484 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. 7. Termination of pain fibers of the posterior root in 

 human spinal cord. Large fiber A passes through the substan- 

 tia gelatinosa to terminate near a cell of nucleus proprius. 

 Small fiber C ends within substantia gelatinosa in relation to 

 either: a pericornual cell, a cell of nucleus proprius, or a small 

 cell within the substantia gelatinosa. Long axons crossing in 

 the anterior commissure and ascending the cord arise from the 

 nucleus proprius or pericornual group. [Modified from Pear- 

 son (207).] 



cells lying in three main groups around the margin 

 of the posterior horn, a special group at its dorsal 

 tip, a reticular or lateral group adjoining the pos- 

 terolateral column of white matter and an inner 

 medial group adjoining the posterior white column. 

 These extend the full length of the cord, and Kuru 

 concludes that they give rise to the pain and tem- 

 perature fibers (149, pp. 10 and 11). He has studied 

 the retrograde cell degeneration in the posterior 

 horns of patients who have had anterolateral cor- 

 dotomy, with attention to those who have had in- 

 complete analgesia and thermanesthesia below the 

 expected level. He found a striking correlation be- 

 tween the segments of the cord showing chromatoly- 

 sis of the pericornual cells and the dermal segments 

 showing loss of pain and temperature sensation. The 

 patients in whose pericornual cells below the level 

 of operation he saw the greatest chromatolysis also 

 had the greatest degeneration in the lateral spino- 

 thalamic tract. The larger cells occupying the more 



centrally placed nucleus proprius of the posterior 

 horn were not degenerated unless the anterior white 

 columns were cut. They did show chromatolysis, 

 however, in three patients whose incisions included 

 the anterior white matter. In the.se three patients he 

 traced degeneration in a distinct ventral spino- 

 thalamic tract, which he did not associate with loss 

 of pain and temperature. 



Anatomical details as to the number of segments 

 required for crossover of the pain fibers through the 

 anterior commi.s.sure, the likelihood of some fiJDers 

 remaining uncrossed and the consistency with which 

 fibers from a given area of the body occupy a par- 

 ticular portion of the opposite anterior quadrant 

 of the cord are of great importance to the surgeon 

 seeking to relieve pain but need not engross us here. 

 White & Sweet (296, pp. 37 to 45) may be consulted 

 for details. 



Although the association of pain fibers with tho.se 

 for temperature in the anterior white quadrant is a 

 close one there are a number of recorded results of 

 dissociation of loss of pain from that of temperature. 

 Analgesia to pinprick with little or no thermanes- 

 thesia was recorded following small, fractionally 

 enlarged incisions for anterolateral cordotomy by 

 Wilson & Fay (299) in one of two cases, by Stookey 

 (255) in four cases, by Grant (no) in one case and 

 by Foerster & Gagel (80) and Kuru (149) in 3 of 30 

 cases. The converse state of severe hypothermesthesia 

 with preservation of normal pain sense has also 

 been recorded by Frazier & Spiller (83) in a pa- 

 tient with a midcervical cord tumor. The paucity 

 of .such observations indicates that there usually are 

 not two distinct bundles of fibers for pain and tem- 

 perature, but the fact that such dissociation can oc- 

 cur suggests that individual fibers are concerned 

 with impulses either for pain or for temperature. 

 Such a thought is further intimated by the observa- 

 tion of Sweet (259) that bipolar electrical stimula- 

 tion within the anterior half of the cord in man 

 elicited responses purely of temperature (usually 

 heat) in 46 per cent of the responses in which any 

 subjective sensation occurred. The usual response 

 was one of pain with or without a burning quality 

 in 54 per cent of 200 stimulations 



A number of factors have conspired to make 

 physiologic studies of pain in the central nervous 

 system even more difficult than those of the periph- 

 eral somatic and autonomic systems. As mentioned 

 earlier, pain pathways in the cords of animals ap- 

 pear to be more difTusely distributed and to ascend 

 by multiple relays with cro.ssing and recros.sing of 



