26 INTRODUCTION TO NEUROLOGY 



pulse outward from the center to (5) the effector apparatus, 

 consisting of the organs of response (muscles, glands) and the 

 terminals of the efferent nerves upon them. 



No part of the nervous system has any significance apart from 

 the peripheral receptor and effector apparatus with which it is 

 functionally related. This is true not only of the nervous mech- 

 anism of all physiological functions, but even of the centers con- 

 cerned with the highest manifestations of thought and feeling of 

 which we are capable, for the most abstract mental processes 

 use as their necessary instruments the data of sensory experience 

 directly or indirectly, and in many, if not all, cases are inti- 

 mately bound up with some form of peripheral expression. 



The neurologist's problem is to disentangle the inconceivably 

 complex interrelations of the nerve-fibers which serve all the 

 manifold functions of adjustment of internal and external rela- 

 tions; to trace each functional system of fibers from its appro- 

 priate receptive apparatus (sense organ) to the centers of corre- 

 lation; to analyze the innumerable nervous pathways by which 

 these centers are connected with each other (correlation tracts) ; 

 and, finally, to trace the courses taken by all outgoing impulses 

 from these correlation centers to the peripheral organs of re- 

 sponse (muscles, glands, etc., or, collectively, the effectors). 



This is no simple task. If it were possible to find an educated 

 man who knew nothing of electricity and had never heard of a 

 telegraph or telephone, and if this man were assigned the duty 

 of making an investigation of the telegraph and telephone sys- 

 tems of a great city without any outside assistance whatever, 

 and of preparing a report upon all the physical equipment with 

 detailed maps of all stations and circuits and with an explana- 

 tion of the method of operation of every part, his task would be 

 simple compared with the problem of the neurologists. The 

 human cerebral cortex alone contains some 9280 million nerve- 

 cells, most of which are provided with long nerve-fibers which 

 stretch away for great distances and branch in different direc- 

 tions, thus connecting each cell with many different nerve- 

 centers. The total number of possible nervous pathways is, 

 therefore, inconceivably great. 



Fortunately for the neurologists, these interconnecting ner- 

 vous pathways do not run at random; but, just as the wires 



