Quantitative Analyses of Dynamic Strain Sensitivity in Human Skin Mechanoreceptors

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Abstract
Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64% · s−1, i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities >8% · s−1. Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains <0.5% and a typical SAII unit began to discharge at 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.