TENDON JERKS; SENSOR! PATHWAYS IN SPINAL CORD 



minis, nvusch si a si through tin homolateral dorsal column, whil( tactih 

 sensations pass partly by thi uncrossed fibers of tin dorsal column and 

 partly lm tin oppositi lateral columns. It is interesting thai of tl 

 two paths for tactile impulses the crossed one is alone closely associated 

 with the trad thai carries pain (Holmes . 



Head and Thompson 11 have also found thai the sensations are grouped 

 to the extenl thai those of one kind travel together, whether they are 

 from deep or superficial, from protopathic or epicritic receptors. When 

 the appreciation of cutaneous pain is lost, bo also is thai produced by 

 deep pressure; light touch and heavy touch are also losl simultane- 

 ously. The appreciation of ;ill degrees of temperature is abolished al the 



same ti The ability to discriminate between two points, the apprecia 



tion of \\ri'_ r lit, the recognition of the vibrations of ;i heavy tuning fort 

 applied to the skin- all depend on impulses conducted through the 

 homolateral dorsal columns. 



Because the crossing in the cord of sensory fibers carrying certain sen- 

 sations occurs more promptly than thai of those carrying others, and for 

 other less clearly understood reasons, the clinical findings are "I'i-mi diflficnll 

 of interpretation, especially when the lesions are only partial. Tin- 

 senses of pain and temperature are undoubtedly lost much more readily 

 than those of cutaneous sensibility, though sometimes the reverse con- 

 ditions are found. If a partial lesion of one-half of the cord occurs 

 aboul the level of the twelfth dorsal segment, ;i very common symptom 

 is loss of i»;iin and temperature on the opposite side, bul n<>t of touch 

 even when strong stimuli are applied. This crossed relation does not, 

 however, occur when the lesion is below the twelfth dorsal. 



Regarding the number of segments necessary for the decussation of 

 each kiml of sense fiber, observations on cases in which there is unilal 

 eral injury of the cord are being collected, so thai the npper limit of the 

 anesthetic area maj be compared with the segmental level of the injury, 

 n appears thai pain and thermal impulses cross quickly i. e., within b 

 uegmenl <ir two in the middorsal region, hut thai those of touch cross 

 somewhal nun-.' gradually. In the upper segments the obliquity 

 crossing of both kinds of fibers is greater, and in the cervical region 

 it may require five or six segments for the crossing of pain impulse - 

 With this increasing obliquity, ;i distinction appears in the crossing levels 

 of pain and temperature, for the latter cross a little more quickly. 

 This conforms with the clinical observation thai thermal appreciation 

 may be disturbed without thai of pain. Even the thermal impulses <h> 

 nut .-ill decussate al the same level, for anesthesia t.> heat may reach 

 higher up on the skin area than thai to cold. 



When recoven occurs, the sensations gradually reappear caudalwards 



