PART V 

 THE CENTRAL NERVOUS SYSTEM 



SECTION XIV 



THE FUNCTIONAL SIGNIFICANCE OF THE NERVOUS 



SYSTEM 



CHAPTER XLV 



THE STRUCTURAL ARRANGEMENT OF THE NERVOUS 



SYSTEM 



The Subdivisions of the Nervous System. — Topographically the 

 nervous system presents itself as a central mass, consisting of the cere- 

 brum, cerebellum, basal ganglia, medulla and spinal cord, and a 

 peripheral complex, formed by the cranial, spinal and sympathetic 

 nerves. The latter, of course, also embraces a multitude of ganglia 

 as well as different ramifications in the form of plexuses and end-plates. 

 For structural and functional reasons the nervous system is commonly 

 divided into a cerebrospinal system and a sympathetic or autonomic 

 system. The former embraces the cerebrum, cerebellum, basal 

 ganglia, medulla, spinal cord, and the cranial and spinal nerves, while 

 the latter includes the different sympathetic and parasympathetic 

 ganglia throughout the body and the nerves connecting these ganglia 

 with the cerebrospinal system. This division is based upon: 



(o) Anatomical grounds, in that the gross arrangement of the sympathetic sys- 

 tem is very different from that of the cerebrospinal, consisting as we shall see later, 

 of a chain of ganglia, which begins above with the superior and inferior cervical, 

 and the superior, middle and inferior thoracic, and ends below with the solar, 

 and the pelvic ganglia. In many places the fibers emerging from these stations, 

 ramify very extensively, and form complex networks, or plexuses. 



(6) Histological grounds, in that the sympathetic nerve fibers are non-medul- 

 lated and connect with cells-bodies possessing a very characteristic shape. 



(c) Chemical grounds, in that the mass of the sympathetic neurones seems to 

 be made up of neuroplasm which is somewhat different from that constituting the 

 cerebrospinal neurones. 



(d) Functional grounds, in that the life processes regulated by the sympathetic 

 system remain for the most part subconscious. For this reason, sympathetic 

 reactions are very largely non-volitional and reflex in their nature. 



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