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40 Cards in this Set
- Front
- Back
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What comprises a motor unit in the peripheral nervous system?
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Anterior Horn Soma
Axon All muscle fibers it innervates |
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List the connective tissue sheaths surrounding peripheral nerves. Begin with innermost sheath.
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Endoneurium (encloses myelin sheath)
Perineurium (encloses fascicles) Epineurium (outermost layer; surrounds peripheral nerve) |
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What is the main skeletal protein of nerve fibers? What is its relation with axon size?
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Neurofilaments
More neurofilaments-->bigger axons-->increased speed of propagation |
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What is Wallerian degeneration?
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When part of axon is blocked/removed from cell body and degenerates
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What are the consequences of deinnervation of muscle?
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Without neuron, muscle no longer received trophic factors and atrophies. Results in fibrillations (only detectable on EMG)
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Briefly describe the molecular events of muscle contraction.
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Sarcoplasmic Reticulum releases Ca2+
Ca2+ binds myosin (thick) Myosin binds troponin Troponin changes conformtn Tropomyosin moves off actin binding site Myosin binds actin BS REQUIRES ATP FOR CONTRACTION AND RELAXATION |
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How do Type I muscle fibers differ from Type II muscle fibers?
How would tell the two apart via microscopy? What determines muscle type? |
Type I: Oxidative, slow firing, fatigue-resistant
Type II: Anaerobic, glycolytic, fast firing, fatigue easily Type I is lighter on slides Type II is darker on slides Innervating neuron determines muscle type. |
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What are clinical signs of anterior horn cell damage?
Are cranial nerves affected? |
Doesn't involve nerve fibers, only involve soma in anterior horn
Expect diffuse muscle weakness, diffuse deep tendon reflexes, NORMAL sensation Motor cranial nerves affected (Recovery depends on other intact motor units reinnervating effected fibers) |
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How could you tell if an area of muscle fibers had been re-innervated?
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On slide, muscle types would appear grouped in clusters
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Provide examples of anterior horn cell disorders.
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Amyotrophic lateral sclerosis (ALS; Lou Gherig's)
Spinal muscular atrophy (SAR) Polio Kennedy Syndrome |
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How does SMA Type 1 differ from SMA Type 2?
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SMA Type 1: Survival Motor Neuron Gene 1 product is not produced, SMNG 2 product is not produced
SMA Type 2: No SMNG 1, but have 2 or 3 SMNG 2 genes (milder version of dz) (SMNG2 product is similar that of SMNG1, but it has a shorter half-life due to failure to transcribe exon 7) |
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Nipple line dermatome.
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T4
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When an enlisted person receives an order that conflicts with a previously received order, which of the following actions should that person take?
1. Obey the first Order 2. Obey the last order 3. Obey neither order 4. Obey both orders |
Obey Last order
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What are clinical signs of root/plexus damage?
Are cranial nerves affected? |
Damage shows effect (muscle weakness, deep tendon reflex, sensory) limited to 1 region
Cranial nerves are NORMAL |
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What are causes of root/plexus damage?
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Degenerative spine dz
Trauma Imunnologic: plexitis Neoplastic: invasion, compression, meningeal DM |
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Myelinating Disease vs Axonopathic Diseases
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Myelinating: affects myelinated axons (usually those of vibratory sensation and reflex arc)
Axonopathic: affect axon; usually interfere with axonal transport |
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What is the effect of a demyelinating disease on neuromuscular junctions?
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None. NMJ is maintained (still have release of trophic factors); however there is conduction block because of interrupted saltatory conduction.
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What is required for Wallerian Degeneration?
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Complete separation of a portion of the axon from the soma.
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What is neuropraxia? Give an example.
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Class 1 mononeuropathy
No disruption of axon, maintains NM Junction (best prognosis) Ex: Carpal Tunnel |
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What is axonotmesis?
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Class 2 mononeuropathy
Wallerian degeneration; Basement membrane of Schwann cells is maintained; When nerve regrows can re-innervate muscle fibers |
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What is neurotmesis?
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Class 3 Mononeuropathy: axon AND basement membrane of Schwann cell interrupted; get Wallerian degeneration, deinnervation, nerve cannot reinnervate; form naked nerve endings (neuromas)
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What are clinical signs of a fibular nerve neuropathy?
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Loss of sensation around lateral leg, dorsum of foot.
Also get FOOT DROP. Remember: mononeuropathies are regional. |
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What are causes of mononeuropathy?
Causes of mononeuropathy multiplex? |
Causes of mononeuropathy:
Compression (carpal tunnel) Trauma Infarction, DM Invasion Lyme Dz Multiplex: DM Vasculitis Trauma Genetic Amyloidosis (invasion) |
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What are clinical signs of nerve fiber damage?
Are cranial nerves affected? |
Problems (sensory, deep tendon reflex, and motor) begin distally (feet) and ascend from there
Cranial Nerves may be affected if SEVERE |
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What are the two categories of polyneuropathy?
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Axonal
Demyelinating |
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What is Guillain-Barre Syndrome?
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Demyelinating polyneuropathy
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What proteins are required for the binding of synaptic vesicles?
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SNAP-25
Synaptobrevin Syntaxin |
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Impetigo
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contagios skin infections characterized by blisters that later erupt to form yellowish crust
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What is the neuromuscular junction safety factor?
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End plate potential is always in excess of depolarization required to reach threshold
When safety factor drops below threshold, get muscle weakness (only occurs in disease processes) |
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What are clinical signs of neuromuscular junction damage?
Are cranial nerves affected? |
Diffuse motor/reflex weakness, normal sensation
Motor CN's affected |
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Provide an example of a neuromuscular junction disease.
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Myasthenia gravis (autoimmune attack on ACh receptors, decreased ACh receptors, decreased safety factorl muscle weakness)
Postsynaptic dz! |
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What are the hallmarks of myasthenia gravis?
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Rapid fatigue of muscles
Bilateral ptosis Facial weakness |
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Provide two examples of pre-synaptic diseases.
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1) Lambert Eaton Myasthenic Syndrome: Ab attack against Ca2+ channels (improves w/exercise)
2) Botulism: toxin irreverisbly binds SNAP-25, synaptobrevin, synapsin; can no longer bind syn vesicles. Axon terminal must regrow. |
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What are clinical signs of muscle damage?
Are cranial nerves affected? |
weakness in sterngth/deep tendon reflexes of PROXIMAL muscles (chest/shoulder, hip muscles), no sensory abnormalities
Normal CNs |
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Provide examples of myopathies.
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Duchenne muscular dystrophy
Limb-girdle MD Congenital MD Oculopharyngeal MD etc. |
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What are the clinical signs of Duchenne MD?
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Progressive proximal weakness
Calf hypertrophy Scoliosis, joint contractures |
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What would you expect to see in a normal dystrophin stain? Abnormal?
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Normal: dystrophin should be distributed along sarcolemma
Abnormal: no dystrophin |
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Provide an example of an inflammatory myopathy.
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Dermatomyositis (autoimmune attack against capillaries of muscle fibers)
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What is the muscle equivalent of Alzheimer's disease?
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Inclusion body myopathy (involves Amyloid-beta 42 protein)
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Are mitochondrial myopathies limited to muscle?
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No, all cells affected
(maternal inheritance) |
