STUDY ON THE THERMAL RECEPTION BY APPLICATION OF ACTION POTENTIALS OF CUTANEOUS NERVE IN FROGS

The activity of the cutaneous thermoreceptors in a certain area was investigated by an indicator of the afferent impulses in one nerve bundle.Thermal stimulus was applied to a skin-nerve preparation consisted of the dorsal skin and a dorsal cutaneous nerve of frogs with the thermal stimulator deviced by the author. The change of response shown by the manifestation of afferent impulses was analyzed. The following results were obtained.(1) The thermoreceptor responsible for the change in environmental thermal condition was recognized.(2) This type of receptor was less than the receptor of touch or pressure in number.(3) The distribution of one dorsal cutaneous nerve bundle was approximately 10mm in radius.(4) The extent of the indifferent temperature of the thermoreceptors moved in parallel with the atomospheric temperature. The extent of the indifferent temperature in 15 to 25°C of the room temperature became ±3°C wider than the latter extent.(5) The thermoreceptors responded to the thermal stimulation from about 5 to 40°C.(6) Thermal stimulation higher than the indifferent temperature caused the small impulses, and that lower than the indifferent temperature resulted in the large impulses. These impulses tended to increase with departing from the indifferent temperature.(7) Even at the same temperature the response varied by the direction of the increased or decreased intensity of stimulus.The author wishes to express the gratitude to Professor K. Suenaga, M. D. for the direction and advice, and also to all members of Department of Physiology for their various helps during the course of the study.