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Anatomy Week 7 > Muscle Histology > Flashcards

Muscle Histology Flashcards

1
Q

Which muscle types are striated (i.e. have alternating dark and light bands)?

A

skeletal and cardiac

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2
Q

What is epimysium?

A

dense irregular CT surrounding the entire muscle

NOTE: most muscles are too large to be sectioned in their entirety and so the epimysium will only occasionally be present in tissue sections

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3
Q

What is the name of the dense irregular CT that divides muscles into fascicles/bundles?

A

Perimysium

[contains collagen fibers, but seem to be ‘empty spaces’]

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4
Q

What tissue type is endomysium and where can it be found?

A

loose CT (delicate)
surrounds individual muscle cells
contains capillaries and nerve fibers

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5
Q

T or F: skeletal muscle cells have a single nucleus located at the periphery of the cell.

A

False, they have multiple nuclei at the cell periphery (i.e. just under the plasma membrane (termed the sarcolemma))

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6
Q

What is the morphology of skeletal muscle cells?

A

long and cylindrical

Called fibers

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7
Q

What are myofibrils, and where can they be found?

A

cylindrical units located in the sarcoplasm (muscle cell cytoplasm) that run the length of the muscle fiber

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8
Q

What are T-tubules?

A

invaginations of the sarcolemma that encircle all of the myofibrils

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9
Q

What is a sarcoplasmic reticulum and what are its contents?

A

Highly elaborated smooth ER that encircles each myofibril and stores calcium

A sarcomere is the basic functional unit of a skeletal muscle fiber

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10
Q

What is contained in the cytoplasm between the myofibrils?

A

mitochondria and glycogen granules (for energy), and sarcoplasmic reticulum

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11
Q

What makes up a myofibril?

A

a chain of sarcomeres

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12
Q

T or F: muscle fibers can be characterized by their alternating light and dark bands

A

T

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13
Q

What forms the boundaries of each sarcomere?

A

z-line

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14
Q

What are thin filaments composed of and where do they insert?

A
  • made of actin

- insert on z-line

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15
Q

What are thick filaments?

A
  • occupy the center of the sarcomere
  • consist of ~250 myosin units
  • bilaterally symmetric and staggered
  • bipolar
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16
Q

T or F: thick filaments contain globular myosin heads on both sides of the sarcomere?

A

T

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17
Q

Describe the relationship between thin and thick filaments?

A
  • parallel
  • interdigitated
  • partly overlapping
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18
Q

What is the A band?

A

dArk band- aka central region were thick filaments (containing myosin) are located

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19
Q

What is the I band?

A

LIght band - central regions where thin (actin) filaments are located

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20
Q

T or F: the A band spans two adjacent sarcomeres?

A

False - the I band does this

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21
Q

What causes then filaments to slide past thick filaments toward the center of the sarcomere?

A

power stroke that results from myosin heads hydrolyzing ATP

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22
Q

T or F: to contract, each of the ~500 myosin heads of the thick filament must hydrolyze and complete the power stroke a few times

A

T

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23
Q

What band shortens in muscle contraction?

A

I band due to increased overlapping of actin and myosin

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24
Q

How does perimysium appear with H and E staining?

A

clear, but it does contain collagen fibers

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25
Q

T or F: all three types of muscle have epimysium and perimysium

A

False; only skeletal muscle has all three layers

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26
Q

T or F: cardiac muscle has endomysium surrounding individual cells.

A

True

Note: smooth muscle has none of the three layers

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27
Q

What is the plasma membrane of the muscle cell called?

A

sarcolemma (cytoplasm = sarcoplasm)

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28
Q

what are cross striations?

A

alternating light and dark bands seen in longitudinal sections of skeletal muscle

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29
Q

What is the m-line?

A

dark line in the Middle of the sarcomere

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30
Q

What does actin bind to in order to attach to the z line?

A

alpha actinin

31
Q

Describe all the the changes that happen to the bands and lines in sarcomere contraction

A
  • more overlap between thick and thin filaments
  • shortening of the I band and H zone
  • NO change in the A band and M line
32
Q

Is the sarcoplasmic reticulum continuous with the T-tubule system or the sarcolemma?

A

NO

33
Q

What is the terminal cisternae?

A

enlarged portion of the SR adjacent to the T-tubules

34
Q

What is a triad?

A

T - tubule + the 2 flanking terminal cisternae

35
Q

What are the steps in voluntary muscle contraction?

A
  1. motorneuron activate, action potential conducted along its axon and into synaptic terminal
  2. acetylcholine released from the synaptic terminal
  3. Ach bind to the Ach receptor on the muscle fiber
  4. AP conducted up and down muscle fiber along the sarcolemma and into the body of the muscle fiber along T-tubules
  5. AP in T-tubules causes Ca2+ release from SR
  6. Ca2+ binds troponin causing tropomyosin to shift position
  7. myosin heads bind to actin, then power stroke and muscle contracts
  8. Ca2+ pumped back into the SR when no longer electronically active
36
Q

T or F: cardiac muscle is striated and contains light and dark bands

A

True, this is the similar to skeletal muscle

37
Q

How many nuclei can be found in a cardiac muscle cell?

A

one

38
Q

Describe the morphology and arrangement of cardiac muscle cells.

A

Short and cylindrical; arranged end to end to form branched fibers joined by intercalated discs

39
Q

What structures found in intercalcated discs?

A
  1. Macula aderens
  2. Gap junctions
  3. Fascia adherens
40
Q

What is the purpose of the macula adherens in cardiac muscle tissue?

A

keeps cells attached despite contraction forces

41
Q

What is the purpose of gap junction in cardiac muscle tissue?

A

coordinate contraction among neighboring cells

42
Q

What is the purpose of the fascia adherins in cardiac muscle tissue?

A

analogous to zonula adherens; thin filaments insert into cytoplasmic plaque (this takes the place of the z-line)

43
Q

What is the major site of Ca2+ influx associated with muscle contraction for cardiac muscle?

A

T-tubules

44
Q

Compare the sarcoplasmic reticulum (SR) of muscle tissue in the heart to that in the skeletal muscle.

A
  • not as well developed as in skeletal muscle

- does NOT have LARGE terminal cisternae

45
Q

What is a diads?

A

profile of T-tubule + SR

46
Q

Describe the nucleation and morphology of smooth muscle.

A
  • spindle shaped
  • one centrally-located nucleus
  • much smaller than skeletal muscle
47
Q

How is smooth muscle arranged in hollow visceral organs?

A

typically 2-3 layers oriented longitudinally or circularly

48
Q

Which of the following can be found in smooth muscle?

a. striations
b. myofibrils
c. light and dark bands
d. sarcomeres
e. thin and thick filaments

A

e. Thin and thick filaments are the only two of these found in smooth muscle

49
Q

How does myosin different in smooth muscle?

A
  • all of the heads in the thick filaments face the same direction (unipolar as opposed to bipolar)
  • myosin heads must be phosphorylated for contraction to occur
50
Q

Describe the arrangement and relative ratio of thin and thick filaments in smooth muscle.

A
  • thin filaments insert into alpha-actinin located in dense bodies
  • dense bodies form an anastomosing network throughout the cytoplasm
  • many more thin filaments than thick filaments
51
Q

What triggers smooth muscle contraction and what happens once triggered?

A
  • an increase in cytosolic Ca2+ conc. initiates contraction via the Ca2+ regulated phosphorylation of myosin
  • nucleus shortens and becomes passively pleated due to the spatial arrangement of the dense bodies and thin and thick filaments
52
Q

Rank the following by most well developed sarcoplasmic reticulum to the least.

A

skeletal mus. > Cadiac mus. > Smooth mus.

53
Q

Does smooth muscle contain gap juctions?

A

yes, this allows them to coordinate contraction

54
Q

Does smooth muscle contain T-tubules?

A

NO

55
Q

Where are vesicles located in smooth muscle?

A

under sarcolemma

56
Q

What determines the length and diameter of sarcomeres found in skeletal muscle?

A

Length - determined by properties of its constituent molecules

Diameter - constraints based on the rate of Ca2+ diffusion

57
Q

T or F: sarcomeres in skeletal muscle are very uniform in size

A

T

58
Q

What happens in skeletal muscle when myofibrils grow beyond an optimal diameter or length?

A

diameter - It splits into two myofibrils

length - sarcomeres are added to their ends

59
Q

What protein attaches to myosin thick filaments at the M line?

A

myomesin

60
Q

What is the job of titin in muscle fibers?

A
  • Extends from Z line to M line
  • helps to anchor thick filaments
  • provides elasticity to sarcomeres
  • largest known protein (~4000 kD)
61
Q

Why are muscle fiber multi-nucleated?

A

They originate from dividing uni-nucleated myoblasts that have fused together

NOTE: Fusion results in a losing the capacity to divide

62
Q

Where are satellite cells located in skeletal muscle, what special properties do these have in muscle?

A
  • Adjacent to the skeletal muscle fiber UNDER the basal lamina surrounding the fiber
  • They have very limited regenerative capacity
63
Q

Can the basal lamina be seen using a light microscope?

A

NO

64
Q

What links actin to the muscle cell membrane (sarcolemma) and to the basal lamina?

A
  • Actin is linked by dystrophin
  • dystrophin linked to dytroglycan
  • dystroglycan complex links to basal lamina
65
Q

What causes muscular dystrophy?

A
  • mutations in genes coding for dystrophin, dystroglycan, or sarcoglycan
  • these proteins that allow for appropriate linkage which is needed for maintaining structural and functional integrity of muscle fibers
66
Q

What is the most common type of muscular dystrophy?

A

Duchenne

67
Q

What is the difference between Becker and Duchenne muscular dystrophy at the molecular and clinical level?

A
  • Duchenne - caused by a small deletion in the dystrophin gene that SHIFTS the READING FRAME
  • this leads to a lack of protein function and a more severe clinical manifestation
  • Becker - caused by a large deletion in the dystrophin gene that does NOT result in a frame shift
68
Q

What demonstrates early pathology of Duchenne muscular dystrophy in a tissue sample?

A
  • degenerated muscle fibers
  • some fibers are regenerated (these are small)
  • Variation in size of the muscle fibers
  • Increased amount of endomysium

Note: each of these characteristics becomes more defined as the disease progresses

69
Q

What is the basis of exon skipping therapies for Duchenne muscular dystrophy (DMD)?

A
  • you skipped the mutated exon that causes the frame shift that causes DMD
  • This leads to a protein that is missing chunks but still folds properly like the proteins in Becker Muscular Dystrophy
70
Q

How is cardiac muscle typically repaired by the body in adults?

A

Its repaired by proliferating fibroblasts and growth of CT to make scar tissue

71
Q

How can cardiac muscle in a child be repaired?

A
  • cardiomyocytes can undergo a final round of DNA synthesis and nuclear division without cell division (like in muscle cell)
  • This leads to binucleation of ~25% of cardiomyocytes
72
Q

What two non-cardiac cell types have demonstrated the capacity to repair cardiac tissue?

A

Mesenchymal Stem Cells

Induced Pluripotent stem cells

73
Q

T or F: Smooth muscle cells retain the ability to proliferate into adulthood.

A

True - however, this is NOT done through satellite stem cells

Anatomy Week 7 (7 decks)

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