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INTRODUCTION TO NEUROLOGY 



diately upon entering the spinal cord divides into ascending and 

 descending branches, and secondary branchlets are given off in 

 large numbers from each of these, so that a single peripheral 

 sensory neuron may discharge its nervous impulses into very 

 many central neurons scattered throughout the entire length of 

 the spinal cord. When to these numerous endings we add the 

 countless ramifications of the correlation neurons, it is evident 



-spinal lemniscus 

 correlation neuron 1 

 funiculus dorsalis 



sp.g.l 

 correlation neuron, 2 



sp.g.3 



correlation neuron 3 

 ( ) spg.4 



Fig. 61. Diagram of the spinal cord reflex apparatus. Some of the con- 

 nections of a single afferent neuron from the skin (d.r.2) are indicated : d.r.2, 

 Dorsal root from second spinal ganglion ;m, muscles; sp.g.l to sp.g.4, spinal 

 ganglia; v.r.l' to v.r.4, ventral roots. 



that even in the spinal cord, which is the simplest part of the 

 central nervous system, there are reflex mechanisms of great 

 complexity. Some of these have been analyzed. Sherrington, 

 in his Integrative Action of the Nervous System, has presented 

 a very clear analysis of the scratch reflex of the dog and the 

 neural mechanisms involved. The mechanism of the locomotor 

 reflexes has been studied physiologically and histologically by 



