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
all muscle fibers of a single unit …
are of the same type!!
one slow fat red ox
type 1 fiber slow (twitch) fat (lipid -rich) red (appearance) ox (oxidative)
what type of action and strength is type I fiber
sustained force
weight-bearing
what type of action and strength of type II
sudden movements
purposeful movements
ultrastructure of type I
many mitochondria
wide z band
ultrastructure of type II
few mitochondria
narrow z band
type grouping
happens as a result of reinnervation
it is the loss of the “checkerboard” pattern in muscles (usually type 1 to type 2 switching off)
it is the occurrence of a patch of contiguous myocytes havng the same histochemical type
type 2 atrophy ( a type of group atrophy) is common in what?
inactivity or disuse
may occur after a fracture and placement of a cast
may also occur during use of glucocorticoid therapy “steroid myopathy”
acute neuronal injury
acute CNS hypoxia/ischemia
reflect cell death, either necrosis or apoptosis
RED neurons
shrinkage of the cell body, pyknosis of the nucleus, no nucleolus, loss of Nissl
eosinophilia
Subacute and chronic neuronal injury
degeneration
cell loss
trans-synpatic degeneration
axonal reaction
reaction within the cell body that attends regeneration of the axon
increased protein synthesis
rounding and enlargement of the cell body
peripheral displacement of the nucleus
