Single unit analysis of mechanoreceptor activity from the human glabrous skin.

Single unit impulses were recorded from the median and the ulnar nerves in waking human subjects with percutaneously inserted tungsten electrodes. 61 mechanoreceptor units in the glabrous skin were analysed with regard to the characteristics of their receptive fields and the basic physiological properties of their endings. 4 different types of receptors could be distinguished. This distinction was based mainly upon the adaptation and the receptive field characteristics although other differences were also observed. The fields had very sharp borders for the majority of the slowly as well as the rapidly adapting units. The field sizes varied considerably: between 10 mm2 and 600 mm2. For a minority of the receptors, slowly as well as rapidly adapting ones, the receptive fields were constituted of a center of high sensitivity and a wide surrounding area of lower sensitivity without distinct borders. The four types of receptors encountered in the present study have striking similarities with four different types of mechano-receptors which have been described in sub-human primates, namely the type I and type II slowly adapting, intradermal receptor, according to Iggo's terminology, an intradermal rapidly adapting receptor and the Pacinian corpuscle which is located in the subcutaneous tissues. Roughly 75% of the units were slowly adapting. This is a much larger proportion than found in the monkey. Further, it was shown how the recording method offers the opportunity to analyse the perceptive responses as well as the neurophysiological responses in first order neurons to mechanical stimuli.