SDL: Diseases of Skeletal Muscle and Peripheral Nerves Flashcards
type I muscle fiber characteristics
red, slow myosin, endurance, rich in mitochondria
type II muscle fiber characteristics
white, fast myosin, strength and speed, rich in glycolytic enzymes and glycogen
the delicate, barely visible connective tissue amongst the myofibers
endomysium
“checkboard” distribution of white fibers vs dark fibers depends on..
the pH of the ATPase reaction, so its variable.
board categories of muscle diseases and their differences
neurogenic (stems from nerve) atrophy, myopathic (steoms from muscle itself) atrophy
progression of chronic denervation
normal muscle, motor unit loss with small group atrophy, collateral axonal sprouting, reinnervation, fiber type grouping with giant motor units, further motor unit loss with large group atrophy
fiber type is decided by..
the neuron type innervating that particular myofiber
denervated fibers have an _______ appearance
angulated atrophic
what is fiber type grouping?
when the denervated orphan fiber is taken over by the other type of nerve fibers, they all become the same type.
if its a nerve injury, the muscle remains at this stage from then on
collateral axonal sprouting, reinnervation, fiber type grouping
if denervation is being caused by a disease, at some point..
the neuron innervating the large group of 1 type of fibers will also degenerate, leaving the entire group atrophic
in early denervation, loss of motor units leads to
small angular fibers, involvement of both fiber types
in chronic denervation, axonal sprouting and reinnervation leads to
large motor units, fiber type grouping
in late denervation, loss of large motor units leads to
grouped atrophy
in fiber type grouping, do you see checkerboard appearance?
no, because they are the same fiber type
neurodegenerative disorder where neurons in the spinal cord are constantly degenerating
spinal muscular atrophies (motor neuron disease)
disease of the neuromuscular junction where autoantibodies produced against ACh receptors on the post-synaptic membrane
myasthenia gravis
pathology of myasthenic neuromuscular junction
simplified post synaptic folds to increase SA, compensatory proliferation of presynaptic vesicles;
what does c. botulinum toxin block?
ACh release by interfering with the fusion proteins involved in membrane fusion between axon membrane and the synaptic vesicle membrane
general myopathic changes
myofiber degeneration or regeneration, internalization of nuclei, increased endomysial connective tissue (scar), inflammation, vacuolation
inherited myopathies examples
Duchenne’s and Becker (x-linked and autosomal)
metabolic myopathies examples
lipid and glycogen storage diseases
what causes ragged red fiber on muscle slides?
compensatory proliferation of mitochondria in mitochondrial disorders
type II atrophy of muscle is seen with..
disuse, chronic disease, cachexia, corticosteroids
*most important primary inflammatory myopathies
polymyositis, dermatomyositis, inclusion body myositis
what is polymyositis?
autoimmune disorder involving infiltrates containing CD8 cytotoxic T cells; leads to myofiber necrosis
what is dermatomyositis?
most common inflammatory myopathy in kids; autoimmune basis; can be paraneoplastic in adults
what is inclusion body myositis?
most common inflammatory myopathy in patients 60 years and older; inflammation is probs a secondary event; could be a degenerative disease of aging specifically
what is the pathology of polymyositis?
intrafascicular inflammation
what is the pathogenesis of polymyositis? whats the clinical presentation?
cytotoxic T cell; pain
what is the pathology of dermatomyositis?
extrafascicular inflammation; perifascicular atrophy
what is the pathogenesis of dermatomyositis? what is the clinical presentation?
humoral; pain and rash
what is the pathology of inclusion body myositis?
inclusions; rimmed vacuoles
what is the pathogenesis of inclusion body myositis? the clinical presentation?
degenerative; steroid resistance
where is the inflammation in dermatomyositis located?
in the perimysium, the connective tissue around the fascicle (the endomysium is within the fascicle)
inclusion body myositis is represented by..
rimmed vacuole
the muscular dystrophies
Duchenne MD, Becker MD, myotonic dystrophy
Duchenne MD path characteristics
endoysial fibrosis with fiber (rounding), variation in fiber size, myofiber regeneration (small blue fibers)
congenital myopathies (what are they named after?)
central core, rod body, centronuclear (they’re microscopic appearance)
