SNCV

Question 1

Name the three levels of stimulus

Answer 1

• 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.

Question 2

Describe CNSAP waveforms

Answer 2

• 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

Question 3

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

Answer 3

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

Question 4

Most commonly studied nerves

Answer 4

Radial, ulnar (brachial plexus)

Peroneal/fibular, tibial (sciatic)

Saphenous (femoral)

lateral superficial radial, Superficial peroneal,

Question 5

Rough, normal range of SNCV in dogs vs cats?

Answer 5

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

Question 6

Understand electrode montage

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Slide 39

Question 9

Scan thru slide 40

Question 10

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

Answer 10

Trigemilal hyperexcitability =

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