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ZZZZ Pathophysiology (B) > Week 12 lec - Skeletal muscle pathology > Flashcards

Week 12 lec - Skeletal muscle pathology Flashcards

1
Q

what percentage of a healthy person’s body is muscle?

A

40%

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2
Q

Skeletal muscle consists of what 4 things?

A
  1. Muscle tissue
  2. Connective tissue
  3. Nerve and blood supply
  4. Satellite cells
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3
Q

what are the 3 connective tissue layers in skeletal muscle?

A

3 connective tissue layers:

  1. Epimysium – tough outer layer gives shape (large collagen bundles).
  2. Perimysium - surrounds bundles (fascicles) of myofibres (loose CT – BV).
  3. Endomysium - encloses individual myofibres (fine collagen fibres).
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4
Q

what is the diameter of a muscle fibre in an adult?

A

50μm

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5
Q

what causes the striated appearance in skeletal muscle?

A

A band, I band, Z line

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6
Q

what does a motor unit consist of?

A

a single motor neuron and all the myofibres it innervates (2-2000)

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7
Q

in humans, how many motor units does each muscle contain?

A

hundreds

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8
Q

in terms of skeletal muscle plasticity, what 3 changes can occur?

A
  • Hypertrophy
  • Atrophy
  • Regeneration
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9
Q

what is the term used to describe a degenerative loss of skeletal muscle?

A

sarcopenia

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10
Q

what are satellite cells?

A

muscle specific stem cells (the precursor for a muscle cell)

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11
Q

what do satellite cells do?

A

Facilitate post-natal muscle growth and regeneration

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12
Q

where do satellite cells normally reside?

A

between the sarcolemma and basement membrane

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13
Q

in what state are satellite cells normally in?

A

quiescent state

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14
Q

what causes satellite cells to activate, proliferate, differentiate and fuse into myofibres?

A

injury or resistance exercise

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15
Q

how can you tell th difference between a satellite cell and muscle cell nucleus?

A
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16
Q

what does all postnatal muscle growth depend on?

A

the activation, proliferation and fusion of satellite cells with existing myofibres

17
Q

what happens to the protein to DNA ratio of the myofibre during hypertrophy?

A

it stays the same due to fusion of satellite cells

18
Q

how does skeletal muscle adapt to an increase in workload?

A

by increasing the size and amount of contractile proteins within the sarcomeres of each myofibre

19
Q

what endogenous or exogenous hormones can trigger hypertrophy?

A
  1. Insulin-like growth factor-1 (IGF-1)
  2. growth hormone (GH)
  3. anabolic steroids.
20
Q

what are the 4 steps of hypertrophy?

A
  1. Resistance exercise, physiological loading, testosterone or enhanced nutrition
  2. Activation, proliferation and subsequent fusion of satellite cells with existing myofibres
  3. Increase in the amount of contractile proteins within each myofibre. Protein synthesis > protein degradation. Increase mitochondrial content.
  4. Increase in the size and diameter (CSA) of individual myofibres. Increase in associated muscle strength (force production) Increase fatigue resistance
21
Q

what are the benefits of using anabolic steroids?

A
  • Increase muscle mass
  • High levels of peak power and strength
  • Increase RBC count, aid in recovery
  • Increase determination and aggression

Male testosterone about 25x higher than females so females have a lot more to gain by using it

22
Q
A
  • Tendons susceptible to injury
  • CVS, liver, kidney problems, CM fibrosis, BP
  • Reduced LH and FSH concentrations = Reduced / inhibited gametogenesis = Male and female infertility – due to suppression of HPA axis
23
Q

what biochemical and enzymatic responses are responsible for muscle atrophy?

A

the reduced capacity to synthesize new protein and the up-regulation of pathways leading to increased protein breakdown (e.g. ubiquitin pathway)

24
Q

factors which cause atrophy?

A
  • ageing (sarcopenia)
  • disuse (immobilisation)
  • denervation
  • inflammatory conditions associated with cancer (cachexia), burns and anorexia/starvation
25
Q

3 steps of atrophy

A
  1. Aging (sarcopenia), disuse (immobilisation), denervation, cachexia, burns and anorexia/starvation
  2. Decrease in the amount of contractile proteins within each myofibre Protein degradation > protein synthesis
  3. Reduction in the size and diameter of individual myofibres. Decreased force production and lower fatigue resistance
26
Q

Causes of myofibre necrosis?

A
  1. disease (polymyositis, muscular dystrophies)
  2. eccentric exercise
  3. irradiation
  4. ischemia
  5. direct trauma (crush, cut, tear)
  6. transplantation (grafting)
  7. thermal injury or biological toxins (venom, streptococcus A, toxoplasma)
27
Q

what is the aim of skeletal muscle regeneration?

A

to prevent the loss of muscle mass

28
Q

what are the 7 steps that occur in the first 7 days of regeneration, starting with damage leading to necrosis?

A

1) damage leads to myofibre necrosis
2) Inflammation and phagocytosis
3) hyper-contraction of myofibrils
4) revascularisation
5) activation and proliferation of satellite cells 6) fusion of myoblasts into myotubes
7) re-innervation

after that growth and maturation continues

29
Q

what’s the difference in nuclei location between a newly formed myoblast and a mature myoblast?

A

nuclei is central in new myoblasts

30
Q

what are the markers for the activation stage of myogenesis?

A

Pax7 is the main marker

CD34, Myf5, Beta-gal and some Myob are also markers of that stage

31
Q

what are the markers for the proliferative stage of myogenesis?

A

Myf5 and Beta-gal are the main players

Pax7, and some MyoD are also markers of that stage

32
Q

what are the markers of the commitment to differentiation stage of myogenesis?

A

MyoD is the main player

Myf5, Beta-gal myogenin and a small amount of Pax7 are also markers of that stage

33
Q

what are the markers of the fusion to myotube stage of myogenesis?

A
34
Q

what are the markers of the maturation into myofibre stage of myogenesis?

A
35
Q
A

ZZZZ Pathophysiology (B) (16 decks)

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