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123 Cards in this Set
- Front
- Back
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Define orthodromic |
when impulse travels the same way it would physiologically
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Define antidromic
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when impulse travels opposite the way it would physiologically
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4 major uses for electrodiagnostics (reasons to order)
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1. diagnosis
2. localization 3. help determine treatment 4. prognosis |
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3 major types of EMG needles
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1. monopolar
2. bipolar 3. concentric |
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Role of filters (most generally)
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faithfully reproduce the signal you want while trying to exclude both high and low frequency electrical noise
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As sensitivity is increased, onset latency
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decreases
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Typical conduction velocity in a myelinated nerve
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40-70 m/sec
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Typical conduction velocity in an unmyelinated nerve
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1-5 m/sec
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Conduction block = neur____
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neurapraxia
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Conduction slowing and conduction block are indicative of
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demyelination
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Normal conduction velocity in upper extremity (general)
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50 m/sec
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Normal conduction velocity in lower extremity (general)
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40 m/sec
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CMAP amplitude is dependent on these 3 general factors
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1. integrity of the axons
2. muscle fibers depolarized by axons 3. conduction velocity of individual fibers |
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Motor nerve amplitudes are measured in
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microvolts
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Sensory nerve amplitudes are measured in
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millivolts
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Is temporal dispersion seen in congenital neuropathies?
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not usually
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True or false, in general the cathode is placed towards the direction of stimulation?
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true
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Optimal separation distance for active and reference electrodes in SNAPs
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3-4cm
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General placement of the ground electrode
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between the stimulation and the recording electrode
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In H-reflex we use _____maximal stimulation
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sub
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What happens to the H-reflex with supramaximal stimulation
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it dissapears (replaced by M-wave)
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H-reflexes in S1 are often absent in normal individuals over the age of ___
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60
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Formula for the f-wave ratio
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(F-wave latency - CMAP latency) - 1ms/(CMAP latency x2)
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Normal F-wave ratio in upper limb
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1.0 +/- 0.3
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Normal F-wave ratio in lower limb
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1.1 +/- 0.3
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An f-wave ratio higher than 1.3 indicates
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a proximal lesion
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An f-wave ratio lower than 0.7 indicates
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a distal lesion
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For motor studies, normal stimulation site differences for amplitude may be around ___
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20%
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How can you verify that a low amplitude is from segmental demylination and resultant temporal dispersion?
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the area under the curve should be unchanged
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Skin measurements appear to be accurate to about what factor?
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1cm
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How can you estimate the % of axonal motor loss?
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Compare the amplitude to the other side
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When stimulating the ulnar nerve, the elbow should be
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flexed 70-90 degrees
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Type of synapse in the H-reflex
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monosynaptic (or oligosynaptic)
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Type of synapse in the F-wave
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polysynaptic
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Sensory and motor pathway directions in H-reflex
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Sensory orthodromic
Motor antidromic |
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Sensory and motor pathway directions in F-wave
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Motor antidromic
Motor rothodromic |
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Stimulus required in H-reflex
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submaximal
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Stimulus required in F-wave
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supramaximal
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Where can the H-reflex be normally elicited?
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soleus
flexor carpi radialis |
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Where can the F-wave be normally elicited?
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most muscles (distal preferred)
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Where is the stimulus cathode places for the H-reflex?
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proximal
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Where is the stimulus cathode places for the f-wave?
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proximal
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What is the size of the H-reflex compared to the m-wave?
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large
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What is the size of the F-wave compared to the m-wave?
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small
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What facilitates the H-reflex?
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* anything that increases motor-neuron pool excitability (contraction, CNS lesion)
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What facilitates the f-wave?
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facilitation does not apply here
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Two major uses of the H-reflex
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S1 radiculopathy
Guillain-Barre' |
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3 major uses of the F-wave
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Demyelinating polyneuropathies
Guillain-Barre' Proximal nerve/root injury |
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Reproducibility of the H-reflex
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latency and configuration reproducible, amplitude varies depending on stimulation
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Reproducibility of the F-wave
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variable in amplitude, latency and configuration
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What's the general guide for upper limit of ok side-to-side difference for H-reflex?
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>1.5msec
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What's the general guide for upper limit of ok side-to-side difference for f-wave in hand, calf and foot?
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hand: >2 msec
calf: >3 msec foot: > 4 msec |
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What do F-wave ratios assume for distance?
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That the distance of stimulation is halfway between distal site and spinal cord (elbow or knee)
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Overall muscle contraction is from _____fusal fibers
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extrafusal
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Intracellular resting potential of extrafusal fibers
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-80mV
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Fundamental structure assessed during EMG
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the motor unit
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What makes up a motor unit?
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Anterior horn cell; axon; all muscle fibers that that axon innervates
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Motor unit architecture refers to its:
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size, distribution and endplate area
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Which type of motor units fire first?
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Type I, smallest
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In EMG the needle is the ____ electrode
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active
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The reference for EMG should be placed
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over the muscle being tested
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The ground for EMG can be placed
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anywhere on the extremity being tested
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A monopolar needle records the voltage differences between
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the needle tip and the reference electrode
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Which registers a larger potential - a monopolar or concentric needle?
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monopolar
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A monopolar needle electrode picks up from a ____ degree field
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360
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A concentric needle electrode picks up from a ____ degree field
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180
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Which registers more polyphasicity- a monopolar or concentric needle?
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monopolar
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4 parts to the EMG
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1. insertional activity
2. muscle at rest 3. analyze motor unit 4. recruitment |
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Basic filter and amplifier settings to check prior to starting EMG
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- low freq filter 10-30 Hz
- high filter 10,000-20,000 Hz - amplifier sensitivity 50-100 microvolts per division - sweep 10ms per division |
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Inserting a needle into atrophied muscle often feels like inserting the needle into
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sand
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Insertional activity that lasts longer than ____ ms is considered increased
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300
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List 4 examples of spontaneous activity generated by muscle
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- fibrillation potentials
- positive sharp wave - myotonic discharges - complex repetitive discharges |
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List 6 examples of spontaneous activity generated by nerve
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- myokymic discharges
- cramps - neuromyotonic discharges - tremors - multiples - fasciluations (may be mm or nerve) |
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Gain on EMG for looking at sponateous activity often needs to be set at
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50-100microvolts
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7 examples of chronic muscle disorders associated with positive sharp waves and fibrillation potentials
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- inflammatory myopathies
- muscular dystrophies - inclusion body myositis - cogenital myopathies - rhabdomyolysis - muscle trauma - trichinosis |
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6 examples of neurogenic disorders associate with positive sharp waves and fibrillation potentials
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- radiculopathy
- axonal peripheral neuropathy - plexopathies - entrapment neuropathies - motor neuron disease - mononeuropathies |
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5 examples of chronic muscle disorders associated with complex repetitive discharges
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- myopathies
- inflammatory processes - limb-girdle dystrophy - myxedema - Schwartz-Jampel syndrome |
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5 examples of neurogenic disorders associated with complex repetitive discharges
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- chronic myopathy or radiculopathy
- poliomyelitis - spinal muscular atrophy - motor neuron disease - hereditary neuropathies |
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Complex repetitive discharges are suggestive that the lesion is more than ____ old.
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6 months
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Clinical correlation of myotonic discharges on EMG
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delayed muscle relaxation after a forceful contraction
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7 examples of disorders associated with myotonic discharges
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- myotonic dystrophy
- myotonia congenita - paramyotonia - hyperkalemic periodic paralysis - polymyositis - acid maltase deficiency - chronic radiculopathy/neuropathy |
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5 examples of disorders associated with myokymic discharges
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Facial muscles:
- Bell's palsy - multiple sclerosis - polyradiculopathy Limbs: - chronic nerve lesions - radiation plexopathy |
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3 things that tell you you are likely in the endplate region
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1. Miniature endplate potentials
2. Endplate spikes 3. Pain |
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MEPPs represent
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spontaneous release of Ach from the presynaptic terminal and the resultant local depolarization
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Endplate spikes represent
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single muscle fiber depolarizations
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What do positive waves mean when they are found in the endplate?
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They are likely a normal finding and interpretation otherwise is not wise
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What should you do if you find yourself in the endplate?
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Get out; either by withdrawing needle or advancing firmly
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Typical sweep speed and gain during minimal contraction during EMG?
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sweep 10msec/div
gain 200-500 microvolts |
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4 parameters to evaluate the components of motor unit action potential morphology
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1. amplitude
2. rise time 3. duration 4. phases |
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MUAP amplitude is measured from
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most positive to most negative peak
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Acceptable rise time on MUAP is ___msec or less
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0.5
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Duration is measured as
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the initial departure from baseline to the return to baseline
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Normal MUAP duration (general)
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5-15 msec
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Why is MUAP duration often decreased in myopathies?
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Because there are fewer muscle fibers available to contribute to the MUAP.
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2 major ways of counting phases:
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1. the number of times it crosses the basline
2. the peaks and valleys across baseline +1 |
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Which is a better measure of pathology, motor unit duration or polyphasicity?
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duration
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Name the two ways that a muscle contraction can become stronger
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1. the same motor unit fires faster
2. additional motor units fire |
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The INITIAL motor unit firing (patient just thinking about moving the muscle) is often
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2-3 Hz and irregular; switches to regular when at 5 Hz
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How do you find the recruitment ratio?
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Hz of fastest motor unit divided by the number of motor units
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MUAP recruitment ratio above 8 suggests
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neuropathic process
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MUAP recruitment ratio less than 3 suggests a
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myopathic process
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Why is it difficult to evaluate type II motor fibers on EMG?
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By the time type II fibers are recruited the baseline is obscured by the activity of type I fibers
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Why might EMG be normal in a patient with a steroid myopathy?
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Steroid myopathy typically involves type II fibers which are not easily studied on EMG
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What are the three types of nerve injury in the Seddon classification of nerve injuries?
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- neurapraxia
- axonotmesis - neurotmesis |
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What is neurapraxia?
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Damage to the myelin
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Damage to myelin is called
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neurapraxia
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What is axonotmesis
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injury only affecting the nerve's axons
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An injury only affecting the nerve's axons is called
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axonotmesis
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What is neurotmesis?
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injury affects the myelin, axons and all supporting structures
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injury that affects the myelin, axons and all supporting structures is labeled
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neurotmesis
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Name the 4 general categories of demyelinating injuries
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1. uniform demyelination
2. segmental demyelination 3. focal nerve slowing 4. conduction block |
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Where is uniform demyelination typically seen?
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in hereditary disorders such as Charcot-Marie-Tooth disease
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Clinically, conduction block should present as
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weakness
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In a pure neurapraxia, EMG testing will be
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normal (unless conduction block is present)
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What would EMG show if there is conduction block?
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decreased recruitment
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How fast do peripheral nerve axons regrow?
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1mm/day, 1 inch per month
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Effect of cold temp on latency
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prolonged (0.2 ms/degree C)
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Effect of cold on amplitude
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increased (sensory more than motor)
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Effect of cold on conduction velocity
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decreased (1.8-2.4 m/s/degree C)
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Effect of cold on duration
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increased
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Repetitive nerve stimulation in a patient with NMJ disease is likely to be _____ if they are cold
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normal
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General temperature goals in NCS
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- upper limb: above 32C
- lower limb: above 30C |
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Positive initial deflection in CMAP with median nerve stimulation at the wrist should prompt consideration of
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Martin-Gruber Anastomosis
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