抄録
Recent advance in electrophysiological studies have shown that there exist mechanical nociceptors which respond only to mechanical nociceptive stimuli such as pin indentation. Such mechanical nociceptive stimulus generates some mechanical deformation of the skin, and the nociceptors may respond to this deformation. That is when we have the sensation of pain. However, it is difficult to identify the mechanical factor as the direct adequate stimulus for pain reception. Therefore, the mechanical factor for prick pain sensation has been investigated by computer simulation of the elastic model of the skin. Referring to free nerve endings in the epidermis, pain receptors in the model were assumed to be scattered pseudorandomly within the skin at a certain depth. When the skin was regarded as being a semi-infinite uniform elastic medium, mechanical factors such as stress and strain at the pain receptors could be computed by applying three dimensional elastic theory. For six kinds of stimulus needles, “indentation thresholds”, indentation amplitude of the needle from the skin surface to the depth where the mechanical factor of one of the receptors exceeds the threshold of the receptor, and pain intensity at the threshold, which is defined as logarithm of transition velocity of the mechanical factor, were predicted by computer simulation. In all, twenty five kinds of mechanical factors were examined as the candidates of adequate stimulus. The results of the simulation were compared with the results of psychophysical experiments on human subjects. Among the candidates, vertical differential of vertical compressive strain and vertical differential of averaged horizontal tensile strain showed the best agreement between simulation and experimental results of both indentation threshold and pain intensity. This suggests that the differential of circumferential strain have the possibility of being the adequate mechanical factor for the sensory reception of pain.
