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George E. Carvell, PhD, PT   University of Pittsburgh
PERIPHERAL NERVE CONDUCTION: Normal Sensory Nerve Conduction
  Antidromic Sensory Nerve Conduction Studies record responses from digital nerves or superficial cutaneous nerves. Stimuli are delivered at several locations along the course of the nerve. Brief (0.1 msec monophasic DC pulses at 1/sec) but strong (supramaximal strength) stimuli are used. Responses are recorded as simulated digital oscilloscope traces in these animations. A ground electrode is placed over non-contractile tissue (not shown). The example shown here is antidromic sensory nerve conduction for the Median Nerve. Ring recording electrodes are placed around the proximal and middle phalanges of the index finger. Proximal and distal stimuli & stimulation sites are the same as for median motor nerve conduction. Sensory compound action potentials are small (mV range) and high amplifier gain is required. If peripheral nerve disease is present the signal to noise ratio may require waveform averaging to reveal tiny responses buried within the background noise (note calibration scale on scope).
Unlike motor nerve conduction, sensory waveforms are small. Summation of all A myelinated sensory axons produces amplitudes in the 20-45 mV range (compared to ~ 10-15 mV for motor potentials). Normal distal latencies for the median nerve should be less than 3.5 msec and conduction velocity should be > 60 M/sec for adults. Actual normal values vary according to age. Distal & proximal stimulation site waveforms should have similar shape & area. However, waveform area due to proximal site stimulation is temporally dispersed compared to distal site (smaller amplitude, longer duration).
Normal Sensory Nerve Conduction
GMOMM  2001