Peripheral Nerve & Skeletal Muscle Part 1 Flashcards
What is segmental demyelination?
What is a denuded axon?
What is a characteristic of the new myelination?
Primary involvement of Schwann cell & loss of myelin; no primary abn in axon
- Does not affect all Schwann cells (segmental)
Denuded axon is the stimulus for remyelination
Newly myelinated internodes are shorter than normal; concentric layers of Schwann cytoplasm and redundant BM surrounding thinly myelinated axon (onion bulbs)
What is denervation atrophy?
What is myopathy?
Follows loss of axon
Primary abnormality of muscle fiber itself
What is axonal degeneration?
What is denervation atrophy?
What are myelin ovoids?
Primary involvement of neuron & its axon; may be followed by axonal regeneration & reinnervation of muscle
- W axonal degeneration as muscle fibers in motor units lose input they will undergo denervation atrophy; atrophic fibers will become small and triangular
Schwann cells catabolize myelin & later engulf axon fragments producing small oval compartments
What is a traumatic neuroma?
Pseudotumor; outgrowing neurons can’t find their distal target so they become a haphazard whorled proliferation of axonal processes– painful
What is important to note about nerve regeneration and reinnervation of muscle?
Reinnervation of skeletal muscle changes its composition and the fiber type is determined by the neuron of the motor unit
- Normally there is a checkboard appearance as multiple neurons innervate a motor unit but as a neuron dies the living ones will innervate more of the fibers
What is type 2 fiber atrophy? (2)
- Inactivity or disuse causes atrophy
- Glucocorticoid therapy causes atrophy
Common in ICU settings– both disuse and steroids
What is segmental necrosis in a muscle fiber?
What does this signify as a disease process?
Destruction of a portion of myocyte followed by myophagocytosis (macrophages); loss of muscle fiber leads to deposition of collagen and fat
- This is an end-stage for everyone w muscle fiber loss, not unique to a certain type
What are the 4 pathological reactions of muscle fiber?
- Segmental necrosis
- Vacuolization, alterations in structural proteins or organelles, accumulation of intracytoplasmic deposits
- Regeneration
- Hypertrophy (muscle fiber splitting)
What do we see in regeneration of muscle fibers?
Regenerating portion has large internalizaed central nuclei; cytoplasm laden w RNA is red (trichrome stain)
- “Ragged red fiber”
What do we see with muscle fiber hypertrophy?
Response to an inc load either through exercise or pathologic condition
- Muscle fiber splitting: Large fibers may divide longitudinally; cross section = single large fiber w a cell membrane traversing its diameter often w adjacent nuclei
What do we see in axonal neuropathies?
Which axons are most susceptible?
What is the electrophysiological hallmark of axonal neuropathies?
Axons are the primary target ; growth cone regeneration begins at site of transection
- Degeneration & regeneration axons coexist in sinlge bx; w time, damage tends to outpace repair
Longest axons are most susceptible resulting in a “dying-back” type pattern of progression
EP hallmark: Reduction in single amplitude w relative preservation of conduction velocity
What do we see in demyelinating neuropathies?
What is the electrophysiological hallmark?
Schwann cells w their myelin sheaths are primary targets of damage, axons relatively spared
- New myelin sheaths are shorter and thinner
EP hallmark: Slowed nerve conduction velocity (myelin loss)
What do we see in neuronopathies? What can cause them?
What part of the body is affected?
Destruction of neurons w secondary degeneration of axonal processes
- Can be d/t infections or toxins
- Affect proximal and distal parts of body (whereas periph axonopathies affect only distal)
What is pain characteristic in peripheral neuropathy?
Tingling, stabbing, burning, “pins and needles”
Some characteristics of polyneuropathies?
Multiple nerves, usually symmetric
- Start at the feet and ascend
- Hand deficits same time as knee w “stocking & glove distribution”
