398 



HANDBOOK OF I'HYSIOLOG"!' 



XEl'RnpHVSIOLOGY I 



FIG. 2. Topical organization of libers in the posterior column 

 and in the posterior column nuclei. The upper two cross sec- 

 tions (M) refer to the medulla, the lower five to the coccygeal 

 (I. Co.), sacral (I. S.), lumbar (I. L.), thoracic (II. Th.) and 

 cervical (I. C.) levels of the spinal cord. The relative positions 

 of fibers are indicated by dots for the coccygeal fibers and by 

 crosses, dashes, dots and dashes and triangles for fibers of 

 successively higher segments, i : nucleus gracilis; 2 to 4: com- 

 plex of nucleus cuneatus; 7 : descending root of the fifth nerve. 

 [From Glees et al. (97).] 



columns following section of dorsal roots, or transec- 

 tion of the dorsal columns al various levels, indicates 

 that the centrally projecting fibers are arranged in an 

 orderly lamination (43, 65, 66, 70, 97, 258). Those 

 from each successively higher segment are arranged 

 in a series of successively more lateral laminae of fibers 

 (fig- 2). 



Patterns in Dorsal Column Nuclei 



As figure 2 shows, this precise lamellar arrangement 

 of the fibers of the dorsal cohunns is unchanged in the 

 dorsal column nuclei. Fibers from the caudal seg- 

 ments terminate in the most medial portion of nucleus 



gracilis, those from sacral, lumbar and at least the 

 lower six thoracic roots terminate in successively 

 more lateralis' placed dorsoventrally directed lamel- 

 lae. Glees et al. Qqj') belie\^e that all thoracic roots 

 with the exception of the first terminate in this 

 nucleus. Fibers from the upper thoracic and from the 

 cervical roots terminate in nucleus cuneatus in a 

 similar lamellar arrangement. Other fibers of the 

 upper thoracic and of the cervical roots ascend in the 

 dorsal columns and terminate in a topographically 

 arranged pattern in the lateral cuneate nucleus, 

 whose cells in turn project upon the cerebellar cortex. 



The Marchi material suggests the existence of a 

 considerable overlap between the terminals of neigh- 

 boring fibers. However, it has been shown (97, 98) by 

 using silver staining methods that intersegmental 

 overlap is minimal, though intrasegmental overlap 

 of the fields of termination occurs. This latter is 

 accentuated by the numerous branching dendrites 

 which reach into the synaptic fields of neighboring 

 cells. The linage of the body form thus composed by 

 this projection is distorted to allow greater volume 

 representation for those body parts which are heavily 

 innervated by afferent fibers. 



One looks to electrophysiological methods for finer 

 details of the representation pattern. The lamination 

 pattern in the dorsal columns has been confirmed 

 (280). It appears, however, that only one study has 

 been made of the projection pattern in the dorsal 

 column nuclei, and that has been reported in only a 

 short note. Using physiological stimuli Kuhn (145) 

 has mapped the projection of the body surface upon 

 the dorsal column nuclei. He found the ipsilateral 

 body surface of the cat to be represented within the 

 caudal portions of the dorsal column nuclei as an in- 

 verted figure of the animal, with the tail pointed 

 dor.socaudally, extremities dorsally. No responses were 

 recorded following stimulation of the contralateral 

 side. 



Unfortunately there are no experimental data to 

 indicate the pattern of projection of the first order 

 neurons of the trigeminal nerve upon the cells of the 

 main sensory nucleus of the fifth. That a detailed and 

 well differentiated pattern must exist therein is indi- 

 cated by the pattern formed by the terminals of the 

 second order elements within the thalamic relay 

 nucleus (see fig. 3). This latter pattern contains also 

 an ipsilateral projection of the peri- and intraoral 

 structures which are partially superimposed upon the 

 contralateral pattern of representation of the same 



