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Questions and Answers
What is the primary function of skeletal muscle myocytes?
What is the primary function of skeletal muscle myocytes?
Muscle dysfunction can only occur due to diseases directly affecting muscle tissue.
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?
What are the three categories of myocytes based on their metabolic usage?
Type I, Type IIa, Type IIb
Myocytes are surrounded by the ________.
Myocytes are surrounded by the ________.
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Match each type of muscle fiber with its primary metabolic usage:
Match each type of muscle fiber with its primary metabolic usage:
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What role do mitochondria play in myocytes?
What role do mitochondria play in myocytes?
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Myocytes can be longer than one meter in larger animals.
Myocytes can be longer than one meter in larger animals.
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What is the term used for the bundles of myocytes separated by fibrous connective tissue?
What is the term used for the bundles of myocytes separated by fibrous connective tissue?
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What type of muscle atrophy occurs due to the severance of a nerve leading to decreased myocyte activity?
What type of muscle atrophy occurs due to the severance of a nerve leading to decreased myocyte activity?
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Muscle hypertrophy can only occur as a result of pathologic conditions.
Muscle hypertrophy can only occur as a result of pathologic conditions.
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What is the primary role of macrophages during muscle injury?
What is the primary role of macrophages during muscle injury?
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If the sarcolemma is not intact after injury, the ends of the myocyte will ______.
If the sarcolemma is not intact after injury, the ends of the myocyte will ______.
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Match the type of muscle atrophy with its cause:
Match the type of muscle atrophy with its cause:
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Which enzyme is specific for skeletal and cardiac muscle for diagnosing muscle damage?
Which enzyme is specific for skeletal and cardiac muscle for diagnosing muscle damage?
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A single significant episode of muscle damage will lead to a persistent increase in CK levels.
A single significant episode of muscle damage will lead to a persistent increase in CK levels.
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What changes in muscle coloration indicate necrosis or degeneration?
What changes in muscle coloration indicate necrosis or degeneration?
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The concept of ______ lesions revolves around whether the damage is present in one location or multiple sites.
The concept of ______ lesions revolves around whether the damage is present in one location or multiple sites.
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Which type of muscle atrophy occurs due to prolonged muscle disuse?
Which type of muscle atrophy occurs due to prolonged muscle disuse?
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Monophasic lesions indicate that all myocytes are in the same stage of repair or degeneration.
Monophasic lesions indicate that all myocytes are in the same stage of repair or degeneration.
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What physiological process helps replace damaged myofibrils in muscle?
What physiological process helps replace damaged myofibrils in muscle?
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Long-nerve degeneration is also known as ______.
Long-nerve degeneration is also known as ______.
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What characterizes multiphasic necrosis in muscle tissue?
What characterizes multiphasic necrosis in muscle tissue?
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What disease can young piglets develop due to iron injections?
What disease can young piglets develop due to iron injections?
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Monensin is safe for all animal species when included in their feed.
Monensin is safe for all animal species when included in their feed.
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What are the histological findings associated with a single large dose of monensin?
What are the histological findings associated with a single large dose of monensin?
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Rhabdomyomas are benign tumors that primarily develop in the ________ muscles of dogs.
Rhabdomyomas are benign tumors that primarily develop in the ________ muscles of dogs.
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Match the following species with the common sites for rhabdomyoma development:
Match the following species with the common sites for rhabdomyoma development:
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What symptoms may follow the ingestion of a single fatal dose of monensin?
What symptoms may follow the ingestion of a single fatal dose of monensin?
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Alcohol is considered a common cause of toxic muscle necrosis in humans.
Alcohol is considered a common cause of toxic muscle necrosis in humans.
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What type of tumors are rhabdomyosarcomas?
What type of tumors are rhabdomyosarcomas?
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Monensin is classified as an ________ antibiotic.
Monensin is classified as an ________ antibiotic.
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Which of the following is a symptom of congestive heart failure caused by sublethal doses of monensin?
Which of the following is a symptom of congestive heart failure caused by sublethal doses of monensin?
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What causes sheep to be infested with Taenia ovis?
What causes sheep to be infested with Taenia ovis?
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Sarcocystosis can cause disease only if small numbers of protozoa invade myocytes.
Sarcocystosis can cause disease only if small numbers of protozoa invade myocytes.
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What is the disease characterized by the body producing antibodies against muscle self-antigens?
What is the disease characterized by the body producing antibodies against muscle self-antigens?
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Dogs develop _______ when antibodies are produced against receptors on the neuromuscular junction.
Dogs develop _______ when antibodies are produced against receptors on the neuromuscular junction.
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Match the following diseases with their characteristics:
Match the following diseases with their characteristics:
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Which of the following is a common symptom of myasthenia gravis in dogs?
Which of the following is a common symptom of myasthenia gravis in dogs?
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Chronic elevation in serum CK activity is not observed in polymyositis.
Chronic elevation in serum CK activity is not observed in polymyositis.
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What disease can cause eosinophilic myositis as a hypersensitivity reaction to encysted protozoa?
What disease can cause eosinophilic myositis as a hypersensitivity reaction to encysted protozoa?
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The adult Taenia ovis resides in the _______ of dogs.
The adult Taenia ovis resides in the _______ of dogs.
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Match the animal with its associated age for peak incidence of white muscle disease:
Match the animal with its associated age for peak incidence of white muscle disease:
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What is the primary cause of white muscle disease?
What is the primary cause of white muscle disease?
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Muscle necrosis in white muscle disease is primarily caused by the failure of the antioxidant system.
Muscle necrosis in white muscle disease is primarily caused by the failure of the antioxidant system.
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What appearance is typically observed in the gross necropsy of muscles affected by white muscle disease?
What appearance is typically observed in the gross necropsy of muscles affected by white muscle disease?
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In advanced cases of white muscle disease, muscles may exhibit _______ due to necrosis.
In advanced cases of white muscle disease, muscles may exhibit _______ due to necrosis.
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What condition is characterized by muscle necrosis in 'downer cows'?
What condition is characterized by muscle necrosis in 'downer cows'?
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Muscle enzymes in serum can help predict whether a cow with muscle damage will stand again.
Muscle enzymes in serum can help predict whether a cow with muscle damage will stand again.
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What is the characteristic smell associated with blackleg?
What is the characteristic smell associated with blackleg?
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Blackleg is caused by multiplication of Clostridium ______ within damaged muscle.
Blackleg is caused by multiplication of Clostridium ______ within damaged muscle.
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Match the following conditions with their causes:
Match the following conditions with their causes:
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Which bacterial species is primarily responsible for gas gangrene?
Which bacterial species is primarily responsible for gas gangrene?
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Cysticercus ovis infects the liver and gallbladder of carnivores.
Cysticercus ovis infects the liver and gallbladder of carnivores.
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What common symptom does renal dysfunction cause in downer cows?
What common symptom does renal dysfunction cause in downer cows?
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Gas gangrene can develop from deep penetrating ______ infected by clostridial bacteria.
Gas gangrene can develop from deep penetrating ______ infected by clostridial bacteria.
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Which viral disease does NOT result in muscle necrosis?
Which viral disease does NOT result in muscle necrosis?
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Clostridial infections lead to vasoconstriction and prevent neutrophils from reaching the bacteria.
Clostridial infections lead to vasoconstriction and prevent neutrophils from reaching the bacteria.
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What is the typical cause of wooden tongue in cattle?
What is the typical cause of wooden tongue in cattle?
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The increase in the activity of muscle enzymes in serum is roughly proportional to the amount of ______.
The increase in the activity of muscle enzymes in serum is roughly proportional to the amount of ______.
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Which of the following is a significant reason for the rapid death of animals with blackleg?
Which of the following is a significant reason for the rapid death of animals with blackleg?
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What causes myoglobinuria in muscle diseases?
What causes myoglobinuria in muscle diseases?
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A longer serum half-life of AST compared to CK indicates that measuring both can help assess muscle disease severity.
A longer serum half-life of AST compared to CK indicates that measuring both can help assess muscle disease severity.
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What is the result of severe myoglobinuria on urine appearance?
What is the result of severe myoglobinuria on urine appearance?
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Hyperkalemia may occur in severe muscle diseases due to the release of the intracellular cation ______.
Hyperkalemia may occur in severe muscle diseases due to the release of the intracellular cation ______.
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Match the muscle disease with its characteristic:
Match the muscle disease with its characteristic:
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Which disease is associated with increased muscle size in calves?
Which disease is associated with increased muscle size in calves?
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Exertional rhabdomyolysis is predominantly seen in pigs.
Exertional rhabdomyolysis is predominantly seen in pigs.
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What is the primary contributing factor in malignant hyperthermia?
What is the primary contributing factor in malignant hyperthermia?
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The only storage disease commonly observed in horses is ______.
The only storage disease commonly observed in horses is ______.
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Match the following conditions with their descriptions:
Match the following conditions with their descriptions:
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What often precedes acute renal failure in myoglobinuria?
What often precedes acute renal failure in myoglobinuria?
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In acute renal failure caused by myoglobinuria, the kidneys typically appear pale and swollen.
In acute renal failure caused by myoglobinuria, the kidneys typically appear pale and swollen.
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Name one common trigger for malignant hyperthermia.
Name one common trigger for malignant hyperthermia.
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Exertional rhabdomyolysis in horses is also known as ______.
Exertional rhabdomyolysis in horses is also known as ______.
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Match the following diseases with their associated clinical signs:
Match the following diseases with their associated clinical signs:
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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?
