Skeletal Muscle Flashcards
Myopathy:
Disorder of muscle
Muscular dystophy (2):
- Inherited disorder
- Progressive muscle weakness and wasting
Segmental muscle necrosis:
Destruction of a portion of the myocyte length
Muscular regeneration:
Satellite cells reconstitute destroyed muscle
Myotonia:
Tonic spasm of one or more muscles
Hypotonia:
Deficient tone or tension
Athrogryposis:
Fixation of joints in an extended or flexed position
Gower’s sign (2):
- Uses the hands and arms to “walk” up from a squatting position
- Indicates weakness of the proximal muscles
Muscle type is determined by:
Innervating motor neuron
Fiber type grouping:
Neuron/axon drop out leads to larger motor units (muscle fibers per neuron)
Grouped atrophy:
Loss of a motor neuron leads to atrophy of associated muscle
Denervation atrophy (3):
- Disorder of motor neurons
- Breakdown of myosin and actin
- Resorption of myofibrils
Spinal muscular atrophy (3):
- Progressive destruction of anterior horn cells and cranial nerve motor neurons
- Autosomal recessive
- Survival motor neuron 1 (SMN1)
Muscular dystrophy pathology (4):
- Variation in fiber size
- Internal nuclei
- Degeneration, necrosis, phagocytosis of fibers
- Later replaced by fibrofatty tissue
Duchenne MD (3):
- Dystrophin protein defect
- X-linked
- Most common type of MD
Duchenne MD clinical (5):
- Normal at birth
- Delayed walking then clumsy
- Weak pelvic then shoulder girdle
- Pseudohypertorphy of calves
- Impaired cognition
Becker MD:
Defect in dystrophin quality/quantity of protein from an abnormal gene at X
Facioscapulohumeral MD (3):
- Facial weakness
- Wasting of the upper arm and shoulder muscles
- The scapular bones look like wings when the arms are raised
Emery-Dreifuss MD (3):
- Early on humeroperoneal weakness
- Prominent contractures especially elbows and ankles
- Cardiomyopathy
Myotonic dystrophy (6):
- Myotonia
- Childhood onset
- Facial muscle atrophy and ptosis
- Cataracts
- Autosomal dominant
- Anticipation
Malignant hyperpyrexia (5):
Malignant hyperthermia
- Ryanodine receptor RyR1
- Sudden hypermetabolic state with tachypnea
- Triggered by anesthesia
- Release of calcium from sarcoplasmic reticulum
- Tx: dantrolene
Central core disease (4):
- Autosomal dominant
- Hypotonia
- Ryanodine receptor 1 (RYR1)
- Risk for malignant hyperthermia
Nemaline myopathy (4):
- Nonprogressive hypotonia, weakness
- Delayed development in kids
- Involves proximal limb muscle
- Subsarcolemmal spindle-shaped particles from Z-band material
Lipid myopathies (3):
- Accumulate lipid in myocytes
- Defects in carnitine transport system
- Defects in mitochondrial dehydrogenase enzyme system
Noninfectious inflammatory myopathies (3):
- Dermatomyositis
- Polymyositis
- Inclusion body myositis
Dermatomyositis (4):
- Skin rash precedes or begins with myositis
- Muscle weakness +/- myalgias
- Early proximal muscles; late distal muscles
- Up to 25% have cancer
Dermatomyositis pathology:
Microvasculature attacked by antibodies and compliment creating ischemia
Polymyositis (4):
- Systemic inflammatory myopathy
- Muscle weakness +/- myalgias
- Autoantibodies against tRNA synthetases
- Cytotoxic CD8+ T cells in endomysium destroy muscle
Inclusion body myositis (4):
- Begins insidiously; > 50 years old
- Begins with distal muscles
- CD8+ cytotoxic cells
- No response to immunosuppression
Hypothyroidism myopathy (5):
- Cramping/aching muscle; slow movements
- Slow reflexes
- Proximal weakness (posterior neck)
- Elevated CK
- Fiber atrophy
Myasthenia Gravis (4):
- Neuromuscular junction disease
- Often begins with extraocular muscle weakness
- Immune-mediated loss of acetylcholine receptors
- Decremental decrease in muscle response to repeated stimulus
Lambert-Eaton Myasthenic syndrome (5):
- Neuromuscular junction disorder
- Usually paraneoplastic: small cell carcinoma of lung
- Proximal weakness and autonomic dysfunction
- Antibodies inhibit presynaptic calcium channel and block acetylcholine release
- Enhanced neurotransmission with repetitive stimulation
