PNS Flashcards
Muscle cells
Postmitotic cells
Reserve cells capable of regeneration
Contractile proteins
Long, extensible
Neuromuscular junction
Site of contact between motor neuron axon terminal and muscle fiber
Presynaptic terminal releases Ach - binds and depolarizes muscle
Type 1 fibers
Slow fibers White Rapid, short movements Rich in oxidative enzymes Sustained contractions, fatigue resistant
Type II fibers
Fast fibers
Red
Protracted control
Rich in glycogen
Denervation
Nerve and fibers form motor unit
When it denervated, fibers atrophy
Can be reinnervated from adjacent nerves - nerve group decides what type of fibers
Function of muscle cells depends on (2)
- Proteins in the muscle membrane
2. Generation of ATP from lipid and glycogen in the mitochondria
Creatine kinase
Destruction of muscle fibers can be characterized by release of CK
Neurogenic atrophy
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
Guillain-Barré disease
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
Extent of nerve loss in neurogenic atrophy (2)
- Single muscle atrophy
2. Fascicular loss (entire nerve is transected)
Wallerian degeneration
Neurogenic atrophy
Nerve distal to transection injury degenerates
Myasthenia gravis
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
Involvement of facial muscles in Myasthenia gravis
Ptosis and inability to chew
Double vision (diplopia)
Bland expression
Diagnosis of Myasthenia gravis
Anticholinesterase test (transient increased levels of ACh reverses myasthenia)
Blocks enzyme that breaks down Ach-esterase
Electromyography
Serologic testing for antibodies
Muscular dystrophies
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
Duchenne’s Muscular Dystrophy
Most common
Complete deficiency of dystrophin
X-linked recessive in boys
Hypertrophy, fiber splitting, replacement with scar tissue and fat
Becker’s dystrophy
Partial deficiency of dystrophin
Clinical features of Duchenne’s MD
Weakness of pelvic girdle muscles
Diagnoses from elevated CK, muscle biopsy, molecular testing
Confined to wheelchair
Early death - respiratory insufficiency
Myotonic dystrophy
Second most common genetic muscle disease
Autosomal dominant
CTG trinucleotide repeat expansion in the DMOK gene on Chr 19
Symptoms appear in adults
Symptoms of Myotonic dystrophy
Myotonia, hatchet face, weakness of eye muscles, systemic symptoms
Ptosis and frontal balding
Multisystem disease: diabetes, heart disease, gonadal atrophy
Congenital myopathies
Rare, muscle weakness in infancy - floppy infant syndrome)
Often lethal at early age
Includes lipid, glycogen storage disorders, mitochondrial myopathies, channelopathies, specific myopathies
Acquired myopathies
Muscle weakness secondary to systemic disease
Thyroid myopathy, rheumatoid arthritis, diabetic myopathy, cancer myopathy
Myositis (2)
- Infectious
2. Immune
Infectious myositis
Pyogenic bacteria - muscle abscess Anaerobic bacteria Viruses Protozoa Worms
Immune myositis
More common Polymyositis Dermatomyositis Systemic lupus erythematosus Sarcoidosis
Clinical features of immune disorders
Myalgia and muscle weakness Proximal muscles Elevated CK Elevated antinuclear antibodies EMG shoes myopathic changes Muscle biopsy establishes diagnosis Treat with steroids or immunosuppressives
Pathology of immune disorders (2)
- Polymyositis
2. Dermatomyositis/SLE
Polymyositis
T cells and macrophages
Invade the endomysium
Necrotic and regenerating fibers
Dematomyositis/SLE
Cells invade blood vessels in the perimysium
Perifascular atrophy
Lilac blue rash of upper eyelids
Soft tissue tumors (3)
- Benign
- Locally invasive/low grade
- Malignant
Benign soft tissue tumors (3)
- Rhabdomyoma
- Lipoma
- Fibroma
Locally invasive/low grade soft tissue tumors (2)
Often reoccur, do not metastasize
- Desmoid tumor
- Fibromatoses
Malignant soft tissue tumors (3)
- Rhabdomyosarcoma
- Synovial sarcoma
- Liposarcoma
