Pathology: Skeletal Muscle

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Questions and Answers

What is the primary function of skeletal muscle myocytes?

Storage of nutrients

Regulation of blood flow

Signal transmission

Contraction (correct)

Muscle dysfunction can only occur due to diseases directly affecting muscle tissue.

False

What are the three categories of myocytes based on their metabolic usage?

Type I, Type IIa, Type IIb

Myocytes are surrounded by the ________.

sarcolemma Signup and view all the answers

Match each type of muscle fiber with its primary metabolic usage:

Type I = Oxidative metabolism Type IIa = Combination of oxidative and glycolytic metabolism Type IIb = Glycolytic metabolism Signup and view all the answers

What role do mitochondria play in myocytes?

Energy production Signup and view all the answers

Myocytes can be longer than one meter in larger animals.

True Signup and view all the answers

What is the term used for the bundles of myocytes separated by fibrous connective tissue?

Fascicles Signup and view all the answers

What type of muscle atrophy occurs due to the severance of a nerve leading to decreased myocyte activity?

Denervation atrophy Signup and view all the answers

Muscle hypertrophy can only occur as a result of pathologic conditions.

False Signup and view all the answers

What is the primary role of macrophages during muscle injury?

To remove necrotic material. Signup and view all the answers

If the sarcolemma is not intact after injury, the ends of the myocyte will ______.

bulge Signup and view all the answers

Match the type of muscle atrophy with its cause:

Disuse atrophy = Prolonged muscle immobilization Denervation atrophy = Nerve transection Atrophy due to cachexia = Malnutrition or neoplasia Hypertrophy = Increased workload Signup and view all the answers

Which enzyme is specific for skeletal and cardiac muscle for diagnosing muscle damage?

Creatine kinase (CK) Signup and view all the answers

A single significant episode of muscle damage will lead to a persistent increase in CK levels.

False Signup and view all the answers

What changes in muscle coloration indicate necrosis or degeneration?

Paleness due to blood squeezing out. Signup and view all the answers

The concept of ______ lesions revolves around whether the damage is present in one location or multiple sites.

focal Signup and view all the answers

Which type of muscle atrophy occurs due to prolonged muscle disuse?

Disuse atrophy Signup and view all the answers

Monophasic lesions indicate that all myocytes are in the same stage of repair or degeneration.

True Signup and view all the answers

What physiological process helps replace damaged myofibrils in muscle?

Satellite cell activity. Signup and view all the answers

Long-nerve degeneration is also known as ______.

distal axonopathy Signup and view all the answers

What characterizes multiphasic necrosis in muscle tissue?

Different stages of degeneration and repair present in myocytes. Signup and view all the answers

What disease can young piglets develop due to iron injections?

White muscle disease Signup and view all the answers

Monensin is safe for all animal species when included in their feed.

False Signup and view all the answers

What are the histological findings associated with a single large dose of monensin?

Multifocal monophasic necrosis Signup and view all the answers

Rhabdomyomas are benign tumors that primarily develop in the ________ muscles of dogs.

laryngeal Signup and view all the answers

Match the following species with the common sites for rhabdomyoma development:

Dogs = Laryngeal muscles Pigs = Heart Cattle = Heart Sheep = Heart Signup and view all the answers

What symptoms may follow the ingestion of a single fatal dose of monensin?

Diarrhea and colic Signup and view all the answers

Alcohol is considered a common cause of toxic muscle necrosis in humans.

True Signup and view all the answers

What type of tumors are rhabdomyosarcomas?

Malignant myocytic tumors Signup and view all the answers

Monensin is classified as an ________ antibiotic.

ionophore Signup and view all the answers

Which of the following is a symptom of congestive heart failure caused by sublethal doses of monensin?

Rapid respiratory rate Signup and view all the answers

What causes sheep to be infested with Taenia ovis?

Ingesting eggs in dog feces Signup and view all the answers

Sarcocystosis can cause disease only if small numbers of protozoa invade myocytes.

False Signup and view all the answers

What is the disease characterized by the body producing antibodies against muscle self-antigens?

Polymyositis Signup and view all the answers

Dogs develop _______ when antibodies are produced against receptors on the neuromuscular junction.

Myasthenia gravis Signup and view all the answers

Match the following diseases with their characteristics:

Polymyositis = Body produces antibodies against self-antigens Masticatory muscle myositis = Autoantibodies against type II myosin Myasthenia gravis = Antibodies against neuromuscular junction receptors White muscle disease = Nutritional myopathy due to Vitamin E/Selenium deficiency Signup and view all the answers

Which of the following is a common symptom of myasthenia gravis in dogs?

Rapid fatigue during exercise Signup and view all the answers

Chronic elevation in serum CK activity is not observed in polymyositis.

False Signup and view all the answers

What disease can cause eosinophilic myositis as a hypersensitivity reaction to encysted protozoa?

Sarcocystosis Signup and view all the answers

The adult Taenia ovis resides in the _______ of dogs.

gastrointestinal tract Signup and view all the answers

Match the animal with its associated age for peak incidence of white muscle disease:

Calves = 4 to 6 weeks old Lambs = 2 to 3 weeks old Pigs = 6 to 20 weeks old Adult Sheep = Rarely affected Signup and view all the answers

What is the primary cause of white muscle disease?

Dietary deficiency of Vitamin E/Selenium Signup and view all the answers

Muscle necrosis in white muscle disease is primarily caused by the failure of the antioxidant system.

True Signup and view all the answers

What appearance is typically observed in the gross necropsy of muscles affected by white muscle disease?

Swelling and pallor of muscles Signup and view all the answers

In advanced cases of white muscle disease, muscles may exhibit _______ due to necrosis.

mineralization Signup and view all the answers

What condition is characterized by muscle necrosis in 'downer cows'?

Traumatic muscle damage Signup and view all the answers

Muscle enzymes in serum can help predict whether a cow with muscle damage will stand again.

True Signup and view all the answers

What is the characteristic smell associated with blackleg?

'Rancid butter' Signup and view all the answers

Blackleg is caused by multiplication of Clostridium ______ within damaged muscle.

chauvoei Signup and view all the answers

Match the following conditions with their causes:

Blackleg = Clostridium chauvoei Gas gangrene = Clostridium perfringens Wooden tongue = Actinobacillus lignieresii Cysticercosis = Cysticercus ovis Signup and view all the answers

Which bacterial species is primarily responsible for gas gangrene?

Clostridium perfringens Signup and view all the answers

Cysticercus ovis infects the liver and gallbladder of carnivores.

False Signup and view all the answers

What common symptom does renal dysfunction cause in downer cows?

Increased serum urea Signup and view all the answers

Gas gangrene can develop from deep penetrating ______ infected by clostridial bacteria.

wounds Signup and view all the answers

Which viral disease does NOT result in muscle necrosis?

Cysticercosis Signup and view all the answers

Clostridial infections lead to vasoconstriction and prevent neutrophils from reaching the bacteria.

True Signup and view all the answers

What is the typical cause of wooden tongue in cattle?

Infection after cuts on the tongue Signup and view all the answers

The increase in the activity of muscle enzymes in serum is roughly proportional to the amount of ______.

muscle damage Signup and view all the answers

Which of the following is a significant reason for the rapid death of animals with blackleg?

Toxemia from bacterial toxins Signup and view all the answers

What causes myoglobinuria in muscle diseases?

Release of myoglobin from damaged muscle cells Signup and view all the answers

A longer serum half-life of AST compared to CK indicates that measuring both can help assess muscle disease severity.

True Signup and view all the answers

What is the result of severe myoglobinuria on urine appearance?

Brown discoloration Signup and view all the answers

Hyperkalemia may occur in severe muscle diseases due to the release of the intracellular cation ______.

potassium Signup and view all the answers

Match the muscle disease with its characteristic:

Myoglobinuria = Brown urine discoloration Malignant hyperthermia = Continuous muscle contraction Exertional rhabdomyolysis = Stiffness and pain during exercise Capture myopathy = Necrosis due to prolonged muscle activity Signup and view all the answers

Which disease is associated with increased muscle size in calves?

Congenital muscular hypertrophy Signup and view all the answers

Exertional rhabdomyolysis is predominantly seen in pigs.

False Signup and view all the answers

What is the primary contributing factor in malignant hyperthermia?

Genetic defects in the ryanodine receptor Signup and view all the answers

The only storage disease commonly observed in horses is ______.

polysaccharide storage myopathy Signup and view all the answers

Match the following conditions with their descriptions:

Splayleg = Inability to place legs under body Capture myopathy = Necrosis from prolonged muscle activity Myoglobinuria = Kidneys stained by myoglobin Malignant hyperthermia = Triggered by stress or halothane anesthesia Signup and view all the answers

What often precedes acute renal failure in myoglobinuria?

Myoglobin toxicity to renal tubular cells Signup and view all the answers

In acute renal failure caused by myoglobinuria, the kidneys typically appear pale and swollen.

True Signup and view all the answers

Name one common trigger for malignant hyperthermia.

Stress or halothane anesthesia Signup and view all the answers

Exertional rhabdomyolysis in horses is also known as ______.

tying up Signup and view all the answers

Match the following diseases with their associated clinical signs:

Exertional rhabdomyolysis = Stiffness and pain during or after exercise Capture myopathy = Swollen and pale thigh muscles Malignant hyperthermia = Pale and cooked appearance of muscles Polysaccharide storage myopathy = Increased susceptibility to exertional rhabdomyolysis Signup and view all the answers

Study Notes

Pathogenesis and Diagnosis of Skeletal Muscle Diseases

Muscle dysfunction can arise not only from primary muscle diseases but also from secondary conditions affecting other organ systems (e.g., nervous, endocrine).
Muscle diseases are more prevalent in horses and food animals compared to companion animals.

Normal Histology and Function of Skeletal Muscle

Myocyte: the functional unit of muscle, characterized by long, narrow cells with multiple peripheral nuclei.
Myofibres: another term for myocytes; can exceed 1 meter in length in larger animals.
Myocytes contain large amounts of mitochondria for energy due to their role in contraction.
Three types of myocytes:
- Type I (slow twitch): use oxidative metabolism.
- Type IIa (fast twitch): utilize both oxidative and glycolytic metabolism.
- Type IIb (fast twitch): rely solely on glycolytic metabolism.
The neuron innervating each myocyte determines its type, leading to uneven disease effects within muscle.

Muscle Response to Injury

Damage often localized due to the long structure of myocytes; repair processes depend on sarcolemma integrity.
If the sarcolemma is intact, macrophages remove necrotic material, and satellite cells produce replacement myofibrils.
Disruption of the sarcolemma leads to greater damage; extensive defects result in fibrous tissue replacement rather than restoration of myocyte function.
Degeneration causes muscles to appear pale due to swelling and blood squeeze.

Muscle Size Changes

Changes in muscle size occur through atrophy or hypertrophy due to the inability of myocytes to divide.
Denervation atrophy occurs from significant nerve damage, resulting in rapid muscle size reduction.
Disuse atrophy correlates with muscle immobilization but is usually reversible.
Cachexia results in muscle wasting due to malnutrition or disease.
Hypertrophy can be physiological (response to increased workload) or pathological (disease-induced).

Laboratory Diagnosis of Muscle Disease

Increased serum levels of creatine kinase (CK) and aspartate aminotransferase (AST) indicate myofibre degeneration or necrosis.
CK is specific to skeletal and cardiac muscle; its short half-life means it decreases within 24-48 hours post-damage.
AST lacks specificity, thus combined measurement with CK provides better insight into muscle disease severity.
Myoglobinuria indicates severe muscle damage and may cause renal failure.
Hyperkalemia can accompany significant muscle diseases.

Congenital and Genetic Disorders

Congenital muscular hypertrophy: common in calves, resulting in increased muscle size and potential dystocia.
Splayleg in pigs/swimmer puppies: genetic conditions lead to leg mobility issues; typically self-resolving.
Malignant hyperthermia: genetic disorder triggered by stress or anesthesia, causing continuous muscle contraction and necrosis.
Storage diseases, notably polysaccharide storage myopathy in horses, increase the risk of exertional rhabdomyolysis.

Environmental and Physical Diseases

Exertional rhabdomyolysis: also known as "tying up," characterized by muscle stiffness and swelling after exercise, primarily affecting horses.
Capture myopathy results from prolonged stress-related muscle contractions, leading to necrosis; affected animals may die from metabolic acidosis.
Trauma-induced muscle damage can arise from factors like downer cow syndrome due to hypoxia from weight occlusion on limbs.

Infectious Diseases

Viruses like blue-tongue or foot-and-mouth can cause skeletal muscle necrosis, though absent in New Zealand.
Clostridial infections, such as blackleg and gas gangrene, thrive in damaged muscle areas, causing rapid necrosis and often leading to fatal toxemia.
Gas gangrene develops after deep wounds provoke anaerobic bacterial growth, frequently resulting in a foul odor and pronounced tissue necrosis.
Wooden tongue is characterized by infection after tongue injuries, primarily affecting cattle.### Tapeworms and Cysticercus ovis
Tapeworms live in the intestines of carnivores and in the muscles of prey species.
Cysticercus ovis causes sheep measles, residing in the heart and skeletal muscle of sheep and goats.
Transmission to sheep occurs by ingesting eggs in dog feces; dogs are infested by consuming infected, uncooked sheep meat.
Adult tapeworm Taenia ovis exists in the gastrointestinal tract of dogs.
A historical decrease in T. ovis prevalence corresponds to effective hydatid control measures.
A recent resurgence of sheep measles is noted as hydatid controls have relaxed.
Necropsy shows numerous white foci in affected sheep's muscle, with mild fibrosis and inflammatory cells observed histologically.

Sarcocystosis

Caused by protozoa requiring two hosts for their lifecycle; intermediate hosts ingest protozoa that multiply asexually in the bloodstream.
Protozoa invade skeletal muscle, with definitive hosts infected by consuming infected muscle.
Sarcocystosis is usually asymptomatic but can cause disease if protozoa invade myocytes in large numbers.
Eosinophilic myositis may occur due to hypersensitivity reactions against encysted protozoa, resulting in inflammation.

Immune-Mediated Diseases

Polymyositis: Most common in dogs, characterized by antibody production against muscle self-antigens. Leads to muscle pain, swelling, and atrophy. Elevated serum CK levels are noted.
Masticatory Muscle Myositis: Also known as eosinophilic myositis. Triggered by autoantibodies against masticatory myosin, leading to muscle pain and atrophy. Acute biopsy shows myocyte necrosis with eosinophil inflammation; chronic lesions present with fibrosis.
Myasthenia Gravis: Antibodies target receptors at the neuromuscular junction, causing exercise-induced fatigue. Affected dogs may also develop megaesophagus. Some cases are linked to thymomas.

Nutritional Disorders and Toxicities

Vitamin E/Selenium Deficiency: Commonly causes white muscle disease, particularly in young herbivores (pigs, cattle, sheep). Linked to diets lacking these antioxidants which protect against free radical damage.
Muscle necrosis typically affects the tongue, diaphragm, and heart in younger animals; older ones show lesions in thigh and shoulder muscles.
Monensin Toxicosis: Results in necrosis of skeletal and cardiac muscle, with sensitivity varying across species. Horses are the most sensitive, with fatal doses leading to colic and death.
Muscle damage is due to ion disruption by monensin, a common feed additive.

Neoplastic and Non-Neoplastic Tumors

Muscle tumors can arise from myocytes, endothelial, or fibroblastic origins, with the latter two being more common.
Rhabdomyomas: Benign tumors of skeletal myocytes, commonly found in the laryngeal muscles of dogs and in the hearts of pigs, cattle, and sheep.
Rhabdomyosarcomas: Malignant tumors that are aggressive and metastatic, often found in appendicular skeletal muscles and in younger dogs' bladders, forming "bunches of grapes" known as botryoid rhabdomyosarcomas.

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Test your knowledge on skeletal muscle myocytes and their functions. This quiz covers muscle dysfunction, the categories of myocytes based on metabolism, and the role of mitochondria in muscle cells. Ready to challenge your understanding of muscle physiology?