Pathology of Skeletal Muscle - Part 1

Question 1

Define the endomysium, epimysium, and perimysium.

Answer 1

Muscle fibers are surrounded by layers of CT called the endomysium (individual fibers), perimysium (surrounds fascicles, bundles of muscle fibers), epimysium is the outside layer that holds everything together.

Question 2

The sarcomere is the _______/_____
unit of skeletal muscle and is composed of ________ _______ called _______.

Answer 2

structural/ functional, contractile, proteins, myosin.

Question 3

Successful microscopic evaluation of skeletal muscle requires a good biopsy or autopsy sample. For better results the sample should not be _____ than ___ cm in ________.

What is the most common artifact?

How can this artifact be minimized?

Answer 3

more, 1, diameter,

Contraction of the muscle following contact
with the fixative is the most common artifact (formation of contraction bands).

This can be minimized by the use of special clumps or a tongue depressor.

Question 4

Type I muscle fibers are _____ in color, _____ twitch and ____ fatiguing – rich in ________ and obtain energy from the process of _______ ________.
They rely mainly on the _______ metabolism of ____ for their energy supply. Stain strongly with stains for ______ _________ (___) and lightly with the ______ ______ reaction (e.g.: diaphragm).

Answer 4

red, slow, slow, mitochondria, oxidative phosphorylation, oxidative, fats, succinate dehydrogenase (SDH), myosin-ATPase

Question 5

Stain used: Mitochondria NADH reaction (blue stained)

Label the image below.

Answer 5

Dark blue = Type I
Dark green = Type II

Question 6

Myofibrillar adenosine triphosphatase (ATPase) reaction.

Identify the Type I and Type II muscle fibers in this image.

Answer 6

Type I = light
Type II = darker

Question 7

Type II muscle fibers are ______ in color, ____ twitch and obtain their energy from the process of ______. They have fewer _______ and ______ than type I fibres (therefore are mainly used for _____ ____ of athletic activity, e.g.: _______ and _______ m.). Stains darkly with the ______ ______ reaction.

Answer 7

white, fast, glycolysis, mitochondria, myoglobin, short bursts, longissimus, semitendinosus, myosin-ATPase

Question 8

Muscles may be pale during autopsy. This can be indicative of a case of _______, but this can also occur in _______, especially in calves and is therefore normal. This is called ______ and may be secondary to ________.

Very dark discoloration of muscle can be seen in cases where there is _______ of muscle fibers OR animals that are undergoing _____-________ ______ (Hb). This is called __________ or ________.

Answer 8

anemia, neonates, pallor, anemia.

rupture, post-mortem autolysis, rhabdomyolysis, or putrefaction.

Question 9

Rigor Mortis is defined as the _______ of muscles that occurs after death. Results in stiffening of the _______ and ________ of the joints. Generally starts in the ____ and _____ and progress to the _____.

The rapidity of the onset of rigor mortis depends on many factors such as ________ ______, muscle ___, _______ ______ and _______ reserves in muscle at the time of death.

On average it begins in ___-___ hours after death and
reaches a maximum at about ____ hours; then it disappears gradually in the ?.

Answer 9

contraction, muscles, immobilization, jaws, trunk, limbs, environmental temperature, pH, internal temperature, glycogen, 2,4, 24, same order of sequence

Question 10

Answer 10

Rigor mortis

Question 11

List three examples of growth disturbances

Answer 11

Atrophy, Hypertrophy, Hyperplasia

Question 12

List three examples of reaction to injury

Answer 12

Degeneration/Necrosis, Calcification, Regeneration

Question 13

List three examples of congenital inherited defects

Answer 13

Arthrogryposis; Muscle Dystrophy; PSM; PSS

Question 14

List three examples of nutritional myopathy

Answer 14

white muscle disease

Question 15

List three examples of Exertional myopathies

Answer 15

Azoturia; HYPP; Canine rhabdomyolysis; Capture myopathy; Compartment
syndrome

Question 16

List three examples of Traumatic myopathies

Answer 16

Downer syndrome; Post-anesthetic myopathy; Crush syndrome (acute trauma

Question 17

List three examples of Inflammatory diseases

Answer 17

• *Bacterial**: Malignant edema; Black leg
• *Parasitic Myositis**: Trichinosis; Cysticercosis; Sarcocystosis; Toxoplasmosis
• *Idiopathic**: Canine Masticatory Myositis; Canine Dermatomyositis

Question 18

List three examples of Primary neoplasia

Answer 18

Rhabdomyoma; Rhabdomyosarcoma

Question 19

1. Atrophy is what type of skeletal muscle pathology?
2. Atrophy is defined as?
3. Is atrophy a reversible or irreversible change?
4. List the three types of atrophy.

Answer 19

1. Disturbance of growth
2. Atrophy is defined as a reduction in muscle size.
3. Reversible.
4. Denervation, disuse, atrophy of cachexia/malnutrition.

Question 20

Denervation (_______) atrophy is characterized by _____ atrophy (half muscle mass in _____).

Long standing denervation may result in ______ and ____ infiltration (______) of affected muscles.

Provide two examples of denervation atrophy.

Answer 20

neurogenic, rapid, weeks, fibrosis, fat, steatosis

Certain viruses damage neurons –> lack of innervation in muscle = example of denervation atrophy.
HBC can have destruction of brachial plexus —> denervation atrophy.

Question 21

In cases of disuse atrophy, innervation is _____ (tonic stimuli). However, atrophy is associated to ________ of a limb or body part because of ____ (fracture, tenotomy, ankylosis etc).

Provide an example of disuse atrophy.

Answer 21

intact, immobilization, pain

Disuse atrophy: breaks leg, twist ankle —> cast for awhile. In a month or two, when take cast off you will see there is a decrease in muscle mass. People that are bed ridden/animals in recumbency for a long period of time due to chronic illness —> disuse muscle atrophy. Fortunately atrophy is reversible so after you have disuse atrophy, once you start exercising again you recover.

Question 22

Atrophy of cachexia/ malnutrition occurs _____ over time and results in the depletion of ____ stores and _____ _____. Type ___ (white, fast twitch) fibers are primarily affected.

Answer 22

slowly, fat, muscle mass, II

Question 23

Label the image below.
This is an example of?

Answer 23

Example of muscle atrophy.

Dorsal view of equine trachea.

Green circle: atrophy of left Crico-arytenoideus. Common in horses; Half of one side if affected. Example of denervation atrophy. Associated with degeneration of laryngeal nerve. Horses during exercise start making sounds due to collapse of that side of the larynx.

Question 24

Hypertrophy is the muscle’s response to ______ work
load (________/________ hypertrophy).
There is an increase in the ____ but not in the _____ of muscle fibers. Can be enhanced by _______ _____.

Answer 24

increased, physiologic, compensatory, size, number, steroidal drugs

Question 25

Hyperplasia is defined as an increase in the ______ of cells. In vet med, we see this in specific breeds of cattle due to a _____ \_\_\_\_\_ of the _______ gene which normally ______ muscle growth. The defect reverses this function, resulting in the _______ of muscle mass. Can also be present in \_\_\_\_. What specific cattle breeds is this defect commonly present in? How does this defect affect muscle fibers? What muscles are specifically effected? What is a potential medical complication of this congenital defect?

Answer 25

number, congenital defect, myostatin, limits, doublign, mice. Charolais, Santa Gertrudis, Angus, Belgian Blue, etc.) There is an increased in the number of muscle fibers which are of normal size and structure, Muscles of the thighs, rump, loin, and shoulder are primarily affected giving these animals a very athletic appearance. Dystocia may occur.

Question 26

These mice suffer from...

Answer 26

Myostatin-lacking, follistatin-overexpressing mouse (right) compared to wild type (left).

Question 27

The animal (define) is an example of...

Answer 27

Belgian Blue Bull, double muscling

Question 28

The animal (define) in this image is suffering from...

Answer 28

Whippet, double-muscling. Whippets can have this inherited condition.

Question 29

Degeneration/ Necrosis is a common sequel to ______ injury regardless of its cause (metabolic, traumatic, chemical, infectious etc.,). Often occurs ______ along the length of the \_\_\_\_. Can be _____ (if there is preservation of the ______ \_\_\_\_\_\_/\_\_\_\_\_\_ _____ and the ________ cells). ________ cells have the capability to replicate and transform into \_\_\_\_\_\_, which would _______ the damaged muscle fibers. In cases of severe injury, ______ will follow. Can be detected _______ only in severe cases: Muscles become ____ and occasionally \_\_\_\_\_; red discoloration may occur in cases in which there is ______ or ______ (release of _____ in the interstitium. Give an example of degeneration.

Answer 29

myofibril, segmentally, myofiber, reversible, basal lamina, basement membrane, satellite, Satellite, myoblasts, replace, necrosis, grossly, pale, calcified, hemorrhage, rhabdomyolysis, myoglobin Exertional myopathies associated with strenuous exercise (especially in wildlife when they are running away from predator/capture) —\> significant clinical disease.

Question 30

1. Describe the image below 2. Hypercontraction of muscle fibers --\> ?

Answer 30

1. Early stages of muscle fiber degeneration/ necrosis. 2. large rounded eosinophilic fibers = degenerating cells, nuclei in periphery and color is normal = healthy cell.

Question 31

**Microscopically** myofiber degeneration is characterized by \_\_\_\_\_\_\_, \_\_\_\_\_\_, loss of _______ and \_\_\_\_\_\_\_\_.

Answer 31

swelling, hyalinization, striations, fragmentation

Question 32

Describe the image below.

Answer 32

Myofiber degeneration. ## Footnote Loss of striations. Play with light, can see striations of sarcomere. Fibers may look swollen, more eosinophilia, sarcoplasm look more eosinophillic.

Question 33

Describe the image below.

Answer 33

Myofiber degeneration. Segmental necrosis. Sample from ahorse with monensin toxicosis.

Question 34

\_\_\_\_\_\_\_\_\_\_ is a common sequel to muscle degeneration and necrosis. In severe cases this change which starts as _______ \_\_\_\_\_\_ overload can be detected ________ : white, chalky gritty ______ scattered throughout the affected muscle.

Answer 34

Calcification, mitochondrial calcium, grossly, foci

Question 35

Describe the image below

Answer 35

In severe cases this change which starts as mitochondrial calcium overload can be detected grossly: white, chalky gritty foci scattered throughout the affected muscle

Question 36

When the affected muscle is undergoing repair, if the injury is **non-disruptive** the basement membrane (basal lamina) will remain _______ and will provide the framework for effective repair. If the injury is **disruptive**, as may occur with ______ \_\_\_\_\_\_ (e.g., laceration, tearing), then repair will not be as efficient, and _______ will occur (part of the damage muscle will be replaced by _______ \_\_\_\_\_\_\_ \_\_\_\_\_).

Answer 36

intact, severe trauma, scarring, fibrous connective tissue

Question 37

In non-disruptive muscle injury, ______ cells proliferate and _______ to the damaged myofiber and become \_\_\_\_\_\_\_\_ which fuse to form __________ \_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_. Myofiber regeneration is completed in \_\_\_-\_\_\_ _____ although central nuclei and nuclear _______ may persist beyond this time.

Answer 37

satellite, migrate, myoblasts, multinucleated cellular bands, 2-3 weeks, rowing

Question 38

What can be seen in the image below? What is different about what is circled in the image below? What is the phenomenon indicative of?

Answer 38

Nuclear rowing: Evidence of myofiber regeneration. nuclear rowing - bluish cytoplasm b/c there is a lot more protein synthesis and therefore pics up more H. past injury

Question 39

Segmental necrosis and regeneration are a \_\_\_\_\_\_\_ response to muscle injury; therefore, their presence alone are not helpful in determining the \_\_\_\_\_. Assessing the ______ and the ______ of the lesions, however, has proven useful in determining the possible _____ of muscle degeneration/necrosis. The concept of whether the lesion is monophasic (DEFINE) or polyphasic (DEFINE), has further improved the diagnostic evaluation of muscle injury.

Answer 39

generalized, cause, distribution, duration, causes, same duration, indicative of a single insult different stages of development, indicative of an ongoing degenerative process

Question 40

A focal monophasic injury would be the result of a _____ \_\_\_\_\_\_ Examples of multifocal monophasic injury?

Answer 40

single incident, IM injection, single episode of strenuous exercise (exertional myopathy), single exposure to a msucle toxin like monensin

Question 41

Describe what can be seen in the image below.

Answer 41

Circle on the left = degeneration/necrosis Circle on the right = regeneration

Question 42

Provide some examples of polyphasic muscle injury.

Answer 42

Example of polyphasic muscle injury are nutritional myopathy (Vit E/ selenium deficiency) and muscular dystrophy → ongoing insult so both degeneration/necrosis and regeneration will be observed at any given time in the affected muscle. multifocal, different stages --\> polyphasic. Could be associated with Vitamin E Selenium deficiency especialy in ruminants and pigs (deficiency with antioxidative factors develop oxidative injury; lipooxidatioon of cell membranes; since in deficient state, this occurs all of the time.