General Reactions of Motor Units

Question 1

What are the 4 general reactions of the motor units?

Answer 1

1. Segmental Demyelination
2. Axonal Degeneration and Muscle Fiber Atrophy
3. Nerve Regeneration and Re-innervation of muscle
4. Reactions of the Muscle Fiber

Question 2

What are the 4 general reactions of the motor units?

Answer 2

1. Segmental Demyelination
2. Axonal Degeneration and Muscle fiber atrophy
3. Nerve Regeneration and Re-innervation of muscle
4. Reactions of Muscle fibers

Question 3

With Neuromuscular diseases, what is the main symptom due to disorder of the motor unit?

Answer 3

Weakness

Question 4

There are 2 possible responses of peripheral nerves to injury. What are they?

Answer 4

1. Segmental Demyelination

2. Axonal Degeneration

Question 5

There are 2 pathologic processes seen in the muscle. What are they?

Answer 5

1. Denervation atrophy following loss of axon

2. Myopathy

Question 6

With Segmental Demyelination, where is the dysfunction or damage?

Answer 6

Dysfunction of Schwann cell

Damage to myelin sheath

Question 7

What histologic change is seen with Segmental Demyelination?

Answer 7

Onion bulbs

= Concentric layers of Schwann cytoplasm and basement membrane surrounding thinly myelinated axon

Question 8

When do you seen Onion Bulbs?

Answer 8

Segmental Demyelination

= concentric layers of Schwann cytoplasm and basement membranes surrounding thinly myelinated axon

Question 9

With Axonal Degeneration, there is axon destruction. What does that cause to disintegrate?

Answer 9

Myelin sheath disintegrates

Question 10

If there is a focal lesion on the axon, what does the distal portion undergo?

Answer 10

Wallerian Degeneration

Question 11

What histologic change is seen with Axonal Degeneration?

Answer 11

Myelin Ovoids

= Schwann cells catabolize myelin and engulf axon fragments which produces small oval compartments

Question 12

When do you seen Myelin Ovoids?

Answer 12

Axonal Degeneration

= Schwann cell catabolize myelin and engulf axon fragments which produces small oval compartments

Question 13

With Axonal Degeneration, what does that cause to happen to the muscle?

Answer 13

Denervation muscle atrophy

Question 14

When muscles undergo denervation atrophy following the loss of an axon, what are the 2 things that may be seen?

Answer 14

1. Angulated fibers

2. Target fibers

Question 15

What are the things that may be seen in the muscle following denervation atrophy and what do they look like?

Answer 15

1. Angulated fibers = small triangle myocytes

2. Target fibers = disorganized rounded zone in center of myocyte

Question 16

Nerve are capable of regeneration and re-innervating muscle. What cells provide the guide for growth?

Answer 16

Empty Schwann cells

Question 17

What determines the muscle fiber type?

Answer 17

Motor neuron

Question 18

ALL muscle fibers of a ____ are of the same type

Answer 18

Single unit = same type

Question 19

What is type grouping of a muscle and when is it seen?

Answer 19

Patch of myocytes have same histochemical type

– Seen with nerve regeneration and muscle re-innervation

Question 20

Specifically, when will you see Type 2 muscle fiber atrophy?

Answer 20

Inactivity
Neurodegenerative disease
Glucocorticoid therapy

Question 21

Normally, how do myocytes look?

Answer 21

Checkerboard pattern

Question 22

If muscle fibers undergo segmental necrosis, what will replace the muscle fiber?

Answer 22

Collagen and fat

Question 23

If muscle fibers hypertrophy, what will be seen histologically?

Answer 23

Muscle fiber splitting

= Large fiber with cell membrane traversing diameter

Question 24

When will you see muscle fiber splitting?

Answer 24

Muscle fiber hypertrophy

– large fiber with cell membrane traversing diameter

Question 25

If a muscle fiber regenerates, what color will the cytoplasm be?

Answer 25

Red due to the abundant RNA

Question 26

If a peripheral nerve undergoes Axonal Neuropathy, what will that cause to occur?

Answer 26

DECREASED signal amplitude

– normal conduction velocity

Question 27

If a peripheral nerve undergoes Demyelinating Neuropathy, what will that cause to occur?

Answer 27

DECREASED conduction velocity

Question 28

If a peripheral nerve undergoes neuronopathy, what body parts will be affected?

Answer 28

Proximal and distal body parts affected

Question 29

What are 3 possible anatomic patterns of peripheral neuropathies?

Answer 29

1. Mononeuropathy
2. Polyneuropathy
3. Mononeuritis Multiplex

Question 30

What are the signs that the anatomic pattern of a peripheral neuropathy is a polyneuropathy?

Answer 30

Deficits start at feet and ascend

– “stocking and glove pattern” = up to knee and hand at the same time

Question 31

What is the Mononeuritis Multiplex anatomic pattern of peripheral neuropathy?

Answer 31

Several nerves are damaged in haphazard fashion

Question 32

Several nerves are damaged in a haphazard fashion with a peripheral neuropathy

Answer 32

Mononeuritis Multiplex

Question 33

What is a common cause of a Mononeuritis Multiplex pattern of peripheral neuropathy?

Answer 33

Vasculitis

Question 34

What are 3 common symptoms of Neuromuscular Diseases?

Answer 34

Weakness
Muscle pain
Sensory Deficits

Question 35

What are 3 common symptoms of Neuromuscular Diseases?

Answer 35

Weakness
Muscle pain
Sensory deficits