SNCV Flashcards

1
Q

Name the three levels of stimulus

A
  • Threshold: minimal stimulus required to elicit a repose. Stimulates a fraction of the nerve fibers.
  • Maximal: stimulates all nerve fibers
  • Supraaximal: 8x threshold. Interference from muscle potentials.
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2
Q

Describe CNSAP waveforms

A
  • Smaller amplitude and poorer signal-to-noise ratio than CMAPs
  • Shock (stimulus) artifact -> initial positive (downward) deflection followed by large negative (upward) deflection
  • Amplitude = peak-peak
  • Latency = stimulus artifact -> onset of negative deflection

slide 17

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3
Q

3 reasons why SNCV is ____(slower vs faster) with distal stimulation (tibial nerve)

A

Slower, due to:
1. Lower distal T°
2. Smaller myelin diameter
3. smaller internodal distance

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4
Q

Most commonly studied nerves

A

Radial, ulnar (brachial plexus)

Peroneal/fibular, tibial (sciatic)

Saphenous (femoral)

lateral superficial radial, Superficial peroneal,

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5
Q

Rough, normal range of SNCV in dogs vs cats?

A

dogs: 50-65 m/s
cats: 65-85 m/s

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6
Q

Understand electrode montage

A

Basically opposite as MNCV since electrical impulses flow in the opposite direction.

1 set of stimulating electrodes (cathode + anode) distally, on the dermatome of interest

2 sets of recording electrodes (active + reference)

1 ground between stimulating and recording electodes

Slide 27-28

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7
Q

Know where each nerve is stimulated (dermatomes):
a) Superficial lateral radial nerve
b) Ulnar nerve
c) Saphenous nerve
d) Peroneal (fibular) nerve
e) Tibial nerve

where to place the stimulating electrode

A

a) dorsolateral TL
b) ventromedial TL
c) Medial aspect of the PL
d) dorsolateral TL (the fibular is lateral!)
e) ventromedial TL

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8
Q

Which SNCV abnormalities are expected? what do they mean? (similar to MNCV)

A
  • ↑ latency = demyelination
  • ↓ amplitude = axonopathy (neuropraxia or axonotmesis) with remaining fuctional axons
  • Absent potential = axonopathy (neuropraxia, axonotmesis or neurotmesis)

Slide 39

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9
Q

Scan thru slide 40

A
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10
Q

With equine idiopathic head shaker syndrome, what SNCV alteration is expected?

A

Trigemilal hyperexcitability =

Lower threshold stimulus for infraorbital and maxillary nerves (CNV branches)

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