CHAPTER XVIII 



Thermal sensations 



YNGVE ZOTTERMAN 1 Department of Physiology, Veterindrhogskolan, Stockholm, Sweden 



CHAPTER CONTENTS 



STRUCTURE OF RECEPTIVE FIELD 



Structure of Receptive Field 



Topography of Thermal Senses: Cold and Warm Spots 

 Depth of Thermal Nerve Endings 

 Identification of Thermal Receptors 

 Afferent Nerve Paths 

 Conditions for Thermal Sensations 

 Conduction of Heat in Skin 

 Relation Between Temperature Change Recorded in Skin 



and Thermal Sensation 

 Paradoxical Sensations 

 Thermal After -Sensations 

 Sensation of Hot' 

 Electrophysioiogy of Thermal Nerve Fibers 

 Specificity of Nerve Fibers in Mammals 

 Thermal Receptors in Cold-Blooded Animals 

 Quantitative Relations Between Temperature Movements 

 and Nerve Fiber Discharge 

 Methods 



Discharge at constant temperature 

 Cold fibers 

 Warm fibers 

 Response of thermal receptors to temperature changes 

 Cold fibers 

 Warm fibers 

 Paradoxical discharges 

 Effect of temperatures above 47 °C 

 Intracutaneous gradient 



Response of mechanoreceptors to thermal stimulation 

 Influence of Nonthermal Agencies 

 Theoretical Considerations 

 Central Threshold 

 Excitation Mechanism of Thermal Receptors 



The different sensations of cold and warmth are produced by 

 stimulation of separate specific nerve end-organs in the skin. 



Magnus Blix 1882 (9). 



Topography of Thermal Senses: Cold and ]Varm Spots 



SINCE THE DISCOVERY by Blix (9, I o) ol" cold and warm 

 spots from which adequate or electrical stimuli elic- 

 ited cold and warm sensations, respectively, numerous 

 authors have described the distribution of cold and 

 warm spots in the skin as well as in the mucous mem- 

 branes of man. In general cold spots are far more 

 numerous than warm spots, but the relation between 

 the density of the two kinds of temperature sensitive 

 spots varies a good deal in different areas. Hensel (45) 

 in his review emphasizes the great errors inherent in 

 finding these thermal spots by using punctiform 

 stimuli such as Blix's cone affords. The highest density 

 of thermosensitive spots is found in some areas of the 

 face. Particularly sensitive to thermal stimulation are 

 the eyelids and the lips. The forehead is very cold- 

 sensitive but only moderately sensitive to warmth. 

 The hairy parts of the head, the patellar region and 

 the tongue are very slightly sensitive to warmth. The 

 conjuctiva bulbi and the periphery of the cornea 

 possess cold sensitivity but do not respond to warmth. 

 Careful investigations on the distribution of tempera- 

 ture spots have been made for the whole body by 

 Rein (72) and Goldscheider (32), for the genital or- 

 gans by Hauer (39), Speiser (81) and Beetz (6), for 

 the eye by Strughold & Karge (84) and Strughold & 

 Porz (85), and for the mucous membranes of the 

 mouth and the nose by Rein (72), Strughold (83), 

 Schriever & Strughold (jS) and Hirsch & Schriever 

 (59). In these papers as well as in Goldscheider's re- 

 view (32) topographical charts of temperature spots 

 will be found. In table i the mean density of cold 

 and warm spots is given for different areas of the body 

 surface. The high temperature sensitivity of the tri- 



43' 



