Physicochemical Characteristics of Soil from Selected Solid Waste Dump Sites in Port Harcourt, Rivers State, Nigeria

Abstract

Using standardised concentric needle electrodes 170 single units wererecorded from myelinated cutaneous afferents in the human medianor ulnar nerves. The unitary waveforms were of four types: single-peakedmonophasic potentials (type I), double-peaked monophasic potentials(type II), biphasic potentials (type III) and triphasic potentials(type IV). Type II and IV occurred more frequently than the othertypes. Units of different functional classes had similar waveformsand there was no specific type of waveform distribution in any particularunit category. In some recording situations there were changes inunitary waveforms from one type to another. There was a tendencyfor the complex type IV, type III and type II waveforms to changeto the simple type I. Adjustment of the electrode often provokedsuch waveform changes. The waveform profiles and waveform changesobserved during recordings with concentric needles were significantlydifferent from those encountered with conventional tungsten electrodes,which might be due to differences in recording properties betweenthe two electrodes. Possible neural mechanisms underlying the observedwaveforms and waveform transitions are discussed. In particular,our data suggest that concentric needle electrodes record single-unitactivity from myelinated fibres extracellularly.