PAIN 



487 



physiopathologic counterpart. <) That the dorsal 

 columns may, however, even if only rarely, carry 

 impulses causing clinical pain seems a tenable hy- 

 pothesis from the results of Browder & Gallagher 

 (35). Their operative division of the dorsal column 

 relieved, in three of four patients, pain referred to a 

 phantom lower limb which seemed to be in a dis- 

 torted posture. Moreover, tingling sensations per- 

 haps like those evoked on posterior column stimula- 

 tion may occur in the analgesic limb after cordotomy 

 upon an unusually no.xious event, such as running 

 a nail into the foot. 



.MEDULLA OBLONGATA 



The primary afferent neurons for pain and tem- 

 perature arising from the face and head via tri- 

 geminal, nervus intermedius, glossopharyngeal and 

 vagal routes collect in the descending or spinal 

 trigeminal tract and terminate near cells in the 

 lower part of the nucleus of that tract. The cells in 



this position extending froin about the obex down- 

 ward were called by Winkler the nucleus gelatinosus 

 tractus spinalis (302, pp. 51 to 59) because they 

 resemble those of the substantia gelatinosa Rolandi 

 of the spinal cord. Olszewski's (202^ more recent 

 careful study of the nucleus in man and monkev is 

 in general agreement. Section of the descending 

 tract at about the level of the obex usually produces 

 trigeminal analgesia as well as severe hypalgesia of 

 the deeper areas of the face and head supplied by 

 the afferent fibers in the seventh, ninth and tenth 

 cranial nerves; so the correlation of the 'subnucleus 

 gelatinosus' of Olszewski with pain and temperature 

 function seems likely. Evidence on these points as 

 well as on the finer details of topographic localization 

 of the fibers from various portions of the head and 

 face within the tract and their termination in the 

 nucelus are summarized by White & Sweet (296, pp. 

 457 to 466). 



The locus of spinothalamic fibers ascending from 

 the secondary afferent neinons of the cord as de- 

 termined by Marchi stain is illustrated in figure 9. 



4lh Ventricle 



Bulbo- 



T ha 1 om I 



Troct 



Spinocerebellar 

 Troct 



Lot erol 



Spi notholo mic 



Troct 



Mediol Lcnniicoi 



nttrior Oliv* 



FIG. 9. Degeneration in the spinothalamic and bulbothalamic tracts at level of the inferior olive. 

 The Marchi degeneration in the lateral spinothalamic tract (including spinotectal fibers) is that 

 seen by Kuru in a patient all of whose pain fibers in the anterior half of the cord below C4 segment 

 had degenerated. We show the locus of the bulbothalamic tract as that area of absence of Weigert- 

 stained fibers described by Wallenberg in a patient who had post-mortem a softening in the ventral 

 two-thirds of the descending trigeminal tract and its nucleus. The ictus had occurred 5 years earlier; 

 the infarct it produced was of maximal size at the level of the obex, i.e. about the rostral end of the 

 nucleus for pain fibers. We have referred to the secondary afferent pathway from this area as the 

 bulbothalamic rather than trigeminothalamic tract since it probably includes the area of nervus 

 intermedius, glossopharyngcus and vagus as well as trigeminus. [Modified from Kuru (149).] 



