Aetiology and Laboratory Diagnosis
Raimo E Suhonen, Rodney P R Dawber, David H Ellis in Fungal Infections of the Skin, Hair and Nails, 2020
Dermatophytosis of the scalp, glabrous skin and nails is caused by a closely related group of fungi known as dermatophytes which have the ability to utilise keratin as a nutrient source, i.e. they have a unique enzymatic capacity. It is important to stress that fewer than 50% of dystrophic nails are of fungal aetiology and that it is therefore essential to establish a correct laboratory diagnosis by microscopy and/or culture before treating a patient with a systemic antifungal agent. For a laboratory diagnosis, clinicians should be aware of the need to generate an adequate amount of suitable clinical material. In patients with suspected dermatophytosis of the nails, the nail plate should be pared and scraped using a blunt scalpel until the crumbling white degenerating portion is reached. Therefore, it is essential to perform both direct microscopy and culture on all specimens, and repeat collections should always be considered in cases of suspected dermatophytosis with negative laboratory reports.
SOFT TISSUE COVERAGE OF THE HAND AND UPPER EXTREMITY
Alex P. Jones in Essentials of Plastic Surgery, 2016
A. Full-thickness grafts are best harvested from the contralateral upper limb. B. The heel is a good donor site for glabrous skin graft harvest. C. Split-thickness skin grafts should be meshed to improve graft take. D. It is normal for glabrous skin grafts to appear sloughy at 1 to 2 weeks. E. Split-thickness skin grafts will contract more immediately after harvest than full-thickness grafts.
Vibrotactile thresholds at the sole of the foot: Effect of vibration frequency and contact location
Published in Somatosensory & Motor Research, 2011
Studies of vibration perception in the glabrous skin of the human hand have identified four mechanoreceptor channels, with each channel showing characteristic variations in thresholds with variations in the frequency of vibration and the area of vibration excitation. To advance understanding of the channels mediating vibration perception on the sole of the foot, this study determined how thresholds depend on the frequency of vibration, the location on the foot (the big toe, the ball of the foot, and the heel), and the gap between a vibrating probe and a fixed surround. Thresholds at the three locations were obtained at the 12 preferred one-third octave centre frequencies from 20 to 250 Hz using a 6-mm diameter probe with both a 10-mm and a 20-mm diameter surround. With the 10-mm surround, the displacement thresholds at all three locations showed flat responses from 20 to 40 Hz. With both the 10-mm and the 20-mm surround, the displacement thresholds at the three locations showed “U-shaped” responses from 40 to 250 Hz. Relative to thresholds obtained with the 20-mm surround, thresholds obtained with the 10-mm surround were lower at the toe and the heel with 20- and 25-Hz vibration, but higher at the ball of the foot with 31.5- to 250-Hz vibration. It is concluded that absolute thresholds for the perception of vibration at the sole of the foot show important variations with location and with contact conditions and tend to be mediated by the NP I channel in the range from about 20 to 40 Hz and the P channel from about 40 to 250 Hz.
Mechanoreceptors in the Glabrous Skin of the Human Hand
Published in Archives Of Physiology And Biochemistry, 1999
Since the first systematic analysis concerning the functional properties of mechanoreceptors in the glabrous skin of the human hand was made in 1970, the amount of available data has grown tremendously. Whereas the first research in the seventies was aimed at achieving a standard functional description of the mechanoreceptors, research of the last two decades mostly has been directed towards developing a more detailed and extended model of these receptors. For example, recent investigations attempted to examine the role of populations of mechanoreceptors with respect to the recognition of texture and shape of an object touched by the human hand. Knowledge of the behaviour of the mechanoreceptive units in the glabrous skin of the human hand is especially relevant to people with a diminished or lost vision who depend on their tactile system to perceive objects they cannot hear or smell. This essay tries to give a brief overview of the development of this field from the first experiments on human beings to the state of knowledge that has been gained today.
Asymmetric response properties of rapidly adapting mechanoreceptive fibers in the rat glabrous skin
Published in Somatosensory & Motor Research, 2013
İsmaıl Devecıoğlu, Burak Güçlü
Previous histological and neurophysiological studies have shown that the innervation density of rapidly adapting (RA) mechanoreceptive fibers increases towards the fingertip. Since the psychophysical detection threshold depends on the contribution of several RA fibers, a high innervation density would imply lower thresholds. However, our previous human study showed that psychophysical detection thresholds for the Non-Pacinian I channel mediated by RA fibers do not improve towards the fingertip. By recording single-unit spike activity from rat RA fibers, here we tested the hypothesis that the responsiveness of RA fibers is asymmetric in the proximo-distal axis which may counterbalance the effects of innervation density. RA fibers (n = 32) innervating the digital glabrous skin of rat hind paw were stimulated with 40-Hz sinusoidal mechanical bursts at five different stimulus locations relative to the receptive field (RF) center (two distal, one RF center, two proximal). Different contactor sizes (area: 0.39, 1.63, 2.96 mm2) were used. Rate-intensity functions were constructed based on average firing rates, and the absolute spike threshold and the entrainment threshold were obtained for each RA fiber. Thresholds for proximal stimulus locations were found to be significantly higher than those for distal stimulus locations, which suggests that the mechanical stimulus is transmitted better towards the proximal direction. The effect of contactor size was not significant. Mechanical impedance of the rat digital glabrous skin was further measured and a lumped-parameter model was proposed to interpret the relationship between the asymmetric response properties of RA fibers and the mechanical properties of the skin.
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