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Microneurographic recordings from cutaneous receptors from the lower limb of humans Kennedy, Paul Michael

Abstract

Postural control is achieved through complex interactions between different neural networks. While it is difficult to isolate the contribution of any individual system, somatosensory information from the lower limbs provides a sensitive measure of postural sway during quiet stance (Fitzpatrick and McCloskey 1994). Furthermore, these signals initiate postural responses to perturbations to permit accurate realignment of the body after a disturbance in stance (Inglis et al. 1994). One possible source of this essential information, although not clear, is thought to originate in cutaneous mechanoreceptors located in the glabrous skin of the foot sole. To date, there is limited information about the cutaneous afferents in the lower limb. The purpose of this study was therefore to document the characteristics of these receptors and to examine their potential role in postural control. Thirty-one recording sessions were performed on thirteen conscious participants between 22-50 years of age. Single unit activity was recorded from the tibial nerve at the level of the popliteal fossa with tungsten electrodes inserted percutaneously in the lower limb. Stable single unit recordings typically lasted between 10-15 minutes despite small ankle movements. Receptors were classified as slowly (SA) and fast adapting (FA) based on their response to a sustained indentation of the skin. Iri accordance with previous investigations the units were subdivided based on the properties of their receptive fields; small, well defined (type I) and large with obscure borders (type II). The proportion of the different receptor types (14% SAI, 15% SALT, 60% FAI, 14% FAIL n = 106) demonstrates that the glabrous skin of the foot sole potentially has a higher dynamic sensitivity than other documented skin regions (i.e. hand). The low degree of static activity in the foot sole could argue towards a sampling bias. However, the interpretation of the data is that this is of functional importance because during quiet stance maintaining stability is a dynamic task since the body is never completely motionless (Horak and Macpherson 1996).

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