Card Set Information
Last lecture on muscles
Conception to 3.5 months, when # of primary myotubules are established
From 3 months to 7.75 months, creating primary and secondary myotubules
Muscle fiber hypertrophy
From 5.5 months on, the increase in muscle mass
Occurs primarily during prenatal (embryonic & fetal)
Somatic growth during prenatal period involved myogenesis (muscle development), adipogenesis and fibrogenesis
(~1st trimester of pregnancy):
Paraxial mesodermal cells differentiate into dermomyotome which gives rise to the early muscle (myotome) and skeletal muscle progenitor cells (mesenchymal stem cells).
Progenitor cells form satellite cells ad embryonic & fetal myoblasts.
: Embryonic myoblasts -> proliferate, elongate, fuse -> myotubes -> 1st wave of primary fibers
(~2 triester of pregnancy)
: Foetal myoblasts -> proliferate, elongate, fuse -> myotubes -> 2nd wave of secondary fibers (majority of skeletal muscle fibers formed)
: of fibers is fixed at end of 2nd trimester of gestation.
Fiber hypertrophy in the last trimester.
Nutrient restriction -> decrease muscle fiber # and muscle mass
: by proliferation & fusion of satelitte cells to muscle fibers
Nutrient restriction -> decrease muscle mass
: myostatin: member of TGFbeta superfamily - expression limited to skeletal muscle-important for inhibiting muscle cell hypertrophy & hyperplasia
Mutations in myostatin - muscle mass increased - "double muscling"
Cattle (belgian blue & Piedmontese:
: denervation -> Lysosomal protein degradation -> decrease 50% muscle mass + EMG abnormalities (Sweeney" in horses)
: Malnutrition, cachexia (weight loss secondary to other diseases), corticosteroid excess
Slow progression, normal EMG, atrophy only to type 2 fibers
Muscle necrosis or Rhabdomyolysis
Tying up/Monday morning sickness/Azoturia. May affect fiber or subgroup of sarcomeres within a fiber - loss of striations
: muscle pain, contracture, increased respiratory rate & sweating: increase Creatine Kinase & aspartate transaminase in serum; myoglobinuria
: Nutrition: deficiency of Vitamin E and Selenium (anti-oxidants) "white muscle disease" - degenerative disease of skeletal and cardiac muscle: hypokalemia; Toxins (ionophores)
Infectious (clostridial, viral, toxoplasmosis, sarcocysts)
Immune mediated (masticatory muscle myositis - dogs)
Metabolic (Glycogenoses, Lipid storage disorders)
Inherited - progressive degeneration of skeletal muscle in small animals
Duchenne's muscular dystrophy- human. Dogs - German short hair pointers, Golden retrieves
: puppies - stunted growth, elbow abduction, bunny hop-like gait; adult- "plantigrade stance"
Deficiency of "dystrophin" - a protein that anchors sarcolemma to actin of cytoskeleton - sarcolemma leakage - fiber damage
Altered electrical conduction
Altered motor neuron firing
Altered motor end plate depolarization
: Myasthenia gravis, congenital deficiency of Ach receptors#, acquired - autoantibodies to Ach receptor and Botulism: clostridium botulinum toxin
Altered sarcolemma excitability
: myotonia - muscle hypertrophy, stiffness, rigidity, prolonged muscle contraction and Goats: autosomal dominant mutation in Cl- channel