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The bases of bioelectrical activity are different ionic concentrations inside and outside the membranes of the nerve and muscle cells. The concentration gradients for Na+, K+, and Ca2 + are maintained by ionic pumps in the membranes. Another type of macromolecules in the membrane is responsible for opening and closing channels selectively for the diffusive passage of ions involved. As a consequence, either equilibrium (diffusion) or resting membrane potentials are established. If the membrane is depolarized by a stimulus beyond a threshold, electrical impulses, called action potentials, occur and may be propagated over long distances. At the sensory and subsynaptic membranes, sensor and synaptic potentials are generated, which are conducted passively over short distances. For scientific, but mostly for diagnostic, purposes, differences of potentials may be recorded very conveniently from the body surface, using skin electrodes and appropriate amplifiers and filters. The measured potentials are due to integrative activity of several cells: electromyogram recording electrical muscle activity; electroneurogram displaying neuronal; electroencephalogram and evoked potential, cortical; electrocardiogram, cardiac; and electroretinogram, retinal.

The electroneurogram (ENG) recorded from glabrous skin nerve, muscle nerve or mixed nerve in cats has demonstrated that relevant and reliable information is present in natural sensors, suitable for feedback regulation of Functional Neuromuscular Stimulation (FNS) systems. In this study we demonstrate that it is possible to make whole nerve cuff electrode recordings from a human cutaneous nerve innervating the glabrous skin mechanoreceptors, and that the nerve cuff recordings contain information about changes in a force applied to the skin. The simple and reliable neurosurgical procedure, and the unique consistency in the recordings with findings from animal studies makes this technique a feasible option for feedback regulation of implanted FNS systems, suitable to restore hand function, gait and stance in spinal cord injured subjects.