MSK 4

Question 1

What are the three main types of muscle?

Answer 1

1. Skeletal (striated, voluntary, ex. muscles attached to skeleton)
2. Cardiac (striated, involuntary, ex. myocardium)
3. Smooth (Not striated, involuntary, ex. blood vessels and GI viscera)

Question 2

What is a myofiber?

Answer 2

A tubular muscle cell (also called a muscle fiber)

Question 3

What is the plasma membrane of a muscle cell called?

Answer 3

Sarcolemma

Question 4

What is the cytoplasm of a muscle cell called?

Answer 4

Sarcoplasm

Question 5

Describe the nucleus of skeletal muscle fibers.

Answer 5

They are multinucleated and located in the periphery of the cell.

Question 6

True or False: Skeletal muscle cells have terminal differentiation.

Answer 6

True. Skeletal muscle cells cannot divide to replace injured/damaged cells because they are not mitotically active.

Question 7

What are satellite cells?

Answer 7

Mitotically active skeletal muscle precursor cells (called myoblasts).

Question 8

True or False: Satellite cells have terminal differentiation.

Answer 8

False. They are capable of dividing and reforming myofibers (muscle regeneration).

Question 9

What are muscle types determined by?

Answer 9

The activity of the innervating motor neuron.

Question 10

What is a motor unit?

Answer 10

A muscle fiber(s) + an innervating motor neuron.

Question 11

True or False: In a motor unit, there is simultaneous contraction of all muscle fibers.

Answer 11

True. All muscle cells innervated by the same motor neuron will contract at the same time.

Question 12

What does pale muscle look like grossly?

Answer 12

It is pink or white and usually indicates necrosis with or without mineralization.

Question 13

What is muscle atrophy?

Answer 13

A reversible reduction in muscle volume or mass.

Question 14

What do you see microscopically with muscle atrophy?

Answer 14

Decreased size (diameter) of muscle fibers rather than loss of muscle fibers.

Question 15

What are the four common causes of muscle atrophy?

Answer 15

1. Denervation
2. Disuse
3. Malnutrition/cachexia
4. Endocrine

Question 16

Describe denervation atrophy.

Answer 16

• Characterized by rapid atrophy (muscle is half the size in a matter of weeks)
• Long‐standing denervation may result in fibrosis & fat infiltration (steatosis) of affected muscles.
• Type 1 & 2 myofibers affected
• Also called neurogenic atrophy.

Question 17

Describe disuse atrophy.

Answer 17

• The innervation of the muscle is intact
• Atrophy is due to immobilization of a limb or body part because of pain (fracture, tenotomy, ankylosis)
• May also be caused by a primary muscle disease (myopathy)
• Primarily affects type 2 myofibers.

Question 18

Describe malnutrition or cachexia muscle atrophy.

Answer 18

• Physical wasting due to malnutrition or associated with chronic disease or neoplasia
• May have a normal appetite and nutrient intake (cachexia)
• Occurs slowly over time
• Type 2 myofibers primarily affected.

Question 19

Describe endocrine muscle atrophy.

Answer 19

• Examples include hypothyroidism and hyperadrenocorticism (Cushing’s disease).
• Primarily affects type 2 myofibers.

Question 20

What is muscle hypertrophy?

Answer 20

Reversible increase in muscle volume or mass due to an increase in the size (diameter) of muscle fibers, but the number of muscle fibers (cells) do not increase.

Question 21

What is muscle hyperplasia?

Answer 21

An increase in muscle volume or mass due to an increase in the number of muscle fibers with no change in size or structure.

Question 22

What is muscle necrosis? What is another name for it?

Answer 22

A common sequela of muscle fiber injury regardless of its cause.

Also called myonecrosis.

Question 23

What are the two types of muscle necrosis?

Answer 23

1. Segmental (Zenker’s degeneration): Death of a portion of a muscle fiber.
2. Global: Death of entire muscle fiber.

Question 24

What is a common histologic feature of muscle fiber necrosis?

Answer 24

Mineralization. Calcium is released when muscle cell dies, leading to mineralization.

Question 25

What does the ability for muscle to regenerate depend on?

Answer 25

1. Preservation of satellite cells 2. Preservation of basal lamina 3. An adequate blood supply 4. Removal of necrotic debris.

Question 26

If one or more of the muscle regeneration factors is missing, what replaces the necrotic muscle?

Answer 26

Fibrous tissue (scar).

Question 27

What would you see on histology with a monophasic muscle injury?

Answer 27

The histologic changes are all of the same duration (suggests a single insult).

Question 28

What would you see on histology with a polyphasic muscle injury?

Answer 28

The histologic changes are of variable duration (suggests ongoing muscle damage).

Question 29

What are the four categories of muscle injury?

Answer 29

1. Focal monophasic muscle injury 2. Multifocal monophasic muscle injury 3. Focal polyphasic muscle injury 4. Multifocal polyphasic muscle injury.

Question 30

What is congenital muscular hyperplasia? What is a common term for this?

Answer 30

When there is an increase in the number of muscle fibers (true hyperplasia), but the muscle fibers are of normal size. ## Footnote Also called 'double muscling' of cattle.

Question 31

What is congenital muscular hyperplasia caused by?

Answer 31

A defect in the myostatin gene (this gene normally limits growth).

Question 32

What is muscular dystrophy characterized by?

Answer 32

Ongoing myofiber necrosis and regeneration.

Question 33

What is muscular dystrophy?

Answer 33

An inherited and progressive degenerative disease.

Question 34

What classification of lesion does muscular dystrophy cause?

Answer 34

It causes multifocal polyphasic lesions.

Question 35

What is muscular dystrophy caused by?

Answer 35

A defect in the dystrophin gene.

Question 36

What is myotonia?

Answer 36

A temporary inability of skeletal muscle fibers to relax (muscle stiffness/prolonged muscle contraction). ## Footnote Ex. Fainting goats.

Question 37

What is myotonia caused by?

Answer 37

Electrical abnormalities of the sarcolemma due to inherited defects in the membrane ion channels.

Question 38

What is hyperkalemic periodic paralysis (HYPP)?

Answer 38

A hereditary myopathy in horses that causes transient attacks of paralysis.

Question 39

What is the difference between HYPP and myotonia?

Answer 39

HYPP is associated with hypotonia rather than hypertonicity.

Question 40

What is hyperkalemic periodic paralysis (HYPP) caused by?

Answer 40

A mutation in muscle sodium channels.

Question 41

What are metabolic myopathies characterized by?

Answer 41

Accumulation of intracytoplasmic glycogen in muscle fibers.

Question 42

What is Equine Polysaccharide Storage Myopathy (EPSM)?

Answer 42

A metabolic myopathy in horses caused by accumulation of glycogen in muscle fibers.

Question 43

What animals are affected by malignant hyperthermia?

Answer 43

Pigs, horses, and some dogs.

Question 44

What is malignant hyperthermia caused by?

Answer 44

A defect in the ryanodine receptor gene.

Question 45

What is the pathogenesis of malignant hyperthermia?

Answer 45

Stress or anesthesia → sudden increase in intracytoplasmic calcium → prolonged muscle fiber contraction.

Question 46

What is malignant hyperthermia also called?

Answer 46

'Pale, soft, exudative pork.'

Question 47

What is nutritional myopathy? What is it commonly referred to as?

Answer 47

A deficiency of selenium and Vitamin E. ## Footnote It is called white muscle disease.

Question 48

What are ionophores?

Answer 48

Growth promoting feed additives for cattle and poultry.

Question 49

What gross lesions do you see with ionophore toxicity?

Answer 49

Necrosis of cardiac muscle +/‐ skeletal muscle +/‐ myoglobinuria.

Question 50

What is the muscle fiber damage in exertional myopathies caused by?

Answer 50

Exercise stress.

Question 51

Exertional myopathies are associated with which two main clinical signs?

Answer 51

1. Rhabdomyolysis 2. Myoglobinuria.

Question 52

What is capture myopathy?

Answer 52

A form of exertional myopathy that occurs in many species of wildlife.

Question 53

What is circulatory myopathy?

Answer 53

When blood flow to a muscle is blocked.

Question 54

What is compartment syndrome?

Answer 54

An example of a circulatory myopathy caused by increased intramuscular pressure.

Question 55

What is downer syndrome?

Answer 55

An example of a circulatory myopathy caused by a heavy large animal sitting on their side.

Question 56

What are clostridia?

Answer 56

Gram‐positive, anaerobic, and spore‐forming bacteria that exist within the environment.

Question 57

What do clostridial bacteria produce?

Answer 57

Potent exotoxins.

Question 58

What is blackleg caused by? What animal does it commonly occur in?

Answer 58

It is caused by Clostridium chauvoei and most commonly occurs in cattle.

Question 59

What age of animal does blackleg affect?

Answer 59

9 months - 2 years old.

Question 60

What does muscle look like that's infected with blackleg (grossly)?

Answer 60

Muscles are dark red to black and dull with gas bubbles, abundant yellow gelatinous edema.

Question 61

What are three types of parasitic myositis?

Answer 61

1. Trichinellosis 2. Cysticercosis 3. Sarcocystosis.

Question 62

True or False: Sarcocysts are a very common incidental finding in skeletal muscle of domestic herbivores.

Answer 62

True.

Question 63

What is polymyositis of dogs?

Answer 63

A generalized immune‐mediated myositis.

Question 64

What is masticatory muscle myositis?

Answer 64

An immune‐mediated myositis of the masticatory muscles.

Question 65

What is the primary differential diagnosis for masticatory myositis?

Answer 65

Polymyositis.

Question 66

What is masticatory muscle myositis caused by?

Answer 66

Auto‐antibodies directed against type 2M myosin.

Question 67

How can you tell the difference between masticatory muscle myositis and polymyositis?

Answer 67

With masticatory myositis you see 2M myosin antibodies, but in polymyositis you don't.

Question 68

Is rhabdomyoma benign or malignant?

Answer 68

Benign.

Question 69

Is rhabdomyosarcoma benign or malignant?

Answer 69

Malignant.

Question 70

What is rhabdomyosarcoma?

Answer 70

A malignant, locally invasive neoplasm that frequently metastasizes.

Question 71

What location does rhabdomyosarcoma particularly like?

Answer 71

The bladder.

Question 72

What are the two striated muscle neoplasms?

Answer 72

Rhabdomyoma and rhabdomyosarcoma.