Flashcards in Peripheral Nervous System Deck (30):
lose Schwann cells
affects one neuron
affects multiple neurons
multiple mononeuropathies (more rare)
two ways to test for neuromuscular disease
elctromyography - examine spontaneous and evoked electrical activity in skeletal muscle
nerve conduction velocity - measure velocity and amplitude of compound APs
What does a demyelinating neuropathy do to compound APs
If some axons are myelinated and some aren't, axons are still intact but since fewer axons have fast APs, the overall conduction velocity is reduced
(CONDUCTION VELOCITY REDUCED, AMPLITUDE DISPERSED)
What does an axonal neuropathy do to compound APs?
CONDUCTION VELOCITY NORMAL, AMPLITUDE REDUCED
since some of axons are gone, signal still travels at the same velocity, but there is less signal
What kinds of neuropathies are typically seen in axonal neuropathies?
Most toxic/metabolic neuropathies (ex: diabetes patients will often show polyneuropathies, alcohol poisoning)
What are two examples of diseases that are demyelinating neuropathies?
Guillan Barre syndrome (acquired, proteins turn on peripheral myelin which will transiently attack Schwann cells -> develops polyneuropathy)
Charcot Marie tooth disease - genetic, defected myelination
What nerve is "harmless" enough to do a high risk nerve biopsy on? (nerve biopsies tend to have high risk for nerve dysfunction)
the sural nerve (only for sensory neuropathies) (in the foot)
you don't want to do this on a useful nerve
onion bulb formation
Seen in demyelinating neuropathy (where are bunch of Schwann cells surround an axon and try to repeatedly remyelinate and demyelinate it ineffectively....cause nerve to dilate, almost palpable)
seen in Charcot Marie tooth disease
Two types of disorders affecting NMJ?
myastehnia gravis - autoimmune, thymic abnormalities, clear antibodies to treat
organophosphate intoxication - inhibit AchE, increase synaptic action of Ach, nerve gases, irreversible, very toxic (ex: sarin)
How to treat and dx myasthenia gravis?
treat - pyridostigmine (long acting reversible)
dx - edrophonium (very short acting)
Difference between type I and type II muscle fibers (histologically)
type I - dark red, oxidative
type II - light white, glycolytic
"RED, WHITE, BLUE"
fiber type is dependent on innervating neuron
What happens when muscle fibers lose their innervation?
They shrink/atrophy, then spread Ach all over diffusely (help me help me signal)
When a neuron dies, what do surrounding surviving neurons do?
A surviving neuron adopts the "orphaned/abandoned" fibers leading to type grouping
(de-innervation to re-innervation)
Usually, type I and type II fibers are scattered like a mosaic, but when fibers become de-innervated and subsequently re-innervated...they form clusters of of like type fibers. Good indicator of atrophy
What can indicate a progressive neurologic problem?
De-innervation, then re-innervation (type grouping), then de-innervation again (death of neuron that took up orphaned fibers)
How can you classify muscle biopsy findings?
1. neurogenic - type goruping, group atrophy, angular fibers, target fibers
2. myopathic - fiber size variability, basophilia, central nuclei, splitting, macrophages, fibrosis
Two types of myopathy?
degenerative - dystrophy
inflammatory - myositis
subsarcolemmal structural protein, located on X chromosome (disorders more common in males), X- linked recessive
Duchenne's dystrophy vs. Becker's
Duchenne's - severe, early onset, rapid progression
Becker's - milder, later onset, slower progression
all linked to dystrophin mutation!
difference in weakness in myopathies and neuropathies
myopathies - weakness proximally (trunk, limbs)
neuropathies - weakness distally
Characteristics of myotonic dystrophy
autosomal dominant, trinucleotide repeat amplification, myotonia (impaired muscle relaxation), distal wasting, balding, endocrine abnormalities
impaired muscle relaxation
Where are the nuclei seen in muscles with myotonic dystrophy?
INTERNAL NUCLEI, abnormal
2 types of inflammatory myopathy?
polymyositis - lymphocitic infiltration, muscle fiber destruction, PAIN and weakness, AUTOIMMUNE so treat with IMMUNOSUPPRESSION
inclusion body myositis - all the same except no pain while weak, not effective with immunosuppression, rimmed vacuoules
Classifications of myopathy?
dystrophy, inflammatory, congenital (structural protein disorders presenting in infancy or early childhood), metabolic, mitochondrial (genetic, maternally inherited, depends where bad mitochondria end up)