Biomedical subjects

R Ekedahl

Publications and source records attributed to R Ekedahl.

10 recordsLinked to original sources

PubMed1999

Clustering of Pacinian corpuscle afferent fibres in the human median nerve.

To further study the functional organisation of human peripheral nerves, the intrafascicular arrangement of afferent fibres supplying Pacinian corpuscles (PCs) was explored by percutaneous microneurography using thin-calibre, concentric needle electrodes. In normal adults, 20 PC afferents were identified in 13 recording sites. Low-amplitude (less than 30 microm) vibratory stimuli to the skin were applied with tuning forks oscillating at 128 Hz or 256 Hz and response patterns of individual PC units were studied. In many recording sites, two, sometimes even three, PC afferents with adjacent or overlapping receptive fields in the hand were clustered in the nerve. The observed incidence in the records containing a certain number of PC units was compared with the expected probability calculated according to the hypothesis that all nerve fibres are randomly organised in peripheral nerves. The results suggested that PC afferents are partially segregated in the nerve. In addition, PC afferents were neighbouring on slowly adapting type II (SAII) units and skin sympathetic activity in individual fascicles. SAII units often innervated the same skin area as PC units, but did not respond to vibration. The data provided additional information regarding the functional organisation of the human peripheral nerve and the mechanisms underlying the sense of vibration in man with special regard to population behaviour of neighbouring PC mechanoreceptors.

Adult↗

PubMed1998

Consistency of unitary shapes in dual lead recordings from myelinated fibres in human peripheral nerves: evidence for extracellular single-unit recordings in microneurography.

Percutaneous microneurography is a powerful technique allowing studies of activity in single nerve fibres of conscious humans. However, the mechanisms by which single-unit recordings are achieved with this technique are not fully understood. To further elucidate these mechanisms, dual-lead recordings, using a modified concentric needle electrode with two separate recording surfaces at the tip, were performed in normal subjects. Sixty-two single units supplied by large myelinated afferents were studied. The majority (90%) of the units were recorded simultaneously on both surfaces but with different action potential amplitudes. Four types of unitary waveforms were encountered. The potentials recorded on the two channels were of the same type, although occasionally some details differed. Parallel waveform changes of the same units occurred simultaneously on the two surfaces. A displacement of a single fibre from one recording surface to the other with or without concomitant waveform-type transitions was observed when the electrode was slightly repositioned intraneurally. The results provided direct evidence to confirm that concentric needle electrodes record single-unit activity extracellularly from myelinated nerve fibres, probably at or close to a node of Ranvier. All the types of action potentials encountered with conventional tungsten electrodes were also identified in dual-channel recordings with concentric electrodes, which casts doubt on the previous explanation that single-unit activity recorded with tungsten electrodes is derived from intracellular sources. Some biological and technical aspects of the findings are discussed, especially concerning the applicability of in vivo measurements of the time course of the action potentials in humans and ways to improve microneurography towards multichannel recordings.

Action Potentials↗

PubMed1998

Clustering of slowly adapting type II mechanoreceptors in human peripheral nerve and skin.

The intrafascicular organization of human peripheral nerves was studied with percutaneous microneurography in the median, radial and peroneal nerves with one-surface or two-surface thin diameter concentric needle electrodes. Data from 33 recording sites containing 47 slowly adapting type II (SAII) units were analysed. At many sites two, sometimes even three, neighbouring SAII units were recorded from the explored nerve fascicle and they had adjacent or even overlapping cutaneous receptive fields. Among pairs of SAII units found at the same site, one unit often had ongoing discharge, whereas the other was silent under resting conditions. The neighbouring SAII units were optimally activated by stretching the skin in different directions. Stretching the same skin area in different directions produced different unit recruitment. Clustered SAII units were often found in sites where Pacinian afferents and skin sympathetic activity were also recorded. No significant difference was observed in the degree of grouping of SAII units either between recordings obtained with one-surface versus two-surface electrodes or between glabrous and hairy skin. The data do not support the notion that myelinated fibres are randomly organized in peripheral nerve fascicles. Instead, the findings suggest that SAII units tend to be clustered in human peripheral nerves. Furthermore, the response of groups of SAII units to skin stretch suggests that they play a role in proprioception. Dual channel recordings with two-surface concentric needle electrodes may provide a novel approach to study fibre organization in human peripheral nerves and the behaviour of groups of nerve fibres.

Adaptation, Physiological↗

PubMed1997

Waveform complexity of unit activity recorded with concentric needle electrodes from human peripheral nerves.

Using standardised concentric needle electrodes 170 single units were recorded from myelinated cutaneous afferents in the human median or ulnar nerves. The unitary waveforms were of four types: single-peaked monophasic 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 other types. Units of different functional classes had similar waveforms and there was no specific type of waveform distribution in any particular unit category. In some recording situations there were changes in unitary waveforms from one type to another. There was a tendency for the complex type IV, type III and type II waveforms to change to the simple type I. Adjustment of the electrode often provoked such waveform changes. The waveform profiles and waveform changes observed during recordings with concentric needles were significantly different from those encountered with conventional tungsten electrodes, which might be due to differences in recording properties between the two electrodes. Possible neural mechanisms underlying the observed waveforms and waveform transitions are discussed. In particular, our data suggest that concentric needle electrodes record single-unit activity from myelinated fibres extracellularly.

Action Potentials↗

PubMed1997

Peripheral afferents with common function cluster in the median nerve and somatotopically innervate the human palm.

Concentric needle electrodes with a central core diameter of 20-30 microm were used to explore median nerve fascicles in man. Such electrodes can simultaneously monitor subtle electrophysiological and topographical features even within parts of a fascicle. Single-unit recordings from myelinated fibres were more easily obtained at some intrafascicular sites than others. Typically, groups of identified myelinated fibres in these regions, possibly corresponding to a cluster of Ranvier nodes, tended to be fibres responding to stimuli of the same modality. These afferents innervated the glabrous skin of the human hand and fingers in a somatotopic manner. In particular, the somatotopy even seemed to be present at the receptor level in the skin. This novel aspect of peripheral nerve organisation is probably of fundamental importance for the interplay between peripheral and central processes involved in somatosensation both under normal conditions and in disease. Some clinical implications of the findings are discussed.

Adult↗

PubMed1996

Multiple action potential waveforms of single units in man as signs of variability in conductivity of their myelinated fibres.

Percutaneous microneurography was performed with concentric needle electrodes to record neural activity from myelinated fibres in human peripheral nerves. Template matching techniques were used together with interspike interval analysis and studies on functional class, receptive field characteristics, conduction velocities and other single fibre properties to classify single units. Sometimes the same fibres exhibited different action potentials at the same time. The potentials had some common features, but differed either in their waveform types or only in duration. There was a correlation between the occurrence of the different potential shapes and firing frequency of the studied unit. The outcome of the studies suggested that there was a common denominator which could explain the observations. Most likely, momentary fluctuations in excitability of the myelinated fibres occurring during the relative refractory period or the supernormal period were responsible for the variations in complexity of the studied units due to a partial block of fibre propagation probably caused by the recording electrode. Thus, action potentials deriving from the same axon may not always have the same shapes. Methods for unit classification, such as template matching, are discussed in the light of our findings.

Action Potentials↗

PubMed1996

Demonstration of a fibre afferents with overlapping receptive fields in humans.

According to previous data peripheral nerves may lack a detailed microanatomical organization. Nevertheless, stimuli within restricted skin areas might excite more than one afferent of the same modality. Since, as recently demonstrated, peripheral myelinated afferents are at least partially organized by both modality and somatotopy it might be possible to demonstrate such a phenomenon electrophysiologically provided that adequate procedures are used. To address this issue we recorded activity in single myelinated afferents supplying the hand with concentric needle electrodes. A combination of electrical and/or natural stimuli applied to the area where rapidly adapting (RA) or slowly adapting type I (SAI) fibres ended demonstrated that fibres of the same functional class may exhibit overlapping receptive fields in the skin.

Action Potentials↗

PubMed1996

Single unit discrimination among discharges from neighboring myelinated fibers in human peripheral nerves: improved unit identification by interspike interval analysis of nerve responses evoked by tactile stimuli.

Clustered rapidly adapting (RA) or slowly adapting type I (SA I) units recorded with concentric needle electrodes from median nerves of healthy human volunteers may exhibit overlapping receptive fields in the skin as also Paccini afferents (PC units) and slowly adapting type II unitary elements (SA II units) with their much larger innervation areas. Fundamental for the discrimination of such pairs of neighboring units in the nerve with overlapping peripheral fields was the refractory period of the studied fibers, which was assumed to be normal, i.e., of the order of 1-2 ms. When a unit belonging to one of the categories mentioned was found, it was activated by different tactile stimuli in the palm or fingers. Simultaneously, interspike interval analysis of the evoked responses was performed. In situations when the minimal interspike intervals were longer than the absolute refractory period of a single fiber the response derived from one single unit. Responses from at least two units were considered to contribute to the recorded sequences when computer analysis showed that the durations of the minimal intervals were shorter. In this way, the reported procedure facilitated the discrimination of both pairs of RA and SAI units and, in particular, pairs of neighboring PC or SA II units with overlapping receptive fields in human palmar skin.

Adolescent↗

PubMed1994

Electrophysiological evidence of Ranvier node clustering in human sensory nerve fascicles.

Thin concentric needle electrodes were used to explore intact median nerve fascicles in human subjects. In particular, the presence of single units, probably recorded from nodes of Ranvier, was studied in different parts of a fascicle. Single-unit activity in myelinated fibers was rarely found at numerous sites. In many other intrafascicular areas, a substantial number of single units could be discriminated in the same or nearby recording sites with the same technique. To account for the neurophysiological results, stochastic models and statistical tests were developed to test various hypotheses concerning intrafascicular nerve fiber arrangements. The acquired data suggested both an intrafascicular modality grouping of nerve fibers and a simultaneous clustering of the Ranvier nodes of these fibers within very restricted areas of a fascicle. It was further concluded that the yield when searching for units in different types of nerve preparations may depend upon the ultrastructure of the explored nerve segments.

Adult↗

PubMed1991

Segregation by modality of myelinated and unmyelinated fibers in human sensory nerve fascicles.

Thin diameter concentric needle electrodes with a small recording surface were used to explore the characteristics of neighboring fibers in sensory median nerve fascicles. Fibers which were close neighbors in the fascicle, were not randomly distributed intraneurally. Instead there was an intrafascicular segregation by modality of both myelinated and unmyelinated fibers. In addition, evidence was obtained which suggested that the contents of different Schwann cells vary. Some Schwann cell systems envelop afferent C fibers whereas others hold efferent sympathetic C axons. The results imply a modality segregation amongst both A and C fibers in human peripheral sensory nerve fascicles.

Adult↗