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86 Cards in this Set
- Front
- Back
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What are the 5 physioanatomic components of the peripheral nervous system?
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Anterior horn cell
Nerve root & Plexus Axon Neuromuscular Junction Muscle |
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Define trophism
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Movement
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Peripheral nerves have three layers of coverings. List them from outermost to innermost
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Epineurium (outermost)
Perineurium Endoneurium (innermost) |
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90% of peripheral nerves are...
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Small & Unmyelinated
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Anterograde axoplasmic transport is facilitated by what protein?
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Kinesin
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Retrograde axoplasmic transport is mediated by what protein?
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Dynein
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Name the two types of anterograde axoplasmic transport, their speed (mm/day), and what they transport.
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Fast (400 mm/day) - Vesicles, Enzymes, Neurotransmitter
Slow (1-2 mm/day) - Structural proteins |
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What is the speed of retrograde axoplasmic transport?
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100-200 mm/day
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What is Wallerian degeneration?
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Necrosis undergone by the distal portion of a transected nerve fiber
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What causes muscle atrophy?
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Denervation (disruption of neuromuscular junction)
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What occurs in denervated muscles?
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Fibrillation
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Describe the activation of a muscle fiber.
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1) Alpha motor neuron delivers action potential, releasing acetylcholine
2) Na/K+ channels depolarize 3) Calcium channels open, deliver calcium down T tubules 4) Ca binds receptors in sarcoplasmic reticulum (ryanodine receptors) 5) Activation of ryanodine receptors releases more Ca 6) Ca binds troponin, causing conformational change to displace tropomyosin 7) Myosin binds troponin - contraction can occur (requires ATP) |
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What symptoms can present from a lower motor neuron lesion?
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Weakness or flaccid paralysis
Gross Atrophy (denervation) Fibrillations Fasciculations Fiber-type grouping (reinnervation) Areflexia Single muscles can be affected Cranial motor nerves affected *Sensory intact |
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What are the types of Peripheral nerve disorders (5)?
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Mononeuropathy
Mononeuropathy multiplex Polyneuropathy Axonopathic Demyelinating |
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What is the cause of the neurodegenerative disorder, Amyotrophic Lateral Sclerosis (ALS)?
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Upper and lower motor neuron dysfunction
Some forms of the disease are hereditary |
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What is the clinical presentation of Amyotrophic Lateral Sclerosis?
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*No sensory loss
Paralysis of all skeletal mm except extra-oculars and sphincter mm Poor reflexes Fronto-temporal lobe dementia (40%) ~3 yr survival after onset |
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What is the state of the motor neurons at the time of diagnosis of Amyotrophic Lateral Sclerosis?
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~50% motor neurons are gone
*Delay is due to reinnervation compensation |
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What is the treatment for Amyotrophic Lateral Sclerosis?
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Riluzole - inhibits glutamate excitotoxicity
Physical therapy to maintain flexibility (not strength training, as this may hasten the disease) Good nutrition Non-Invasive Positive Pressure Ventilation (NIPPV) |
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What is Spinal Muscular Atrophy?
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Hereditary loss of survival motor neuron 1 (SMN-1) --> lower motor neuron disease of the Anterior Horn
Children are hypotonic, hyporeflexic, atrophied muscle, paresis Different phenotypes: Type I, II, III |
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What determines the severity of Spinal Muscular Atrophy and what are the phenotypes of the 3 types of SMA?
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Number of copies of survivor motor neuron 2 (SMN2)
Type I - 0-1 copy SMN2; death by 2yo Type II - 2-3 SMN2; wheelchair by 3-5yo Type III - 4-5 SMN2; can walk with paresis, until teen yrs |
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Name some Anterior horn cell disorders
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Amyotrophic Lateral Sclerosis (ALS)
Spinal muscular atrophy (SMA) Poliomyelitis Kennedy syndrome |
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What is Kennedy syndrome?
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X-linked spinobulbar atrophy caused by a defective androgen receptor
Pts present with proximal atrophy |
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How are motor, sensory, and sympathetic nerve fibers exiting via spinal roots organized?
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Organized by dermatome (sensory) or myotome (muscle)
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Name the major plexuses
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Cervical
Brachial Lumbar Lumbosacral |
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What clinical presentation will be observed when a root or plexus is lost?
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Dermatomal/Myotomal distribution of pain, weakness, sensory loss, and tendon reflex loss
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What is the term for damage or disease to a spinal root?
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Radiculopathy
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Provide some example radiculopathies
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Impingement from lateral herniation of nucleus pulposus
Diabetes (causes microinfarctions) Infarction Tumor Trauma |
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Describe the structure of an intervertebral disc
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Center = Nucleus Pulposus (gelatinous consistency), which is surrounded by the Annulus Fibrosus
Annulus Fibrosus is composed of lamellae |
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What is the term for damage or disease to the plexus
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Plexopathy
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Provide some examples of plexopathies
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Infection (plexitis)
Diabetes (microinfarctions) Trauma Tumor Radiation |
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What is it called when a single peripheral nerve is abnormal?
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Mononeuropathy
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What is mononeuropathy multiplex?
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Several separate peripheral nerves are abnormal
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What is polyneuropathy?
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All nerves are affected equally by a systematic process
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Provide an example of mononeuropathy
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Carpal Tunnel Syndrome (compression of median nerve)
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What is an axonopathic peripheral nerve disorder?
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Disorder interfering with axoplasmic transport; only recoverable via reinnervation
E.g. Cut axon --> distal atrophy, only recovered by reinnervation |
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What is a demyelinating peripheral nerve disorder?
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Axon loses its myelin
Remains intact, but saltatory conduction is interrupted NMJ maintained and functions when remyelinated |
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What is a conduction block?
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Failure of a demyelinated axon to perform saltatory conduct
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List the three classes of mononeuropathy
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Neuropraxia
Axonotomesis Neurotmesis |
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What is neuropraxia?
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Focal demyelination caused by entrapment (compression) neuropathy; saltatory conduction reduced
E.g. carpal tunnel syndrome |
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Is axonal structure disrupted in neuropraxia?
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No. Axon and NMJ intact. Only focal demyelination occurs & remyelinates in time
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What is axonotmesis?
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Axon disruption
Axonal injury results in Wallerian degeneration, but basement membrane is maintained & serves as channel from original axon to denervated muscle during regrowth |
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After axonal injury, what is the time course for Wallerian Degeneration?
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Axon below the lesion will completely degenerate over 3-8 days
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What is the rate of regrowth for peripheral axons?
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1 mm/day
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What is neurontmesis?
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Complete disruption of the axon.
Wallerian degeneration without maintenance of basement membrane. Therefore, muscle cannot be reinnervated (disorganized regrowth) |
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What is clinical presentation of mononeuropathies?
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Pain, weakness, sensory loss, loss of deep tendon reflexes in the distribution of the affected nerve(s)
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Provide some causes of mononeuropathies.
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Nerve compression (e.g. carpal tunnel syndrome)
Trama Infarction (diabetes, vasculitis) Lyme disease (facial n.) Amyloidosis (invading surrounding tissue) Fibular N. lesion --> weak tibialis anterior (foot drop) |
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What is amyloidosis?
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Abnormal deposition of amyloid proteins into tissues
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Provide some causes of mononeuropathy multiplex.
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Infarction (Diabetes, vasculitis)
Trauma Hereditary neuropathy with pressure palsies (cause neurotmesis) Amyloidosis (uncommon) |
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What is the clinical presentation of a polyneuropathy?
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Pain, weakness, sensory loss, deep tend reflex loss DISTALLY and SYMMETRICALLY
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List some causes of axonal polyneuropathy
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Infarction (Diabetes/Vasculitis)
Alcohol/Toxins Metabolic Uremia Infection Nutrition Hereditary |
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Name some causes and types of demyelinating polyneuropathy
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Inflammation
Hereditary Gammopathy Diptheria Types: Guillain-Barre syndrome Charco-Marie-Tooth Type I Chronic Inflammatory Polyneuropathy (CIDP) |
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Which is more common: axonal polyneuropathy or demyelinating polyneuropathy?
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Axonal
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How would a pt with Guillain-Barre syndrome present?
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Acute ascending paralysis
Areflexia Sensory loss Autonomic instability Requires respiratory and supportive care |
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What is the prognosis for Guillain-Barre syndrome?
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80-90% return to normal function within 6 months
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What causes Guillain-Barre syndrome and what is the proposed reason?
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Autoimmune attack on peripheral nerve myelin, possibly due to molecular mimicry of a virus/bacteria (epitope similar to that of peripheral myelin)
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What is the treatment for Guillain-Barre syndrome?
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Plasmapheresis, IVIg
*must be given within first 2 weeks of onset in order to decrease ventilator time/hospital stay |
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How is neurotransmitter released by the presynaptic cleft?
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Action potential reaches synaptic bouton, activating Ca channels
Initial influx of Ca causes assembly of synaptobrevin, SNAP-25, and syntaxin, which docks vesicle. Second influx of Ca activates synaptotagmin and triggers exocytosis & neurotransmitter release |
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What is a miniature endplate potential?
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The amount of electrical potential produced by one receptor
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What is an endplate potential?
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The summation of all the post-synaptic miniature endplate potentials
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Describe the three pools of vesicles in the synaptic bouton
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Main body - synaptic vesicles (SV) packaged with Ach; 100-1,000s SV
Mobilization stores - immediately available, but not yet lined up at active zones; ~100,000 SVs Immediately Available store - at active zone ~1,000 |
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Name two diseases of the neuromuscular junction.
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Myasthenia Gravis
Lambert-Eaton Syndrome |
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What is similar between Myasthenia Gravis and Lambert-Eaton Syndrome?
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Both are autoimmune disorders that target receptors involved in the neuromuscular junction and cause weakness.
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What is the difference between Myasthenia Gravis and Lambert-Eaton Syndrome?
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Myasthenia Gravis = post-synaptic Ach receptors bound by Ab; fatiguable weakness
Lambert-Eaton = pre-synaptic Ca channels bound by Ab; weakness improves with exercise |
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What is the clinical presentation of Myasthenia Gravis?
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Fatiguable weakness
Alternating ptosis and diplopia Any skeletal mm can be involved Thyomas (in some cases) |
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How is Myasthenia Gravis diagnosed?
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1) Administer edrophonium - short acting acetylcholinesterase-inhibitor --> Pt will be able to lift eyelids, move with more energy
*only lasts ~3 min 2) Antibody testing with anti-Acetylcholin receptor Abs (~70% cases) & anti-MuSK Abs (~10% cases) 3) Electrodiagnosis - electrical potentials duplicate natural mm contraction; observe to see if mm weakens |
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How is Myasthenia Gravis treated?
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Treatment is symptomatic --> Pyrostigmine (Mestinon), Neostigmine (AChE inhibitors)
Use corticosteroids for more severe disease (difficulty swallowing/breathing) Thymectomy to remove cells generating Abs targeting epitopes with Ach receptors |
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What is the clinical presentation of Lambert-Eaton Syndrome?
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Weakness that improves with exercise (more Ca released with more presynaptic depolarization, increased NT release)
When pts stop exercise, they feel weak again |
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What is the significance of dystrophin?
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Necessary for the stabilization of the muscle membrane during contraction
Loss of dystrophin results in Duchenne muscular dystrophy |
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What is the significance of the dystrophin-associated glycoprotein complex?
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Supportsdystrophin
Anchors muscle fiber to the extracellular matrix via merosin *Disruption of the complex results in a muscular dystrophy |
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Describe the Acetylcholine receptor (AchR)
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Needs 2 Ach molecules to bind in order to open channel
Na influx, K efflux |
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Describe the binding of botulinum toxin
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Irreversibly binds the SNARE proteins, preventing exocytosis
No treatment; Terminal axon must regrow Lethal Used in Botox |
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What is myopathy?
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Muscle damage or disease
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List some causes of myopathy
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Muscular dystrophy
Inflammation Channelopathies Congenital Endocrine Toxins Mitochondrial disease |
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What is the milder form of Duchenne muscular dystrophy?
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Becker Muscular Dystrophy
- x-linked - partial loss of dystrophin gene - muscle weakness - survival into late 20s, 30s |
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How does Duchenne Muscular Dystrophy present clinically?
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X-linked inheritance
Onset before age 5 Progressive proximal weakness until all muscles are affected Joint contracture Lordosis Scoliosis Cardiac, GI, and IQ deficits Waddling gait (weak gluteal mm --> pelvic falls) |
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How does the scoliosis experienced by children with Duchenne Muscular Dystrophy affect cardiac function? What is the treatment for this?
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Postural change causes compression on heart and lungs
By age 14, pts should have rod installed in back |
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How can the progression of Duchennes be pharmacologically slowed and what are the difficulties with this?
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Prednisone - Pts find the many side effects difficult to tolerate; many only stay on for a few years
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What is the average life expectancy of pt with Duchenne Muscular Dystrophy?
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10-12
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Which of the following muscular dystrophy's exhibits a founder effect:
Congenital Duchenne Limb-girdle Myotonic dystrophy Oculopharyngeal |
Oculopharyngeal
Founder effect for French Canadians and Spanish Americans (New Mexico) |
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Name three types of inflammatory myopathy
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Polymyositis
Dermatomyositis Inclusion Body Myositis |
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What is Polymyositis and how is it treated?
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Autoimmune disorder - targets muscle fibers causing inflammation, pain and weakness
Treatment: Immune suppression |
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What is dermatomyositis and what is its presentation?
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Autoimmune disease targeting mm blood supply (capillaries)
Causes skin effects: rash (dermatitis) around neck, chin, heliotrope rash (around eyes) |
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What is inclusion body myositis?
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Degenerative muscle disease characterized by progressive weakening, wasting, and inflammation of the muscle
*Note - this is not an autoimmune disease. Sometimes hereditary |
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What is the treatment for inclusion body myositis?
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No treatment. Slowly progressive
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What is the connection between Inclusion Body Myositis and Alzheimers Disease?
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Amyloid beta protein accumulates in both conditions
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What is the significance of mitochondria for muscle?
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Encodes 15 genes for the electron transport chain, which produces ATP
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