PNS

Question 1

Muscle cells

Answer 1

Postmitotic cells
Reserve cells capable of regeneration
Contractile proteins
Long, extensible

Question 2

Neuromuscular junction

Answer 2

Site of contact between motor neuron axon terminal and muscle fiber
Presynaptic terminal releases Ach - binds and depolarizes muscle

Question 3

Type 1 fibers

Answer 3

Slow fibers
White
Rapid, short movements
Rich in oxidative enzymes
Sustained contractions, fatigue resistant

Question 4

Type II fibers

Answer 4

Fast fibers
Red
Protracted control
Rich in glycogen

Question 5

Denervation

Answer 5

Nerve and fibers form motor unit
When it denervated, fibers atrophy
Can be reinnervated from adjacent nerves - nerve group decides what type of fibers

Question 6

Function of muscle cells depends on (2)

Answer 6

1. Proteins in the muscle membrane

2. Generation of ATP from lipid and glycogen in the mitochondria

Question 7

Creatine kinase

Answer 7

Destruction of muscle fibers can be characterized by release of CK

Question 8

Neurogenic atrophy

Answer 8

Form of muscle cell atrophy caused by injury to motor nerves
Atrophic fibers appear angulated
If proximal part of axon is preserved, transection of larger nerves can be repaired
Upper motor neuron: central cortex
Lower motor neuron: spinal cord

Question 9

Guillain-Barré disease

Answer 9

Autoimmune neuritis - attack on motor nerve axons
Develops 2-4 weeks after viral or bacterial infection
Leads to limb weakness and total paralysis
Treated with immunosupressors and plasmapheresis

Question 10

Extent of nerve loss in neurogenic atrophy (2)

Answer 10

1. Single muscle atrophy

2. Fascicular loss (entire nerve is transected)

Question 11

Wallerian degeneration

Answer 11

Neurogenic atrophy

Nerve distal to transection injury degenerates

Question 12

Myasthenia gravis

Answer 12

Autoimmune disease involving neuromuscular junction
Rare
Antibodies to ACh receptors in 85%
In younger group, associated with enlarged thymus - thymoma making antibodies
Striated muscles look normal
Decrease in AChR
Death from respiratory paralysis

Question 13

Involvement of facial muscles in Myasthenia gravis

Answer 13

Ptosis and inability to chew
Double vision (diplopia)
Bland expression

Question 14

Diagnosis of Myasthenia gravis

Answer 14

Anticholinesterase test (transient increased levels of ACh reverses myasthenia)
Blocks enzyme that breaks down Ach-esterase
Electromyography
Serologic testing for antibodies

Question 15

Muscular dystrophies

Answer 15

Genetic defects inherited as Mendelian traits
Primary muscle cell pathology
Progressive course
Onset in childhood, adolescence, or adulthood
Limited diagnostic value of muscle biopsy
Elevated CK levels in blood

Question 16

Duchenne’s Muscular Dystrophy

Answer 16

Most common
Complete deficiency of dystrophin
X-linked recessive in boys
Hypertrophy, fiber splitting, replacement with scar tissue and fat

Question 17

Becker’s dystrophy

Answer 17

Partial deficiency of dystrophin

Question 18

Clinical features of Duchenne’s MD

Answer 18

Weakness of pelvic girdle muscles
Diagnoses from elevated CK, muscle biopsy, molecular testing
Confined to wheelchair
Early death - respiratory insufficiency

Question 19

Myotonic dystrophy

Answer 19

Second most common genetic muscle disease
Autosomal dominant
CTG trinucleotide repeat expansion in the DMOK gene on Chr 19
Symptoms appear in adults

Question 20

Symptoms of Myotonic dystrophy

Answer 20

Myotonia, hatchet face, weakness of eye muscles, systemic symptoms
Ptosis and frontal balding
Multisystem disease: diabetes, heart disease, gonadal atrophy

Question 21

Congenital myopathies

Answer 21

Rare, muscle weakness in infancy - floppy infant syndrome)
Often lethal at early age
Includes lipid, glycogen storage disorders, mitochondrial myopathies, channelopathies, specific myopathies

Question 22

Acquired myopathies

Answer 22

Muscle weakness secondary to systemic disease

Thyroid myopathy, rheumatoid arthritis, diabetic myopathy, cancer myopathy

Question 23

Myositis (2)

Answer 23

1. Infectious

2. Immune

Question 24

Infectious myositis

Answer 24

Pyogenic bacteria - muscle abscess
Anaerobic bacteria
Viruses
Protozoa
Worms

Question 25

Immune myositis

Answer 25

More common
Polymyositis
Dermatomyositis
Systemic lupus erythematosus
Sarcoidosis

Question 26

Clinical features of immune disorders

Answer 26

Myalgia and muscle weakness
Proximal muscles
Elevated CK
Elevated antinuclear antibodies
EMG shoes myopathic changes
Muscle biopsy establishes diagnosis
Treat with steroids or immunosuppressives

Question 27

Pathology of immune disorders (2)

Answer 27

1. Polymyositis

2. Dermatomyositis/SLE

Question 28

Polymyositis

Answer 28

T cells and macrophages
Invade the endomysium
Necrotic and regenerating fibers

Question 29

Dematomyositis/SLE

Answer 29

Cells invade blood vessels in the perimysium
Perifascular atrophy
Lilac blue rash of upper eyelids

Question 30

Soft tissue tumors (3)

Answer 30

1. Benign
2. Locally invasive/low grade
3. Malignant

Question 31

Benign soft tissue tumors (3)

Answer 31

1. Rhabdomyoma
2. Lipoma
3. Fibroma

Question 32

Locally invasive/low grade soft tissue tumors (2)

Answer 32

Often reoccur, do not metastasize

1. Desmoid tumor
2. Fibromatoses

Question 33

Malignant soft tissue tumors (3)

Answer 33

1. Rhabdomyosarcoma
2. Synovial sarcoma
3. Liposarcoma