178 INTRODUCTION TO NEUROLOGY 



with the proprioceptive group of reactions. These may be 

 unconscious reflexes of motor coordination and the maintenance 

 of equilibrium, or they may come into consciousness as sensa- 

 tions of position and orientation of the body and its parts and of 

 spatial discrimination. Purely exteroceptive stimuli, whether 

 transmitted by the deep nerves or by the cutaneous nerves, may 

 be carried for a few segments in the dorsal funiculi (Fig. 81, 

 neuron 1); but they are soon filtered off into the gray matter of 

 the dorsal column, and after a synapse here they are sorted into 

 functionally distinct tracts on the opposite side of the cord. 

 The tactile elements of the mixed peripheral root fibers entering 

 the dorsal funiculus are drawn off later than are the elements for 

 thermal and painful sensibility; and some of the components 

 commonly reckoned with cutaneous exteroceptive sensibility 

 remain in the dorsal funiculus for its entire length. These are 

 chiefly two-point discrimination, and discrimination of size, 

 shape, form, and texture of surfaces. These all involve a com- 

 parison and discrimination in consciousness of spatial factors 

 and are, therefore, bound up with those fibers which serve the 

 proprioceptive reflexes, which are unconscious spatial adjust- 

 ments. 



Some peculiar combinations of symptoms arise from the fact 

 that, whereas the ascending proprioceptive impulses (so far as 

 these are consciously perceived) pass up in the dorsal funiculus 

 of the same side for the entire length of the cord, the impulses 

 of the exteroceptive impulses, within a few segments of their 

 point of entrance into the cord, are transferred to the opposite 

 side to ascend in the spinal lemniscus tracts. From this it fol- 

 lows that a localized central injury involving the dorsal gray 

 column and dorsal funiculus of one side only will cut off all 

 ascending proprioceptive impulses which pass through the dor- 

 sal funiculus from lower levels on the same side of the body as the 

 lesion, and at the same time will abolish both proprioceptive and 

 exteroceptive functions in a circumscribed region of the same 

 side of the body whose exteroceptive neurons of the first order 

 discharge into the injured part of the dorsal gray column. 



Figure 84 illustrates the loss of sensibility to painful stimuli 

 resulting from a tumor in the cervical region of the spinal cord. 

 Tactile, temperature, and deep sensibility were also profoundly 



