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