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Histology - Exam 2 > Exam 2 - Muscle > Flashcards

Exam 2 - Muscle Flashcards

1
Q

epimysium

A

outermost layer of dense CT surrounding muscle

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2
Q

perimysium

A

CT surrounding muscle fascicles

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3
Q

contents of muscle fiber bundles

A

individual multinucleated muscle fibers/cells 10-100 um wide and up to 30 cm long

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4
Q

endomysium

A

basal lamina and reticular fibers that surround individual muscle cells - contains capillaries that supply blood to fibers

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5
Q

location of nuclei in skeletal muscle cells

A

in periphery just beneath sarcolemma

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6
Q

satellite cells

A

infrequent small stem cells found b/w the sarcolemma and basal lamina that may proliferate after trauma to form new myoblasts

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7
Q

triad system

A

T-tubules + sarcoplasmic reticulum; located at junction of A and I bands

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8
Q

T-tubules

A

infolding of plasma membrane, forms inner portion of triad

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9
Q

sarcoplasmic reticulum

A

modified sER, forms two side portions of triad

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10
Q

motor end plate

A

myoneural jxn - interaction site b/w nerve axon and muscle where basal lamina of axon and teloglia fuse w/ muscle fiber

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11
Q

changes in axon as it nears muscle cell

A

loses myelin sheath, but Schwann cells remain

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12
Q

teloglia

A

name for Schwann cells in the motor end plate region

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13
Q

what happens in synaptic cleft?

A

Ach from axon terminals diffuses across cleft and binds to Ach receptors located in junctional folds/subneural clefts of sarcolemma

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14
Q

number of muscle fibers innervated by one axon?

A

one or more

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15
Q

motor unit

A

a nerve and the muscles it innervates

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16
Q

botulism toxin

A

binds to presynaptic membrane, blocking Ach release

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17
Q

curare

A

paralytic drug that binds to Ach receptor

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18
Q

myasthenia gravis

A

autoantibodies against Ach receptors that block Ach binding and lead to progressive muscle weakness

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19
Q

mechanism of contraction

A

AP along sarcolemma-> T-tubules -> release Ca from terminal cisternae of SR -> Tn-c moves tropomyosin -> ATP on myosin hydrolyzed -> myosin binds actin -> Pi released -> head flexed -> ADP released -> actin pulled into A band -> new ATP binds myosin, releases myosin from actin

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20
Q

red fibers

A

type I fibers - slow twitch: high Mb, high mitochondria, fatigue resistant (stain strongly b/c mito enzymes)

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21
Q

white fibers

A

type II fibers - fast twitch: low Mb, low mitochondria, more stored glycogen, higher myosin-ATPase activity

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22
Q

intermediate fibers

A

characteristics b/w type I and II

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23
Q

control of fiber type differentiation

A

by innervation - red may become white by denervating and replacing with nerve from white fiber

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24
Q

muscle spindles

A

stretch receptors in perimysium that regulate muscle tone and tension - run parallel w/ main muscle and contain intrafusal fibers and neuron terminals in a fluid filled CT capsule

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25
Q

muscle spindle nerve terminal discharge rate

A

discharge rate increases as the sensory ending is stretched

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26
Q

types of intrafusal fibers

A

nuclear bag (cluster of nuclei) or nuclear chain

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27
Q

types of spindle nerve terminal endings

A
  • annulospiral (wind around intrafusal fibers)
  • flower spray (terminate in clusters)
  • Gamma-efferents/fusimotor (motor end plats formed near spindle poles)
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28
Q

induction of satellite cell proliferation

A

after muscle injury, myoD transcription factor and JGF (hepatocyte growth factor) induce proliferatoin of these cells

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29
Q

side-population cells

A

cells that can differentiate into all major blood cell lineages

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30
Q

where do you find side-population cells?

A

bone marrow and skeletal muscle

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31
Q

rigor mortis

A

death -> PM more permeable to Ca -> cross bridge attachment -> muscle fibers contract while Ach and ATP present -> once ATP used up, actin and myosin stay linked until decomposition

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32
Q

muscle atrophy

A

due to disuse - reduction in muscle fiber size, NOT number

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33
Q

myofilaments

A

make up myofibrils

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34
Q

thin myofilaments

A

actin, tropomyosin, troponin

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35
Q

thick myofilaments

A

myosin

36
Q

A band

A

anisotropic band - thick and thin filaments, but only place thick filaments are found

37
Q

I band

A

isotropic band - thin filaments only, bisected by Z disk where thin filaments attach

38
Q

H band

A

contains myosin w/o heads and creatine kinase

39
Q

creatine kinase

A

catalyzes ATP formation from ADP and phosphocreatine

40
Q

M line

A

region of myomesin linking w/ myosin

41
Q

Z disk

A

attachment point for thin filaments - contains alpha-actinin

42
Q

sarcomere

A

functional unit of contraction

43
Q

myofilament related structural proteins (7)

A
  • titin
  • nebulin
  • alpha-actinin
  • myomesin
  • desmin
  • dystrophin
  • C protein
44
Q

titin

A

elastic protein that connects myosin to Z disk - acts like spring to keep myosin filaments centered in sarcomere

45
Q

nebulin

A

inelastic protein attached to Z disk that runs parallel to actin

46
Q

myomesin

A

myosin binding protein that holds myosin filaments in register at M line

47
Q

C protein

A

myosin binding protein similar to myomesin

48
Q

alpha-actinin

A

bundles actin filaments into parallel arrays and anchors them to Z disk

49
Q

desmin

A

intermediate filament that helps bind myofibrils to each other and encircles Z disk - linked to each other by plectin

50
Q

dystrophin

A

actin binding protein that reinforces and stabilizes sarcolemma during contraction by linking cytoskeleton w/ ECM

51
Q

actin

A

2 strings (F actin) of monomers (G actin) wrapped around each other in right-handed helix 7 nm in diameter

52
Q

what regulates polymerization of actin in vivo?

A

thymosin B4 and profilin

53
Q

what regulates actin filament length, stability/turnover?

A

cofilin, severin, gelsolin, villin, CapZ, gCAP39

54
Q

tropomyosin

A

elongated protein dimer (35K MW) that lies in groove of actin helix and binds 3 troponin peptides

55
Q

Tn-T

A

binds Tn complex to tropomyosin

56
Q

Tn-I

A

inhibits binding of actin to myosin w/ help of tropomyosin

57
Q

Tn-C

A

binds Ca, releasing Tn-I-tropomyosin inhibition of actin activation of myosin ATPase

58
Q

alphabeta-crystallin

A

HSP that protects desmin from stress-induced damage

59
Q

Duchenne’s muscular dystrophy

A

X chromosome linked mutation in dystrophin gene that disrupts sarcolemma and Ca entrance into cell, resulting in muscle fiber necrosis

60
Q

sarcoglycanopathies

A

limb-girdle muscular dystrophies with mutations in sarcoglycan genes - disrupts interactions w/ other proteins and association of sarcolemma with ECM

61
Q

myosin

A

both a globular and fibrous structural protein w/ 2 heavy chains and 4 light chains

62
Q

how many myosin molecules are thick filaments made of?

A

300-400

63
Q

what does proteolytic digestion do to myosin molecules?

A

cleaves each heavy chain to produce a head and a tail

64
Q

how many light chains does each head bind?

A

two light chains

65
Q

heavy meromyosin

A

globular head of the heavy chain of myosin that contains an ATP and actin binding region

66
Q

light meromyosin

A

rodlike alpha-helical tail of the heavy chain of myosin

67
Q

cardiac muscle characteristics

A

banding, single nucleus/cell that is more centrally located, each fiber = many cells joined by intercalated discs, branched fibers

68
Q

size of cardiac muscle cells

A

100-150 um long x 10-20 um wide

69
Q

intercalated discs

A

transverse portion w/ fasciae adherens (actin filament anchor site) and macula adherens to bind adjacent cells together; lateral portion w/ gap junctions that ionically couple adjacent cells

70
Q

how is cardiac muscle different from skeletal muscle?

A
  • more mitochondria
  • more extrafibrillar sarcoplasm
  • larger T tubules
  • T tubules at Z disk
  • diads instead of triads
  • don’t regenerate
  • intra and extracellular Ca
  • heals w/ fibrous CT that can block conduction
71
Q

phospholamban

A

controls active transport of Ca into SR lumen

72
Q

appearance of cardiocytes after MI

A

24 hrs: eosinophilic cytoplasm w/ some pyknotic nuclei

3 days: inflammatory cells infiltrate tissue

73
Q

smooth muscle

A

muscle under involuntary control of sympathetic or parasympathetic NS

74
Q

smooth muscle cells

A
  • spindle shaped
  • may branch
  • 20 um long
  • single central oval nucleus w/ 1 or more nucleoli -surrounded by basal lamina
  • caveolae on PM
  • cytoplasmic dense bodies w/ a-actinin (fxnal = of Z disk)
  • staggered arrangement of cells
  • no sarcomeres
75
Q

what might smooth muscle cells secrete?

A

collagen and elastin

76
Q

what does smooth muscle cytoplasm contain?

A

bundles of 5-7 nm thin filaments (actin, tropomyosin ONLY); 8-10 nm intermediate filaments (desmin, vimentin); 12-16 nm thick filaments (myosin)

77
Q

myoepithelial cells of ectodermal origin

A

single, basket shaped smooth muscle cells found around sweat, salivary, lacrimal, and mammary glands

78
Q

what attachments do myoepithelial cells contain?

A

hemidesmosomes

79
Q

what do myoepithelial cells in mammary glands and lacrimal glands contract in response to, respectively?

A

oxytocin and Ach - to help dispel contents of glands

80
Q

smooth muscle of mesodermal origin

A

located in respiratory, circulatory, digestive, reproductive tracts

81
Q

smooth muscle of ectodermal origin

A

located in iris and ciliary body of eye

82
Q

smooth muscle intermediate filament expression? why?

A

at high levels - serve as links in cytoskeletal network b/w dense bodies

83
Q

smooth muscle myosin

A

2 heavy and 4 light chains, but filaments form only under certain conditions - dephosphorylation -> completely soluble

84
Q

smooth muscle contraction

A

stim -> Ca increase in cytoplasm -> complex w/ calmodulin -> activate MLCK -> phosphorylate myosin -> myoson unfolds, forms filaments -> allows myosin to interact w/ actin

85
Q

what other small molecule may also activate MLCK?

A

cAMP

86
Q

how does estrogen influence smooth muscle?

A

increases cAMP -> contraction of smooth muscle

87
Q

how does progesterone influence smooth muscle?

A

decreases cAMP -> relaxation of smooth muscle

Histology - Exam 2 (6 decks)

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