Skeletal muscle Flashcards
Cause of denervation atrophy
caused by lost connection to peripheral nerves
- unaffected motor neuron has compensatory hypertrophy
Type 1 muscle fiber v. type 2
type 1- slow (marathon runner)
Type 2- fast twitch (sprinter)
Cause of disuse atrophy
decreased contractile activity of innervated muscles causing a uniform atrophy (ex. painful lameness, fx, bone disease)
Cause atrophy from malnutrition/cachexia
caused by inability to support dietary nutrition to maintain muscle mass~ causes generalized atrophy
- cachexia is associated with neoplasia & chronic illness
Cause atrophy of endocrine disease
associated with hypothyroidism & hyperglucocorticoidism
i. Primarily selective type 2 atrophy with no compensatory type 1 hypertrophy
myopathic atrophy
muscle atrophy after primary muscle disease (ex. inflammatory muscle disease)
4 different patterns of myofiber necrosis
Focal monophasic rxn- infarct
Multifocal monophasic rxn- toxin
Focal polyphasic rxn- repeat injury/same site
Multifocal polyphasic rxn- nutritional myopathies
What gene is responsible for “double muscling”
defective myostatin gene affecting cattle, dogs & sheep
What is muscular dystrophy?
X-linked recessive disorder caused by defects in the gene encoding dystrophin.
hyperkalemic periodic paralysis (HYPP) disease mechanism
ion channel defect affecting sodium channel (muscle) that alters muscle membrane potential.
HYPP clinical signs
muscle fasciculations (spams), 3rd eyelid flashing, collapse
Best way to confirm HYPP
DNA testing
What breeds are predisposed to polysaccharide storage myopathy
draft horses, warmbloods & quarter horses
CS of PSM
recurrent exertional rhabdomyolysis–> progressive weakness
What gene is associated with the PSM?
mutated GYS1
Mechanism of congenital myasthenia gravis
inherited defect in acetylcholine end plate receptor (autosomal recessive in dogs)
Mechanism of acquired myasthenia gravis
circulating antibodies to motor end plate acetylcholine receptors bind & form immune complexes at NM junction
What is the diagnostic method for myasthenia gravis?
Electrodiagnostic testing, positive response to anti-cholinesterase therapy & detection of circulating anti-acetylcholine receptor antibodies.
Malignant hyperthermia mechanism
defective ryanodine receptor causes a calcium release from sarcoplasmic reticulum.
MH pathogenesis
prolonged myofiber contraction & muscle rigidity –> tachycardia, metabolic acidosis & hyperthermia (life threatening)
domestic animal species affected by malignant hyperthermia
humans, pigs, horses & dogs
Splayleg (condition with corresponding lesion)
congenital muscle condition of piglets and corresponding histopathologic lesion is myofibrillar hypoplasia.
Compartment pathogenesis
increase muscle contraction causes increased muscle diameter & pressure
- -> venous outflow collapse, continuous arterial blood supply that causes muscle metabolite accumulation and increases interstitial water
- -> exacerbates intramuscular pressure & blood flow stops causing ischemic necrosis of muscle (worsens in 1-4 hr.)
Compartment disease example
pectoral muscles in turkeys and chickens
Nutritional myopathy- gross changes
muscle pallor, pale streaking affecting weight bearing muscles (though, shoulder, intercostal muscles, diaphragm & tongue)
What type of histologic change occurs with nutritional myopathy?
polyphasic myofiber necrosis
What is an underlying cause of equine exertional rhabdomyolysis?
equine polysaccharide storage myopathy
What are potential effects of widespread rhabdomyolysis on the kidney?
myoglobininuric nephrosis & renal failure
Ionophore effect on muscle
acute monophasic myofiber necrosis (affect skeletal & cardiac m.), once cardiac muscle is damaged it is replaced with fibrosis
Senna spp. effect on muscle
acute monophasic myofiber necrosis (skeletal muscle)
Gossypol effect on muscle
acute segmental myofiber necrosis ( skeletal & myocardium) + hepatotoxic
What are different types of immune-meditated myositis in dogs?
Masticatory myositis
Polymyositis
Bilateral extra-ocular muscle myositis
How do you diagnose immune mediated myositis in dogs?
distribution of affected muscles
histopathology
detection of serum type 2M antibodies (masticatory myositis)
What are different bacterial agents of clostridial myositis?
a. Blackleg: C. chauvoei
b. Malignant edema: C. speticum
c. Gas gangrene: C. perfringes
d. Swelled head (sheep): C. novyi
Gross changes observed with black leg?
i. Muscle is dark red/black, emphysematous & smell like rancid butter
ii. Fibrinous/ fibrohemorrhagic pleuritis & pericarditis
What is the best diagnostic method for detecting black leg?
fluorescent antibody testing (hard to culture)
What is a benign tumor of striated myofiber?
rhabdomyoma
What is malignant neoplasm of myofiber?
Rhabdomyosarcoma
List 5 primary muscle tumors of non- muscle origin
soft tissue sarcomas, HAS, LSA, granular cell tumor & infiltrative lipoma
