Transcript Document 7508653

Review of Musculoskeletal
System
Chapter 18
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Muscle
• Skeletal muscle
• > 600 muscles in body
• Fascia
– Epimysium – forms tendons at ends
– Perimysium – divides into fascicles
– Endomysium – surrounds individual fibers
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Motor Unit
• One motor neuron and all the muscle
fibers it innervates
• recruitment
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Muscle cell structure
• Sarcolemma
motor end plate
transverse ( t- ) tubules
• Sarcoplasm
• Sarcoplasmic Reticulum – Stores Ca++
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• Proteins:
– Thick filaments – myosin
– Thin filaments – actin
• Troponin
• Tropomyosin
– Sliding Filament Model
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Muscular Dystrophy
• Group of rare diseases characterized by a
genetic etiology and progressive
degeneration of skeletal muscle.
• X-linked recessive defect
• Most common of the muscular dystrophies
• 1 in 3,000 live births
• Affects males
• Gene located on the short arm of the X
chromosome.
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• 30% of cases arise as a new mutation
• Can be diagnosed immediately after birth
by high serum creatine kinase
• Muscle weakness and delayed motor skills
can be detected early – obvious by age 5
• Age 10 – require leg bracing
• Age 12 – wheelchair
• Age 15 completely bedridden
• Death by 20 – 30 of cardiac arrest or
respiratory failure.
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• Fibrosis → contracture distorts skeletal
development
– Lordosis
– Scoliosis
– Compromised respiration
• Respiratory insufficiency
– Respiratory infection
• Cardiac muscle
– Dysrythmias
– Congestive heart failure
• Mental sluggishness
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• Dystrophin is lacking
– Membrane damage
– Replaced by fibrous connective tissue and
fatty deposits
• Therapy
– Sustain mobility
– Sustain respiratory function
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Myesthenia gravis
• Autoimmune disease in which antibodies
(IgG) bind with acetylcholine receptors on
muscle cells.
• Reduces the number of acetylcholine
receptors at the neuromuscular junction
• Characterized by muscle weakness and
fatigability
• Also associated with other autoimmune
disorders, such as SLE, rheumatoid
arthritis, and thyrotoxicosis
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• In 10-25% of people with MG thymic
tumors are found
– More common in males than females
• 70 – 80 % have pathologic changes in the
thymus
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Classification of myasthenia
• Neonatal myasthenia
– Transitory condition in which 10-15 % of
infants born to mothers with MG show
symptoms of the disease
• Congenital myasthenia
• Juvenile myasthenia – onset us.about 10
years
• Ocular myasthenia
– More common in males
– Weakness of eye muscles and eyelids, may
also include swallowing difficulties and slurred
speech
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• Generalized autoimmune myasthenia
– Involves proximal musculature throughout the
body, and has several courses:
• A course with periodic remissions
• Slowly progressive course
• Rapidly progressive course
• Fulminating course
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Pathophysiology
• Defect in the nerve impulse transmission at
the NMJ
• Postsynaptic acetylcholine receptors are no
longer recognized as “self” and antibodies
are produced against them.
• IgG blocks the binding of ACh
• Eventually destroys the receptor
• Causes diminished transmission of nerve
impulse across the NMJ and lack of muscle
depolarization
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• Cause is unknown.
Clinical manifestations
• Onset typically insidious
• May first appear during pregnancy, postpartum
or with the administration of certain anesthetic
agents
• Complaints are fatigue and progressive muscle
weakness
– Fatigue after exercise
– Recent history of recurrent upper respiratory
infections
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Clinical manifestations
• Muscles of the eyes, face, mouth, throat and
neck are usually affected first
– Levator and extraocular muscles affected most Diplopia, ptosis, and ocular palsies
– Muscles of facial expression, mastication,
swallowing and speech are the next most
involved
• Facial droop, expressionless face; difficulties in
chewing and swallowing, drooling, episodes of
choking and aspiration
• Nasal, low volume, high-pitched monotonous speech
pattern
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• Less frequently involved are the muscles
of the neck, shoulder girdle and hip flexors
– Fatigue requires periods of rest
– Weakness of arms and legs
– Difficulty maintaining head position
– Respiratory muscles of chest wall and
diaphragm become weak
• In advanced stage all muscles are weak
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Myasthenic crisis
• Severe weakness causes quadriparesis or
quadriplegia, respiratory insufficiency and
extreme difficulty in swallowing
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Cholinergic crisis
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Anticholinesterase drug toxicity
Intestinal motility increases
Fasciculation
Bradycardia
Pupillary constriction
Increased salivation
Increased sweating
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Evaluation
• Improvement with edrophonium chloride
(Telison) for several minutes
• EMG – amplitude of action potentials
declines
• Antiacetylcholine receptor antibody titers
• Antistriated muscle antibody titers
• MRI to rule out thymoma
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Progression
• Varies
• Appears first as a mild case that
spontaneously remits with a series of
relapses and symptom free intervals
• Over time can progress leading to death
• Ocular myasthenia has a good prognosis
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Treatment
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Anticholinesterase drugs
Steroids
Immunosuppressant drugs
Cyclophosphamide
Plasmapheresis during myasthenic crisis
Thymectomy is treatment of choice for
individuals with thymoma
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