PHYSIOLOGY OF THE PERIPHERAL 



NERVES. 



CLASSIFICATION OF NERVE-FIBERS ACCORDING TO 



FUNCTION. 



As the nerve-fibers when stimulated possess the property of con- 

 ducting impulses in both directions, their physiological activity is es- 

 sentially dependent upon their relation to their peripheral end-organ 

 and to their central connection. In this way the individual nerve is 

 distributed to a definite area, within which, under normal conditions, 

 its function is exercised in the uninjured body. This activity of the in- 

 dividual nerve, due to its anatomical arrangement and connections, is 

 designated its specific energy. 



I. CENTRIFUGAL NERVES. 



(a) Motor. The center consists of central or peripheral ganglia; the end- 

 organ is a muscle. 



1. Motor fibers of transversely striated muscles. 



2. The motor nerves of the heart. 



3. The motor nerves of unstriated muscle-fibers, for example of the intestine. 

 The peculiarities of the movement induced by these nerves has been discussed 

 in the section on the Physiology of the Movement of the Digestive Apparatus 

 (pp. 280 and 547). The vasomotor nerves are deserving of especial consideration 

 in this group. 



(6) Secretory. The center is a central or peripheral ganglion, the end-organ 

 the glandular cell. 



Examples are furnished by the salivary secretion, the secretion of sweat, etc. 



(c) Trophic. The as yet unknown end-organ is situated in the tissues them- 

 selves, whose normal metabolism, growth, and uninterrupted intact existence they 

 control. 



In some tissues a direct connection with nerves is known to exist that is 

 capable of influencing their nutritive processes. Anatomically or physiologically, 

 the connection of the nerves with corneal cells, with the pigment-cells of the 

 frog's skin, the connective-tissue corpuscles of the serous coat of the frog's stomach, 

 with the cells that surround the stomata of the lymph-spaces, is known. 



The statements which are to follow with reference to the trophic functions of 

 certain nerves should be consulted, particularly the influence of the trigeminus upon 

 the eye, upon the mucous membrane of the mouth and the nose, upon the face; 

 of the vagus upon the lungs ; of the motor nerves upon the muscles ; of the nerve- 

 centers upon the conservation of nerve-fibers, and of certain central organs upon 

 individual viscera. 



Furthermore, a- description will be given here of the influence of the division 

 of nerves upon the growth of bone. H. Nasse found that the bones after such 

 an operation exhibited a diminution in the absolute amount of all their individual 

 constituents, but, on the other hand, an increase of fat. After division of the 

 spermatic nerve, degeneration of the testicle has been observed; after destruction 

 of the secretory nerve, degeneration of the submaxillary gland; after division of 

 the related nerve, interference with the nutrition of the cock's comb; after division 

 of the second cervical nerve (in cats and rabbits), loss of hair from the ear; changes 

 in the skin of the frog after injury of the spinal ganglia; after division of the 

 cervical sympathetic (which is attended with hyperemia of the corresponding half 



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