NCS-COMPOUND MUSCLE ACTION POTENTIALS (CMAP)

SUMMARY

1. CMAPs involve electrical stimulation of nerves and recording of the synchronized discharge of muscle fibers supplied by the nerve.

2. One records not from axons but from muscle fibers at a specified distance away from the stimulation.

3. Parameters: amplitude (baseline to peak), onset latency, CV (stimulate at two points along the nerve and take the difference in distance divided by the difference in latency).

4. CV: decreased by cold, advancing age, demyelination.

5. Amplitude: affected by number of axons, integrity of NMJ & muscle fibers. Reduction in amplitude can occur from any lesion distal to the anterior horn cell.

6. By 7 days after a proximal loss of motor cell bodies or axons, the distal response will disappear due to axonal degeneration.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].