Muscle Pathology Flashcards
what are the types of muscle fibres
type 1 and type 2
how many mitochondria do type 1 and type 2 have
1: many
2: fewer
what is the metabolism of type 1 and 2 muscle fibres
1: oxidative (aerobic)
2. glycolytic (anaerobic)
what type of contraction do type 1 and 2 muscle fibres have
1: slow
2: fast
which muscle fibres fatigue more easily
1: slow
2: more easily
which type of muscle is 1 and 2 fibres
1: postural
2: propulsive
what colour are type 1 and 2 muscle fibres
1: red
2: white
what are the fibres like in type 1 and 2
1: smallest
2: 2B is largest (fast-contracting, fast-fatiguable, glycolytic) 2A: mixed oxidative-glycolytic; fast-contracting, slow-fatigueing (intermediate)
what is the mixed mosiac pattern
most muscles contain both type 1 and 2 fibres
proportion varies dependent on muscle function
determined by motor neuron
which muscle fibre do dogs not have
type 2B
what is rigor mortis
sustained muscle contraction after death
what causes rigor mortis
absence of adequate ATP production –> actin and myosin cannot be released from eachother
how is rigor mortis stopped
muscle breakdown (autolysis)
variable onset and resolution depending on intrinsic and extrinsic factors (temp, etc)
what is a motor unit
myofibres innervated by a single axon
how are fine movements produced
small motor units –> 1-4 myofibres per axon
how are large forces generated
large motor units –> 100-150 myofibres per axon
how are muscles examined using clinical pathology
CK, ALT (AST, LDH less specific)
myoglobin
integrity not function
how can muscles be examined using electrophysiology
electromyography
electroneurography
what are gross examination features of muscle ex vivo
- size
- colour
- texture
- histological examination
what changes colour changes of muscles indicate
- pale pink/white: anemia, young animal, ischemic necrosis, mineralization, collagen, fat
- red: congestion, hemorrhage, hemorrhagic, necrosis, inflammation, myoglobin staining
- green: eosinophils, severe putrefaction
- tan-brown: lipofuscin
- black: melanosis in calves
what texture changes occur in muscles
soft: fat, necrosis
firm: fibrosis
hard: mineralization
what needs to be considered when muscles are biopsied
certain muscles easier to sample due to longitudinal orientation
- type of muscle: proximal/distal
- certain muscle/muscle groups: ex. masticatory muscle myositis
- type of myofibre
- fresh vs. fixed muscle
what are response to insult
- hypertrophy (addition of myofilaments)
- atrophy
- degeneration and necrosis
- regeneration
- chronic myopathic change: alterations in myofibre diameter, fibrosis, fat infiltration, aetiology: chronic inflammation, deneration, degenerative myopathy
often cause for changes not clear on histology –> history and ancillary tests required
what is atrophy
usually reversible
reduced myofibre diameter
what is hyaline degeneration
homogenously eosinophilic fibres, loss of striations
what does regeneration of muscle depend on
muscle is post mitotic tissue
regeneration depends on intact satellite cells and extent of damage to basal lamina
what are the steps of regeneration in muscle
basal lamina intact
- macrophages entre and remove debris
- satellite cells become myoblasts
- myoblasts fuse to form myotubes
- essential structures reformed
- nuclei move to peripheral position
what occurs when the basal lamina is destroyed
if satellite cells survive mutlinucleate muscle giant cells develop
what are the types of muscle pathology
- vascular
- inflammatory (infectious/immune-mediated)
- traumatic
- anomaly/congenital
- metabolic/toxic
- idiopathic/iatrogenic
- neoplastic
- degenrative
what occurs during vascular damage
ischemia
- occlusion of large blood vessel
- external pressure on a muscle (downer cow, anaesthesia)
- internal pressure on a muscle (compartment syndrome)
- vasculitis/vasculopathy
how does inflammatory damage occur
- penetrating wounds
- spread from adjacent sites
- hematogenous
what bacteria causes inflammatory damage to muscle
clostridia –> myonecrosis
CI. perfringens, CI. chauvoei, CI. septicum, CI. novyi
how does bacteria cause inflammatory damage
toxins –> damage to myofibrils and vessels leads to necrosis
what is pyogenic bacteria
abscesses
what parasites cause inflammatory damage
protozoa: Neospora caninum
nematode: trichinella spiralis (pigs), larval migrans (dogs)
cestode: larval form
what are the causes of immune-mediated muscle damage
primarily dogs
usually cytotoxic T cells
what is masticatory muscle myositis
antibodies againts type 2M myosin and myositigen
focal myositis of masticatory muscles
what are traumatic injuries
crushing
lacterations
tearing or ruptures
what is the most common muscle to undergo traumatic injury
diaphragm
what do traumatic injuries normally cause
damage to basement membrane –> fibrosis
what is X-linked muscular dystrophy
absence of membrane associated cytoskeletal protein dystrophin
repeated necrosis and regeneration of fibres
progressive weakness and skeletal muscle atrophy beginning within days of birth
what is labrador centronuclear myopathy
mutation in gene encoding cell surface protein
weakness, gait abnormalities, exercise intolerance
what is hyperkalemic periodic paralysis
membrane instability and continuous myofibre activity
muscle spasm followed by paralysis
what is equine polysaccharide storage myopathy
carbohydrate metabolic disorder
recurring exertional rhabdomyolysis, unexpected pelvic limb lameness
what are metabolic injuries to muscle
oxidative injury due to loss of antioxidant defense mechanisms
what are examples of metabolic injuries
selenium deficiency
vit E deficiency
“white muscle disease”
what are examples of toxic damage to muscle
- ionophores (monensin in horses)
- plants
multifocal and monophasic/polyphasic necrosis
what is exertional (iatrogen) damage
capture myopathy in highly strung wild animal
more often: underlying pre-existing conditions (Se deficiency, muscular dystrophy, electrolyte depletion, glycogen storage dx)
what is primary neoplasm damage
rhabdomyoma
rhabdomyosarcoma
what is secondary neoplasm
injection site sarcoma
round cell tumours: lymphoma, mast cell tumour
infiltrative lipoma
carcinoma
