5 2 4 TEXT-Bf)OK OF PHYSIOLOGY 



The spinal nerves, thirty-one in number on each side, are in anatomic 

 relation with the spinal cord, and because of the fact that they pass through 

 foramina in the walls of the spinal column they are termed spinal nerves. 

 As both cranial and spinal nerves are ultimately distributed to the structures 

 of the body i.e., the general periphery they collectively constitute the 



peripheral organs of the nerve system. 



The spinal nerves consist of two groups of nerve- 

 "fibers, a ventral and a dorsal group. Though 

 closely intermingled in the common trunk of the 

 spinal nerve they are distinctly separated near the 

 spinal cord. Owing to their connection with the 

 ventral and dorsal surfaces of the spinal cord they 

 have been termed respectively the ventral and dor- 

 sal roots. Peripherally the ventral root fibers are 

 distributed to skeletal muscles, glands, walls of 

 blood-vessels and walls of various viscera: the dor- 

 sal root fibers are distributed to skin, mucous mem- 

 branes, muscles, joints, etc. 



The central organs of the nerve system are sup- 

 ported and protected by three membranes named, 

 in their order from without inward, the dura mater, 

 the arachnoid, and the pia mater. 



The Encephalo-spinal Fluid. The general 

 subarachnoid space, as well as certain cavities within 

 the encephalon, contain a clear transparent fluid, 

 termed the encephalo-spinal fluid. This fluid has 

 an alkaline reaction and a specific gravity of 1.007 

 or 1.008. It is composed of water, proteins (pro- 

 teoses and serum globulin), and pyrocatechin 

 C 6 H 4 (OH) 2 , capable of reducing copper salts, 

 though not exhibiting any other of the properties 

 of sugar. In many respects this fluid resembles 

 lymph. The subarachnoid space and the general 

 encephalic cavities, termed ventricles, communicate 

 with one another by an opening in the pia mater 

 (the foramen of Magendie) as it passes over the 

 lower part of the fourth ventricle. 



The Functions of the Nerve System. It will 

 be recalled that the entire nerve system can be re- 

 solved into simple morphologic units, termed neu- 

 rones, each of which possesses certain histologic fea- 

 tures and physiologic properties; that their relation 

 one to the other both in a serial and collateral man- 

 ner gives rise to the general architecture of the nerve 

 system. Recalling the functions of neurons in their 

 individual and collective capacities the functions of the nerve system may be 

 formulated. 



The functions of the nerve system are twofold: (i) It unites and asso- 

 ciates the organs and tissues of the body in such a manner that they are 

 enabled to cooperate for the accomplishment of a definite object. (2) It 



FIG. 226. THE CENTRAL 

 ORGANS OF THE NERVE 

 SYSTEM. F. T. o. Frontal, 

 temporal, and occipital 

 lobes of the cerebrum. C. 

 Cerebellum, p. Pons. mo. 

 . Medulla oblongata. ms. y 

 ms. The upper and lower 

 limits of the spinal cord. 

 The remaining letters in- 

 dicate the region and num- 

 ber of the spinal nerves. 

 (Quain, after Bourgery.} 



