Ketchum Neuromuscular Degenerative disorders Flashcards
what makes up a motor unit?
lower motor neuron
axon of that neuron
multiple muscle fibers it innervates
epineurium
CT component covering entire nerve
perineurium
multilayered concentric CT sheath that encloses each fasicle
endoneurium
surrounds individual nerves
nerve that exits the spinal canal is…
MIXED with both sensory and motor
segmental demyelination
random internodes of myelin are injured and are remyelinated by multiple schwann cells, while the myocytes remain intact
this is the result of injury to peripheral nerve, specially to the Schwann cells!
looks like an onion bulb on imaging
no damage to the axon
axonal degeneration
the axon and its myelin sheath undergo anterograde degeneration with resulting denervation atrophy of the myocytes within its motor unit
result of primary destruction of the axon, with secondary disintegration of its myelin sheath
usually caused by some sort of injury/trauma to a nerve
myopathy
scattered myocytes of adjacent motor units are small (degenerated or regenerated) whereas the neurons and nerve fibers are normal
two main pathological processes seen in skeletal muscles are…
denervation atrophy (which follows loss of axons)
myopathy (abnormality of muscle fiber itself)
what happens to muscle fibers within an affected motor unit (that is undergoing axonal degeneration?
los their neural input and undergo denervation atrophy
this leads to break down of myosin and actin, with a decrease in cell size and resorption of myofibrils, but cells remain viable
cytoskeletal reorganization of some muscle cells–> leading to rounded zone of disorganized myofibers
how does reinnervation of muscle occur?
the proximal stumps of degenerated axons sprout and elongate, and they may develop new growth cones that use the schwann cells vacated by the degenerated axons to guide them
how can you increase the rate of axonal regrowth?
marrow stromal cell transplants
Type I fibers
high in myoglobin and oxidative enzymes
many mitochondria in keepin their ability to perform tonic contraction
dark staining for ATPase at pH 4.2 but light staining at pH 9.4
type II fibers
rich in glycolytic enzymes and involved in rapid phasic contractions
dark staining on ATPase stain performed at pH 9.4 but light staining at pH 4.2
what determines the fiber type?
motor neuron
