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85 Cards in this Set
- Front
- Back
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What is a Motor Unit?
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A lower motor neuron plus the myofibers that it innervates
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How many muscle fibers are innervated by the oculomotor nerve? The gastroc?
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Oculomotor - a few
Gastrocnemius - hundreds |
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How are the muscle fibers innervated by the same nerve spread throughout a muscle?
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In a checkerboard fashion - not all together.
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What are the 4 broad classifications of diseases of the motor unit?
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1. Motor neuron diseases
2. Peripheral nerve diseases 3. NMJ diseases 4. Muscle diseases |
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What are 2 diseases of motor neurons that affect motor units?
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-Amyotrophic lateral sclerosis
-Progressive muscular atrophy |
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What kind of diseases are ALS and progressive musc atrophy? What is their etiology?
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Degenerative diseases of unknown etiology.
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What chemical agents can cause diseases of motor neurons?
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-Adriamycin
-Vincristine -Aluminium |
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What part of the motor unit is primarily affected in diseases of motor neurons?
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The Cell Body (perikaryon)
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What are some changes that an affected neuron will show in diseases of motor neurons?
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-Loss of Microtubules
-Nuclear displacement -Increased cytoplasmic neurofilaments -Tangling of neurofilaments |
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What agent is associated with causing increased cytoplasmic neurofilaments?
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Adriamycin
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What agent is associated with causing tangling of neurofilaments?
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Aluminium
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Why do diseases of motor neurons cause muscle dysfunction?
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Because when a perikaryon degenerates, the axon does too.
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What virus tends to affect motor neurons?
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Poliomyelitis
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What virus tends to affect sensory neurons?
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-Herpes
-VZV |
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How areneuromuscular diseases of Peripheral nerves classified?
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According to Pathology
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What are 3 pathological classes of Peripheral Nerve neuromuscular diseases?
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-Axonal degeneration/neuropathy
-Schwann cell disorders/dmylntv -Mixed Axonal/Demyelinative neuropathy |
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What are 2 subcategories of axonal neuropathy?
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-Wallerian degeneration
-Axonal degeneration caused by other diseases |
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What is the main cause of pathological changes in axon degeneration?
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Decrease or loss of axoplasm
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What is Wallerian degeneration?
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Axon transection due to crushing or cutting
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In what direction does the axon degenerate when due to Wallerian degeneration?
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Distal to the transection, going from proximal to more distal.
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What happens to the stumps of a transected axon within 1-2 hrs?
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They retract
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What happens to the axon stumps?
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They swell with degenerate cytoplasmic organelles, then undergo fragmentation and shrink.
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What happens to myelin in Wallerian degeneration?
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It also undergoes degeneration and forms globules within the Schwann cell cytoplasm.
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What are globules that contain mainly myelin called?
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Myelin ovoids
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What are globules that contain mainly axonal materials called?
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Axonal ovoids.
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What cells respond to myelin degeneration?
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Macrophages
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What change is seen 2-4 days after wallerian degeneration?
-In neuronal cell body -In the proximal axon stump |
Perikaryon - Central chromatolysis
Prox axon stump - axonal swelling |
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What does the neuron cell body do during axonal regeneration after wallerian degeneration?
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It remains in a highly active metabolic state.
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How soon after a nerve transection does regenerative activity become evident?
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Within a few hours
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How does nerve regeneration proceed?
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Axonal sprouts grow from proximal stumps to the vacated originatl paths of severed axons where Schwann cells accumulate
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What is the average rate of growth of regenerating axons?
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2-5 mm/day
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What will form if fibrosis or inflammation prevent the axon from reaching its end organ?
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A traumatic neuroma - excessive axonal sprouts/growth along with fibrous tissue
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How are regenerated axons different from original? (5 ways)
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-Increased # of internodes
-Decreased internode length -Decreased axon diameter -Decreased myelin lamellae -Increased endoneural collagen |
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What are 3 ways that axon degeneration caused by other diseases differs from Wallerian axon degeneration?
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1. Less axoplasm leak
2. Longer time period (chronic) 3. Decreased inflammatory response |
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What is the most likely mechanism by which Diseases cause axonal degeneration?
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By changes in the neuron cell body which decrease axoplasm synthesis
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How do most neuropathies which affect peripheral nerves cause axon degeneration?
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By affecting the axons.
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What are 2 subdivisions of axon degeneration caused by disease?
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1. Proximal axon degeneration
2. Distal axon degeneration |
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How does Proximal axon degeneration occur?
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A focal blockage of the axon prevents materials from being transported to distal parts of the axon
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What resulting change is seen in the distal axon due to Proximal axon degeneration?
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It shrinks
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How do the majority of disease induced axon degenerations occur?
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By Distal axonal degeneration
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What is Distal axonal degeneration also called?
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Dying back neuropathy
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What is Dying Back?
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Pattern of peripheral nerve fiber degeneration where earliest changes occur in the most distal axon portions, then spread proximally.
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What is Dying back neuropathy caused by?
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Degeneration of neurons
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What is the cause of many diseases with distal axonal degeneration?
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Hereditary
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What are some acquired causes of distal axonal degeneration?
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Drugs, lead, metabolic diseases, and others.
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What is another name for Schwann cell disorders or neuromuscular function?
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Demyelinative neuropathy
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What is the pattern of demyelination in Schwann cell disorders?
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Segmental, affecting internodes in a random manner.
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What effect does demyelination have on nerve impulse conduction?
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IT slows the rate of conduction
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What are 2 subclasses of demyelinative neuropathies?
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1. Primary demyelination
2. Inflammatory demyelination |
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What is Primary demyelination due to?
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Interference with Schwann cell metabolism
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What are 4 disorders associated with Primary demyelination and schwann cell dysmetabolism?
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-Diphtheria
-Rheumatoid arthritis -Ischemia -Leprosy |
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What is the prototype example of Inflammatory demyelination?
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Guillain barre syndrome
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What is another name for Guillain barre?
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Acute inflammatory demyelinating polyradiculoneuropathy
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What type of inflammation occurs in Guillain barre?
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Perivascular endoneurial mononuclear infiltration
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How do the mononuclear phagocytes cause peripheral nerve damage in Guillain barre?
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By penetrating the schwann cell basement membrane and displacing its cytoplasm.
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What is the result of phagocytic displacement of Schwann cell cytoplasms?
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Myelin is stripped away and digested.
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Where is the most severe damage usually seen in Guillain barre?
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In the proximal part of nerve roots
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Where does the weakness start out in Guillain barre?
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In distal extremities
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What is thought to be the cause of Guillain barre?
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Viral infections, Campylobacter jejuni infections, or Mycoplasma induced antibody against nerves.
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What are the predominant symptoms of guillain barre?
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Motor nerve symptoms
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How does Guillain barre progress in most cases?
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Rapidly to total paralysis of extremities and respiratory muscles.
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What is the outcome of Guillain barre in most cases?
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Complete or almost complete recovery
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If axons actually demyelinate in advanced stages of G. barre, how does axon regeneration compare to that in demyelinative disorders?
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More slowly
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What is the most common type of neuropathy?
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Mixed - both axonal damage and demyelinative, with one generally predominant.
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What is the most common form of genetic neuropathy that shows a mixed pathology?
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Charcot-Marie-Tooth disease
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What are the 4 hallmark features of Charcot-marie-tooth?
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-Progressive leg muscle atrophy
-Foot drop -Deformed feet -Less severe sensory changes |
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What morphology is often seen in nerve biopsies from Charcot-marie-tooth patients?
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Onion bulb formation of regenerative Schwann cells around axons.
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What type of nerve fibers are affected in most neuropathies?
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Both motor/sensory, but one predominantly.
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What type of nerve fiber is more predominantly affected by Lead poisoning?
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Motor
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What type of nerve fiber is more predominantly affected by Arsenic poisoning?
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Sensory
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What are the 3 diseases of the neuromuscular junction?
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1. Myasthenia gravis
2. Myasthenic Syndrome 3. Botulism |
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What is another name for Myasthenic syndrome?
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Eaton-Lambert
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What is Myasthenia gravis?
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An autoimmune disease of the NMJ
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What are the clinical features of M. gravis?
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-Fatigue
-Weakness -Mainly affecting oculomotor nucleus |
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How does activity affect M. gravis weakness?
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It increases weakness, so patients are strongest in the morning and weakest at night.
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What is the antibody directed against in M. gravis?
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The nicotinic ACh receptor on muscles
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Where are the antibodies against the ACh receptor produced?
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By B cells in the thymus
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So what conditions are associated with higher incidence of M. gravis?
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-Thymoma
-Thymic hyperplasia |
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What is needed to overcome the ACh receptor block in M. gravis?
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Activity by the patient to increase the ACh in the synapse
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What decreases degradation of ACh?
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ACh-esterase inhibitors - Neostigmine/Physostigmine
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What are 2 conditions in which patients can have Myasthenic syndrome?
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-Small cell carcinoma of lung
-Autoimmune diseases |
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What do the antibodies in Myasthenic syndrome attack?
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-Release sites of ACh
-Calcium channels needed to stimulate ACh release |
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So when are patients with M. syndrome most strong/weak?
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Strongest = at night
Weakest = in morning |
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How does exercise affect strength in patients with M. syndrome?
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It increases their strength by increasing calcium uptake.
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How does Botulism cause NMJ disease?
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It inhibits the release of ACh at the presynaptic terminal resulting in flaccid paralysis.
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