  66. How do smooth muscles regenerate?
    undergo mitosis
  67. What is the conducting pathway of the heart?
  68. What is the parasympathetic innervation of the heart?
    vagus nerve-slows down heart contraction
  69. What is the sympathetic innervation of the heart?
    • speeds up contraction at SA
    • stim cardiac muscle cells to contract harder
    • goes to each node and cell
  70. What is variscosity?
    bare nerve terminal of smooth muscle cells where NE is dumped onto
Card Set
MS1/Mod 1: histology: muscle