248 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



Autonomic Nervous System. — According to Langley, the 

 efferent fibers from the nerve cells of the sympathetic and related 



PreQuno h on'ieji ore. 



Fig 110.— Schema to show the general relation between 

 the preganglionic and postganglionic fibers of the autonomic 

 patb^. 



gangUa supply the plain muscle tissues, the 

 cardiac muscles, and the glands, — that is, the 

 organs of the involuntary or, according to an 

 old nomenclature, the vegetative processes of 

 the body. He proposes for this entire system 

 of efferent fibers the term "autonomic," to indi- 

 cate that they possess a certain independence 

 of the central nervous system. The autonomic 

 path consists of two neurons: one belonging to 

 the central nervous system, whose axon emerges 

 in one of the spinal or cranial nerves and ends 

 around the dendrites of a sympathetic cell ; and 

 one occurring in some one of the numerous 

 sympathetic ganglia, whose axon passes to the 

 peripheral tissue. The first axon is spoken of as 

 the preganglionic fiber, the second as the post- 

 ganglionic fiber. Their connections are repre- 

 sented in the accompanying schema (Fig. 110). 

 Physiological and anatomical investigations 

 have shown that autonomic nerve-fibers arise 

 from four regions in the central nervous system 

 (Fig. Ill): First, from the midbrain, emerging 

 in the third cranial nerve and passing via the 

 cihary ganglion; second, from the bulbar region, 

 emerging in the seventh, ninth, and tenth 

 cranial nerves; third, from the thoracic spinal 

 nerves (first thoracic to fourth or fifth lumbar) 

 and passing in general via the ganglia of the 

 sympathetic chain; fourth, from the sacral 

 region by way of the so-called nervus erigens 

 supplying the descending colon, rectum, anus, 

 and genital organs. The autonomic fibers at 



Fig. 111.— lUus- 

 trating the central ori- 

 gin of the autonomic 

 fibers. — (,Langley.) 



