CHAPTER 72 Somatosensory-Evoked Potentials and Spinal Surgery
5 At what points along the neurosensory pathway are somatosensory-evoked potentials most commonly recorded?
6 Describe the characteristics of the somatosensory-evoked potential waveform
The SSEP is plotted as a waveform of voltage vs. time. It is characterized by:
Latency (L), which is the time, measured in milliseconds, from onset of stimulus to occurrence of a peak or the time from one peak to another
Morphology, which is the overall shape of the waveform, described as positive (P, below the baseline) or negative (N, above the baseline)
A waveform is identified by the letter describing its deflection above or below the baseline followed by a number indicating its latency (e.g., N20) (Figure 72-1).
7 Name several characteristic peaks important for the evaluation of somatosensory-evoked potentials
See Tables 72-1 and 72-2.
Peak | Generator |
---|---|
N9 | Brachial plexus (Erb’s point) |
N11 | Dorsal root entry zone (cervical spine) |
N13, 14 | Posterior column (nucleus cuneatus) |
P14 | Medial lemniscus |
N20 | Somatosensory cortex |
Peak | Generator |
---|---|
N20 | Dorsal root entry zone (lumbar spine) |
N40 | Somatosensory cortex |