Skeletal Muscle

Question 1

Myopathy:

Answer 1

Disorder of muscle

Question 2

Muscular dystophy (2):

Answer 2

• Inherited disorder

- Progressive muscle weakness and wasting

Question 3

Segmental muscle necrosis:

Answer 3

Destruction of a portion of the myocyte length

Question 4

Muscular regeneration:

Answer 4

Satellite cells reconstitute destroyed muscle

Question 5

Myotonia:

Answer 5

Tonic spasm of one or more muscles

Question 6

Hypotonia:

Answer 6

Deficient tone or tension

Question 7

Athrogryposis:

Answer 7

Fixation of joints in an extended or flexed position

Question 8

Gower’s sign (2):

Answer 8

• Uses the hands and arms to “walk” up from a squatting position
• Indicates weakness of the proximal muscles

Question 9

Muscle type is determined by:

Answer 9

Innervating motor neuron

Question 10

Fiber type grouping:

Answer 10

Neuron/axon drop out leads to larger motor units (muscle fibers per neuron)

Question 11

Grouped atrophy:

Answer 11

Loss of a motor neuron leads to atrophy of associated muscle

Question 12

Denervation atrophy (3):

Answer 12

• Disorder of motor neurons
• Breakdown of myosin and actin
• Resorption of myofibrils

Question 13

Spinal muscular atrophy (3):

Answer 13

• Progressive destruction of anterior horn cells and cranial nerve motor neurons
• Autosomal recessive
• Survival motor neuron 1 (SMN1)

Question 14

Muscular dystrophy pathology (4):

Answer 14

• Variation in fiber size
• Internal nuclei
• Degeneration, necrosis, phagocytosis of fibers
• Later replaced by fibrofatty tissue

Question 15

Duchenne MD (3):

Answer 15

• Dystrophin protein defect
• X-linked
• Most common type of MD

Question 16

Duchenne MD clinical (5):

Answer 16

• Normal at birth
• Delayed walking then clumsy
• Weak pelvic then shoulder girdle
• Pseudohypertorphy of calves
• Impaired cognition

Question 17

Becker MD:

Answer 17

Defect in dystrophin quality/quantity of protein from an abnormal gene at X

Question 18

Facioscapulohumeral MD (3):

Answer 18

• Facial weakness
• Wasting of the upper arm and shoulder muscles
• The scapular bones look like wings when the arms are raised

Question 19

Emery-Dreifuss MD (3):

Answer 19

• Early on humeroperoneal weakness
• Prominent contractures especially elbows and ankles
• Cardiomyopathy

Question 20

Myotonic dystrophy (6):

Answer 20

• Myotonia
• Childhood onset
• Facial muscle atrophy and ptosis
• Cataracts
• Autosomal dominant
• Anticipation

Question 21

Malignant hyperpyrexia (5):

Answer 21

Malignant hyperthermia

• Ryanodine receptor RyR1
• Sudden hypermetabolic state with tachypnea
• Triggered by anesthesia
• Release of calcium from sarcoplasmic reticulum
• Tx: dantrolene

Question 22

Central core disease (4):

Answer 22

• Autosomal dominant
• Hypotonia
• Ryanodine receptor 1 (RYR1)
• Risk for malignant hyperthermia

Question 23

Nemaline myopathy (4):

Answer 23

• Nonprogressive hypotonia, weakness
• Delayed development in kids
• Involves proximal limb muscle
• Subsarcolemmal spindle-shaped particles from Z-band material

Question 24

Lipid myopathies (3):

Answer 24

• Accumulate lipid in myocytes
• Defects in carnitine transport system
• Defects in mitochondrial dehydrogenase enzyme system

Question 25

Noninfectious inflammatory myopathies (3):

Answer 25

• Dermatomyositis
• Polymyositis
• Inclusion body myositis

Question 26

Dermatomyositis (4):

Answer 26

• Skin rash precedes or begins with myositis
• Muscle weakness +/- myalgias
• Early proximal muscles; late distal muscles
• Up to 25% have cancer

Question 27

Dermatomyositis pathology:

Answer 27

Microvasculature attacked by antibodies and compliment creating ischemia

Question 28

Polymyositis (4):

Answer 28

• Systemic inflammatory myopathy
• Muscle weakness +/- myalgias
• Autoantibodies against tRNA synthetases
• Cytotoxic CD8+ T cells in endomysium destroy muscle

Question 29

Inclusion body myositis (4):

Answer 29

• Begins insidiously; > 50 years old
• Begins with distal muscles
• CD8+ cytotoxic cells
• No response to immunosuppression

Question 30

Hypothyroidism myopathy (5):

Answer 30

• Cramping/aching muscle; slow movements
• Slow reflexes
• Proximal weakness (posterior neck)
• Elevated CK
• Fiber atrophy

Question 31

Myasthenia Gravis (4):

Answer 31

• Neuromuscular junction disease
• Often begins with extraocular muscle weakness
• Immune-mediated loss of acetylcholine receptors
• Decremental decrease in muscle response to repeated stimulus

Question 32

Lambert-Eaton Myasthenic syndrome (5):

Answer 32

• 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