Somatosensory System pp 29-78
Cutaneous Mechanoreceptors and Nociceptors
Although information from sense organs is used by all animals, only man can verbally report his sensory experience. A brief consideration of these experiences may be useful in providing insight into cutaneous sensory mechanisms. Nonnoxious deformation of the human skin with a stimulator having a small surface area (2–3 mm2) evokes sensations usually referred to as “touch”. If the stimulator remains stationary, the sensation fades. Movement of the stimulator perpendicular to the skin produces changes in the sensory process which allow even rapidly repeated stimuli (e.g. 500 Hz) to be distinguished from stationary ones. When larger stimulators are used, some appreciation of texture can be obtained, and this is enhanced by movement of the stimulating surface across the skin. A smooth stimulator or an insect moving slowly and gently over the skin evokes distinctive sensations usually referred to as “tickle”. A sharp object such as a pin lightly pressed against certain points in the skin leads to an unpleasant experience which differs from touch but is equivocally painful; when the pin is pressed against the skin more firmly it usually elicits pain. Thus, sensations induced by mechanical events can be diverse. Moreover, common experience indicates that they may occur with greater or lesser intensity. On the other hand, neurophysiological experiments defining the properties of cutaneous sense organs have most often been done on animals other than man.
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