SNCV Flashcards
Name the three levels of stimulus
- 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.
Describe CNSAP waveforms
- 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
3 reasons why SNCV is ____(slower vs faster) with distal stimulation (tibial nerve)
Slower, due to:
1. Lower distal T°
2. Smaller myelin diameter
3. smaller internodal distance
Most commonly studied nerves
Radial, ulnar (brachial plexus)
Peroneal/fibular, tibial (sciatic)
Saphenous (femoral)
lateral superficial radial, Superficial peroneal,
Rough, normal range of SNCV in dogs vs cats?
dogs: 50-65 m/s
cats: 65-85 m/s
Understand electrode montage
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
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) dorsolateral TL
b) ventromedial TL
c) Medial aspect of the PL
d) dorsolateral TL (the fibular is lateral!)
e) ventromedial TL
Which SNCV abnormalities are expected? what do they mean? (similar to MNCV)
- ↑ latency = demyelination
- ↓ amplitude = axonopathy (neuropraxia or axonotmesis) with remaining fuctional axons
- Absent potential = axonopathy (neuropraxia, axonotmesis or neurotmesis)
Slide 39
Scan thru slide 40
With equine idiopathic head shaker syndrome, what SNCV alteration is expected?
Trigemilal hyperexcitability =
Lower threshold stimulus for infraorbital and maxillary nerves (CNV branches)