MORPHOLOGY OF ACTION-POTENTIALS RECORDED FROM HUMAN NERVES USING MICRONEUROGRAPHY

This study investigated the morphology of action potentials and the fr equency of occurrence of the various waveforms encountered when using microneurography to record single-unit muscle afferent activity in hum ans. With 75% of the afferents recorded in this study (55 of 73 affere nts), action potentials had a double-peaked morphology. For action pot entials with an initial, positive double-peaked morphology, the releva nt afferent conducts impulses past the microelectrode, with the second peak representing current fluctuations at the node of Ranvier proxima l to the electrode. Accordingly, in the majority of recordings, the af ferent is capable of conducting impulses to the spinal cord. The mean interpeak interval for these double-peaked units was 168 mu s (range 9 0-310 mu s). This represents marked prolongation of conduction time ac ross the impaled internode. When the interpeak interval was relatively short (90-120 mu s), the double-peaked morphology could be recognized only if the low-pass filter was high (greater than or equal to 10 kHz ). The probability of recording a double-peaked unit was the same whet her the recording was acquired early or late in a 3-h experiment. Cond uction block developed in 6 of 73 single units during the recordings. These findings indicate that the majority of isolated single afferents and, indeed, the majority of afferents within the relevant fascicle a re capable of transmitting impulses across the recording site, even th ough conduction across the impaled internode is slow.