Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
75 Cards in this Set
- Front
- Back
|
What are the 2 basic muscle fiber types?
|
-Type I muscle fibers
-Type II muscle fibers |
|
|
What are Type I muscle fibers also known as?
|
Red slow twitch fibers
|
|
|
What are Type II muscle fibers also known as?
|
White fast twitch fibers
|
|
|
Which type of fibers are high in mitochondria/enzymes and fat droplets?
|
Type I red slow twitch
|
|
|
Which type of fibes are high in Glycolytic enzymes phosphorylase and ATPase?
|
Type II white fast twitch
|
|
|
What are 2 main classes of pathological alterations in muscles?
|
-Neurogenic muscular atrophy
-Myopathies |
|
|
So the 2 types of diseases of muscles are:
|
-Neurogenic muscular atrophy
-Myopathies |
|
|
What is neurogenic muscular atrophy?
|
Muscle degeneration secondary to degeneration of the peripheral motor neuron or denervation.
|
|
|
What is the main pathological change seen grossly and microscopically in neurogenic muscular atrophy?
|
Atrophy of muscle fibers
|
|
|
How much muscle mass can be lost due to neurogenic muscular atrophy in a period of 3 months?
|
Up to 70-80%
|
|
|
What types of muscle fibers are usually affected by neurogenic muscular atrophy?
|
Both red/white
|
|
|
What does 3 changes does electron microscopy show in neurogenic muscular atrophy?
|
-Loss of myofilaments
-reduction in myofibril size -degeneration of I bands and Z-lines |
|
|
What are the 3 consecutive stages of denervation changes seen in the evolution of neurogenic muscular atrophy?
|
1. Denervation
2. Reinnervation and type grouping 3. Group atrophy |
|
|
What is the pattern of atrophy seen in the first stage of denervation? Why?
|
Scattered - because that's how the muscle fibers innervated by a single motor neuron are distributed.
|
|
|
What morphology do the atrophic muscle fibers exhibit in the denervation stage?
|
-Pyknotic nuclei
-Excessive staining for oxidative enzymes |
|
|
How does reinnervation occur in neurogenic muscular atrophy?
|
Nerve fibers of unaffected motor neurons produce sprouts of axons which reinnervate the denervated atrophic fibers.
|
|
|
What happens to the muscle fiber type when it is reinnervated?
|
It changes to be the same as the original fibers innervated by the motor neuron which sent out axonal sprouts.
|
|
|
What is the resulting grouping of muscle fibers of the same type called?
|
Type grouping
|
|
|
So if you see type grouping, what do you know?
|
There was denervation and reinnervation of the muscle fibers.
|
|
|
What is the third stage of neurogenic muscular atrophy?
|
Group atrophy
|
|
|
What is group atrophy?
|
Atrophy of all the muscle fibers in the extended motor unit due to disease progression.
|
|
|
What is the difference between neurogenic muscular atrophy and that seen in patients with chronic diseases?
|
-Atrophy is only of type II fibers
-They do not have increased oxidative enzyme staining |
|
|
Will type grouping or group atrophy be seen in muscular atrophy in patients with disuse, cachexia, cancer, etc?
|
No
|
|
|
What is the distribution of degenerating fibers seen in primary myopathies?
|
Random
|
|
|
What is the most characteristic change of primary myopathies?
|
Segmental necrosis of muscle fibers.
|
|
|
What is the appearance of necrotic muscle fibers in early stage myopathies?
|
Hyaline
|
|
|
What is the appearance of necrotic muscle fibers in later stage myopathies?
|
Floccular
|
|
|
What happens to the nuclei of muscle fibers in myopathies?
|
-Nuclei increase
-Migrate internally -Act like macrophages to remove necrotic debris |
|
|
What happens to the general appearance of muscle affected in myopathy?
|
It becomes small and round except in the necrotic area.
|
|
|
What happens at the same time as muscle degeneration in primary myopathies?
|
Regenerative activity
-nucleoli enlarge |
|
|
What do the myocytes have capacity to do in regeneration?
|
Transform into myoblasts, multiply, form myotubes and regenerate muscle fibers.
|
|
|
What does the regenerated muscle fiber look like? Why?
|
Very basophilic due to increased protein synthesis by RNA.
|
|
|
When is regeneration of muscle fibers most prominent in myopathies?
|
During acute stages
|
|
|
What is seen in chronic stages of myopathies?
|
Replacement of degenerative muscle by fibroadipose tissue.
|
|
|
What muscles are affected more often in myopathies?
|
Proximal muscles
|
|
|
What are the 4 main groups of myopathies?
|
-Muscular dystrophies
-Inflammatory myopathies -Congenital myopathies -Miscellaneous groups |
|
|
What are muscular dystrophies?
|
A group of myopathies that show degeneration of muscle fibers with eventual replacement by fibroadipose tissue.
|
|
|
What are 3 specific muscular dystrophies?
|
-Duchenne's type
-Autosomal muscular dystrophies -Myotonic dystrophy |
|
|
When is the typical onset of Duchenne's type MD? What muscles are particularly involved?
|
-Early childhood or infancy
-Proximal limb and trunk |
|
|
How does Duchenne's type MD progress?
|
-Steadily
-Patient in wheelchair by age 10 -Death by age 20 |
|
|
What is the genetic inheritance pattern of Duchenne's type MD?
|
-Sex linked
|
|
|
What is the pathologic cause of Duchenne's type MD?
|
Decrease/loss of dystrophin function leading to membrane instability and myocyte death.
|
|
|
What disease is similar to Duchenne's MD but milder and later-onset?
|
Becker's dystrophy
|
|
|
What muscles are particularly involved in Autosomal muscular dystrophies?
|
Proximal limb/trunk muscles
|
|
|
What clinical sign is positive in patient with muscular dystrophy?
|
Gower's sign - difficulty in getting up
|
|
|
What protein gene is defective and on what chromosome in Myotonic dystrophy?
How is it transmitted genetically? |
-Myotonin protein kinase gene
-Ch 19 - triplet repeats of the gene -Autosomal dominant trait |
|
|
What pathologic changes are seen in muscle fiber due to abnormal myotonin protein kinase?
|
-Type I fibers degenerate, fire repeatedly, and are slow to relax.
|
|
|
What are 3 clinical manifestations often seen in myotonic dystrophy?
|
-Frontal balding
-Cataracts -Gonadal atrophy |
|
|
Where are inflammatory cell infiltrates seen in Inflammatory Myopathies?
|
Distributed diffusely in the -perivascular space
-endomysium -perimysium |
|
|
What is the most common inflammatory myopathy?
|
Polymyositis
|
|
|
What is the onset and progression of Congenital myopathies like in general?
|
-Early onset
-Mild weakness -Slowly progressive |
|
|
What are 2 signs of mild weakness in congenital myopathy?
|
Hypotonia (frog baby)
Delayed postural control |
|
|
What are 4 congenital myopathies?
|
1. Nemalin myopathy
2. Centronuclear myopathy 3. Central core disease 4. Mitochondrial myopathy |
|
|
What does Nemalin mean?
|
Rods/threads
|
|
|
What causes muscle degeneration in Nemalin myopathy?
|
degeneration of Z bands
|
|
|
What is the morphologic hallmark of centronuclear myopathy?
|
Nuclei in the center of muscles
|
|
|
What % of normal adult muscles have central nuclei?
|
<5%
|
|
|
What is the morphologic hallmark of centronuclear myopathy?
|
Core substances made from degenerative myofibrils in the center of muscle fibers.
|
|
|
What causes mitochondrial myopathies?
|
Decreased oxidative enzymes in mitochondria
|
|
|
How are mitochondrial DNA defects inherited?
|
From the mother
|
|
|
What is it called when mitochondrial defects affect both muscle and the heart/brain?
|
Mitochondrial encephalomyopathy
|
|
|
What are 2 mitochondrial encephalomyopathies?
|
MERRF and MELAS
|
|
|
What is MERRF?
|
Myoclonic Epilepsy with Ragged Red Fiber syndrome
|
|
|
What is MELAS?
|
Mitochondrial Encephalopathy with Lactic Acidosis and Stroke-like episodes
|
|
|
What is the amplitude of the AP of a motor neuron proportional to?
|
The number of muscle fibers it innervates.
|
|
|
What is the duration of an AP of a motor neuron proportional to?
|
The area of muscle that it innervates.
|
|
|
What AP amplitude and duration will be seen in a neuropathy?
|
High amplitude
Long duration |
|
|
What AP amplitude and duration will be seen in a Myopathy?
|
-Low amplitude
-Short duration |
|
|
What clinical manifestations will be seen in a neuropathy?
|
-Parasthesia
-Loss of sensation |
|
|
What clinical manifestations will be seen in a myopathy?
|
Local pain, heat sensation, swelling, signs of inflammation.
|
|
|
In what types of myopathy will there be more vs less signs of inflammation?
|
-Inflammatory myopathy most
-Dystrophy less -Congenital myopathy least |
|
|
What happens to nerve conduction velocity in
-Neuropathy -Myopathy |
Neuropathy - decreased
Myopathy - normal |
|
|
Which type of neuropathy shows a more pronounced decrease in nerve conduction velocity?
|
Demyelinating > axonal
|
|
|
In which type of neuromuscular disease will muscle enzymes be increased?
|
Myopathy - proportional to the degree of inflammation.
|
|
|
What muscle enzymes will be elevated in inflammatory myopathy?
|
-CPK1
-LDH -Aldolase |
