General Reactions of Motor Units Flashcards
What are the 4 general reactions of the motor units?
- Segmental Demyelination
- Axonal Degeneration and Muscle Fiber Atrophy
- Nerve Regeneration and Re-innervation of muscle
- Reactions of the Muscle Fiber
What are the 4 general reactions of the motor units?
- Segmental Demyelination
- Axonal Degeneration and Muscle fiber atrophy
- Nerve Regeneration and Re-innervation of muscle
- Reactions of Muscle fibers
With Neuromuscular diseases, what is the main symptom due to disorder of the motor unit?
Weakness
There are 2 possible responses of peripheral nerves to injury. What are they?
- Segmental Demyelination
2. Axonal Degeneration
There are 2 pathologic processes seen in the muscle. What are they?
- Denervation atrophy following loss of axon
2. Myopathy
With Segmental Demyelination, where is the dysfunction or damage?
Dysfunction of Schwann cell
Damage to myelin sheath
What histologic change is seen with Segmental Demyelination?
Onion bulbs
= Concentric layers of Schwann cytoplasm and basement membrane surrounding thinly myelinated axon
When do you seen Onion Bulbs?
Segmental Demyelination
= concentric layers of Schwann cytoplasm and basement membranes surrounding thinly myelinated axon
With Axonal Degeneration, there is axon destruction. What does that cause to disintegrate?
Myelin sheath disintegrates
If there is a focal lesion on the axon, what does the distal portion undergo?
Wallerian Degeneration
What histologic change is seen with Axonal Degeneration?
Myelin Ovoids
= Schwann cells catabolize myelin and engulf axon fragments which produces small oval compartments
When do you seen Myelin Ovoids?
Axonal Degeneration
= Schwann cell catabolize myelin and engulf axon fragments which produces small oval compartments
With Axonal Degeneration, what does that cause to happen to the muscle?
Denervation muscle atrophy
When muscles undergo denervation atrophy following the loss of an axon, what are the 2 things that may be seen?
- Angulated fibers
2. Target fibers
What are the things that may be seen in the muscle following denervation atrophy and what do they look like?
- Angulated fibers = small triangle myocytes
2. Target fibers = disorganized rounded zone in center of myocyte
Nerve are capable of regeneration and re-innervating muscle. What cells provide the guide for growth?
Empty Schwann cells
What determines the muscle fiber type?
Motor neuron
ALL muscle fibers of a ____ are of the same type
Single unit = same type
What is type grouping of a muscle and when is it seen?
Patch of myocytes have same histochemical type
– Seen with nerve regeneration and muscle re-innervation
Specifically, when will you see Type 2 muscle fiber atrophy?
Inactivity
Neurodegenerative disease
Glucocorticoid therapy
Normally, how do myocytes look?
Checkerboard pattern
If muscle fibers undergo segmental necrosis, what will replace the muscle fiber?
Collagen and fat
If muscle fibers hypertrophy, what will be seen histologically?
Muscle fiber splitting
= Large fiber with cell membrane traversing diameter
When will you see muscle fiber splitting?
Muscle fiber hypertrophy
– large fiber with cell membrane traversing diameter
