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Y3 Musculoskeletal pathology > Musculoskeletal - Muscles > Flashcards

Musculoskeletal - Muscles Flashcards

1
Q

What is a myocyte?

A

A skeletal fibre

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2
Q

Describe the features of myocytes

A
  • Multinucleated cells
  • Up to 1 meter in length
  • Satellite cells represent the stem component of this tissue
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3
Q

Myocytes are enclosed within?

A

Basal laminae and a thicker layer called the endomysium

  • Endomysium surrounding each myocyte
  • Perimysium surrounding more than one myocyte, keeping them together
  • Epimysium surrounds the whole muscle
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4
Q

Describe a transverse and longitudinally cut section of muscle

A
  • Transverse section: there is a lot of cytoplasm filled with contracted fibres with peripheral nuclei
  • Longitudinally there are very elongated cell nuclei with lots of peripheral nuclei
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5
Q

Which structures are found in the muscle fibre?

A
  • Myofibres
  • Mitochondria
  • Sarcoplasmic reticulum
  • Myoglobin
  • T-tubules
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6
Q

What is the function of the sarcoplasmic reticulum?

A

Storing calcium molecules

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7
Q

Explain how muscle contraction occurs

A

Electrical stimulus at the neuromuscular junction causes the release of calcium from the SR which binds to actin and starts the process of muscle contraction

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8
Q

Which molecule is needed for muscle relaxation?

A

ATP

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9
Q

Where is ATP produced?

A

In the oxidative pathways within the mitochondria

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10
Q

Describe the features of type I muscle fibres

A
  • Slow switch
  • Oxidative
  • Fatigue resistant
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11
Q

Describe the features of type II muscle fibres

A
  • Fast switch
  • Glycolytic
  • Rapidly fatigable
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12
Q

What is rhabdomyolysis?

A

If there is an infectious agent, trauma, etc that hits an area, it is likely that the whole cell wont die, only a part of it

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13
Q

What happens if there is damage to muscle but not enough to cross the basal laminae?

A
  • Macrophages go to the area of damage to remove the necrotic debris
  • Satellite cells join in and differentiate into a myotube, which is the precursor to the myofiber. They can then replace and restore the muscle
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14
Q

What happens if there is damage to muscle that is extensive and destroys a big part of the fibre including the basal laminae?

A

Satellite cells still join in but there is nothing to guide the formation of myotubes so the healing is not back to what it was before and there is much more fibrosis replacing the muscles (can also get some adipose tissue)

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15
Q

What are the causes of muscle atrophy?

A

Lack of use, cachexia, aging, endocrine disorders (Cushing’s), denervation

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16
Q

Describe the gross appearance of muscle atrophy

A

Generalised or Focal: reduction in size of the muscle affected

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17
Q

Describe the histological appearance of muscle atrophy

A

Reduction in size of the myofibres.

Chronically: substitution of the myofibres by fibrous tissue or fat

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18
Q

Which spp/breeds are affected by congenital muscular hypertrophy/

A

Cattle (Blue Belgian) and (Callipyge) Sheep

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19
Q

Congenital muscular hypertrophy occurs due to defects in which gene?

A

Myostatin gene

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20
Q

Describe the gross appearance of congenital muscular hypertrophy

A

Increased size of muscles: Muscle showing most obvious changes are thighs, rump, loin and shoulder

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21
Q

Describe the histological appearance of congenital muscular hypertrophy

A

Increased numbers/size of normal fibres within affected muscle

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22
Q

What is the cause of splayleg?

A

Inherited myofibrillar defect

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23
Q

Splayleg affects which spp?

A

Pigs

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24
Q

Describe the gross appearance of splayleg

A

Neonatal pig, fail to sustain quadrupedal position: splayleg attitude

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25
Q

Describe the histological appearance of splayleg

A

Histologically there is reduced myofiber diameter with decreased myofibrils within muscle fibres and increased cytoplasmic glycogen

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26
Q

Muscular dystrophy affects which spp/breed/gender?

A

'’X-Linked muscular dystrophy” – affecting males

Dog (Golden Retriever and others), Cat

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27
Q

Describe the pathophysiology of muscular dystrophy

A

Caused by defects in the gene coding for Dystrophin, a sarcolemmal associated protein

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28
Q

Describe the gross appearance of muscular dystrophy in:

  • Dogs
  • Cats
A

Dog: Muscular atrophy, pale white streaks in muscles
Cat: Muscular hypertrophy, particularly over the neck and shoulder, oesophagus and diaphragm

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29
Q

Describe the histological appearance of muscular dystrophy in:

  • Dogs
  • Cats
A

Dog: large dark fibres, necrotic fibres (which may be infiltrated by macrophages), regenerate fibres and mineralization
Cat: marked variation in fibre size, with numerous hypertrophied fibres often with internalised nuclei polyphasic necrosis with mineralization and minimal endomysial fibrosis

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30
Q

Which condition is associated with muscular dystrophy in older dogs?

A

Cardiomyopathy

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31
Q

Which spp is affected by malignant hyperthermia

A

Pigs (genetic)

32
Q

Describe the pathophysiology of malignant hyperthermia

A
  • Mutation in the Ryanodine receptor ® dysregulation of excitation-contraction coupling.
  • Characterised by unregulated release of calcium from the sarcoplasmic reticulum.
  • Leads to excessive myofibre contraction and causes a severe increase in body temperature
33
Q

Describe the gross appearance of malignant hyperthermia

A

Animals have pale, soft, wet (exudative) muscles and develop rapid rigor mortis (P.S.E. meat)

34
Q

Describe the histological appearance of malignant hyperthermia

A

Histologically there is oedema and there may be multifocal monophasic injury with hypercontraction.

35
Q

Myasthenia gravis affects which spp?

A

Dogs and cats

36
Q

Describe the two pathophysiology’s of Myasthenia gravis

A

Acquired: circulating autoantibodies against skeletal muscle acetylcholine receptors which leads to a severe decrease in the number of functional receptors
Congenital: Born with defective NMJ’s – larger surface area and a reduced acetylcholine receptor density

37
Q

Describe the gross and histological features of Myasthenia gravis

A

There are none

38
Q

How is Myasthenia gravis diagnosed?

A

Using electron microscopy

39
Q

Nutritional myopathy is termed?

A

White muscle disease

40
Q

What is the cause of a nutritional myopathy?

A

Selenium and vitamin E deficiency

41
Q

Which spp are affected by nutritional myopathy?

A

Calves, lambs, swine and foals

42
Q

Describe the pathophysiology of nutritional myopathy

A

Lack of anti-oxidant activity of Vit E and Selenium -> membrane damage -> rhabdomyolysis

43
Q

How does a nutritional myopathy appear grossly?

A

Grossly lesions are bilaterally symmetrical. There are multifocal white streaks parallel to the fibre direction with mineralization of cardiac and skeletal muscle

44
Q

How does a nutritional myopathy appear histologically?

A

Multifocal and polyphasic degeneration of the contractile components of the muscle cell

45
Q

Which condition is associated with nutritional myopathy?

A

Adipose tissue necrosis

46
Q

“Equine exertional Rhabdomyolisis” and “Monday Morning Disease” are terms used for which condition?

A

Exertional myopathy

47
Q

What are the causes of exertional myopathy?

A

Inherited basis for the condition being a result of metabolic abnormalities. Associated to exercise without training

48
Q

Describe the pathophysiology of exertional myopathy

A

Aerobic production of ATP not sufficient -> production of ATP by anaerobic glycolysis -> production of lactic acid -> toxic -> membrane damage -> rhabdomyolysis -> myoglobin in blood -> Filtered in kidney -> Myoglobinuria

49
Q

Exertional myopathy occurs mainly in which muscles of the horse?

A

Gluteal
Femoral
Lumbar

50
Q

Describe the histological appearance of exertional myopathy

A

Histologically there is selective necrosis of type II fibres with hypercontraction and hyalinisation

51
Q

What are the two types of bacterial myositis?

A
  • Suppurative Myositis

* Chronic pyogranulomatous fibrosing nodular Myositis

52
Q

What are the causes of suppurative myositis?

A
  • Streptococcus zooepidemicus horses
  • Arcanopbacterium pyogenes, cattle, sheep
  • Corynebacterium pseudotuberculosis horses, sheep, goats
  • Pasturella multocida cats
53
Q

Describe the gross features of suppurative myositis

A

Suppurative lesions, Abscesses

54
Q

What are the two bacterial causes of chronic pyogranulomatous fibrosing nodular myositis?

A
  • Actinobacillus ligneresii (wooden tongue) cattle

- Staphylococcus aureus (botryomycosis) pigs, horses

55
Q

Describe the gross features of chronic pyogranulomatous fibrosing nodular myositis

A

Fibrosing, granulomatous

56
Q

Describe the histological features of chronic pyogranulomatous fibrosing nodular myositis

A

Central focus of radiating clubs of amorphous eosinophilic material associated with bacteria and neutrophils

57
Q

Malignant oedema is caused by which bacterial spp?

A

Clostridium septicum

58
Q

Describe the pathogenesis of malignant oedema

A

Bacteria penetrate in the muscle through a skin wound, then produce toxins that cause the tissue damage

59
Q

Describe the gross appearance of malignant oedema

A

Severe oedema, gas bubbles, cellulitis that dissects the muscle fibres

60
Q

Describe the histological appearance of malignant oedema

A

Muscle fibres are eosinophilic, necrotic.

Not many neutrophils are detected

61
Q

What is the cause of blackleg in sheep and cattle?

A

Clostridium Chauvoei

62
Q

Describe the pathophysiology of blackleg

A

Activation of latent spores in the muscle that colonised the muscle previously. Spores are ingested and subsequently dissemination through blood occurs and colonise the muscle: reactivated by stressors

63
Q

Describe the gross appearance of blackleg

A

Muscles are dark red, oedematous with a dry centre and porous pattern (gas bubbles)

64
Q

Which conditions are associated with blackleg?

A

Liver, kidney degeneration, pleuritis, myocarditis

65
Q

What are the causes of parasitic mysitis in different spp?

A
  • Neospora caninum (dogs)
  • Toxoplasma gondii (dogs, cats)
  • Trichinella spiralis in pigs
  • Sarcocystis spp (horses, cattle, sheep, goats, camelids, pigs)
  • Cysticercus spp (cattle, sheep, dogs, pigs)
66
Q

How does parasitic myositis appear grossly and histologically?

A

G: Grossly visible parasite (Cysticercus) or none
H: Parasite within muscle tissues associated with variable inflammation

67
Q

Eosinophilic Myositis is caused by?

A

Sarcocystis spp - bovine and ovine

68
Q

How does eosinophilic myositis appear grossly

A

Well demarcated, green focal stripes or patches

69
Q

How does eosinophilic myositis appear histologically?

A

Eosinophils, myofibre hypercontraction, necrosis and separation of endomyseal sheaths and perimyseal trabeculae.
There may be fibrosis with lymphocytes, plasma cells and histocytes. Occasional granulomas are present

70
Q

Immunomediated myositis is also termed?

A

“Masticatory muscle myositis”

71
Q

Immunomediated myositis affects which spp?

A

Dogs

72
Q

Describe the pathophysiology of Immunomediated myositis

A

Antibodies against Myosin Type M2 (only present in masticatory muscles: Masseter, Temporal, Pterygoid)

73
Q

Describe the gross and histological appearance of Immunomediated myositis

A

G: Atrophy of masticatory muscles (Masseter, Temporal, Pterygoid)
H: Acute: eosinophilic myositis. Chronic: fibrosis, multifocal lymphocytes

74
Q

What are two neoplasms of muscles?

A

Rhabdomyoma and Rhabdomyosarcoma

75
Q

Where to Rhabdomyoma and Rhabdomyosarcomas most commonly occur?

A

Heart and skeletal muscles

76
Q

How do Rhabdomyoma and Rhabdomyosarcomas appear histologically?

A

Morphological variants – subdivided into round cell, spindle cell and mixed round and spindle cell
Cross striations are indicative of sarcomeric differentiation – strap cells (elongated multinucleate cells) and racket cells (ovoid cells).

Y3 Musculoskeletal pathology (5 decks)

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