Physiology of the Peripheral Nerves. 



342. FUNCTIONAL CLASSIFICATION OF NERVE-FIBRES. As nerve- 

 fibres, on being stimulated, are capable of conducting impulses in both directions 

 ( 338), it is obvious that the physiological position of a nerve-fibre must depend 

 essentially upon its relations to the peripheral end-organ on the one hand, and its 

 central connection on the other. Thus, each nerve is distributed to a special area 

 within which, under normal circumstances, in the intact body, it performs its 

 functions. This function of the individual nerves, determined by their anatomical 

 connections, is called their "specific energy." 



I. Centrifugal or Efferent Nerves. (a) Motor. Those nerve-fibres whose 

 peripheral end-organ consists of a muscle, the central ends of the fibres being 

 connected with nerve-cells : 



1. Motor fibres of striped muscle ( 292 to 320). 



2. Motor nerves of the heart ( 57). 



3. Motor nerves of smooth muscle, e.g., the intestine ( 171). The vaso-motor nerves are 

 specially treated of in 371. 



(b) Secretory. Those nerve-fibres whose peripheral end-organ consists of a 

 secretory cell, the central ends of the fibres being connected with nerve-cells. 



Examples of secretory nerves are the secretory nerves for saliva ( 145) and those for sweating 

 (289, II.). It is to be remembered, however, that these fibres not unfrequently lie in the 

 same sheath with other nerve-fibres, so that stimulation of a nerve may give rise to several 

 results, according to the kind of nerve-fibres present in the nerve. Thus, the secretory and 

 vaso-motor nerves of glands may be excited simultaneously. 



(c) Trophic. The end-organs of these nerve-fibres lie in the tissues themselves, 

 and are as yet unknown. These nerves are called trophic, because they are 

 supposed to govern or control the normal metabolism of the tissues. 



In some tissues, we know of a direct connection of their elements with nerve-fibres, which 

 may influence their nutrition. Nerves are connected with the corneal corpuscles ( 201, 7), 

 with the pigment-cells of the frog's skin {Ehrmann), the connective-tissue corpuscles of the 

 serous membrane of the stomach of the frog, and the cells around the stomata of lymphatic 

 surfaces ( 196, 5) (E. F. Hoffmann). 



Trophic Influence of Nerves. The trophic functions of certain nerves are referred to as 

 under : On the influence of the trigeminus on the eye, the mucous membrane of the mouth 

 and nose, the face ( 347) ; the influence of the vagus on the lungs ( 352) ; motor nerves on 

 muscle ( 307) ; nerve-centres on nerve-fibres ( 325, 4) ; certain central organs upon certain 

 viscera ( 379). 



Section of certain nerves influences the growth of the bones. H. Nasse found that, after 

 section of their nerves, the bones showed an absolute diminution of all their individual con- 

 stituents, while there was an increase of the fat. Section of the spermatic nerve is followed by 

 degeneration of the testicle (Nelaton, Obolensky). After extirpation of their secretory nerves, 

 there is degeneration of the sub-maxillary glands (p. 213). Section of the nerves of the cock's- 

 comb interferes with the nutrition of that organ (Legros, Schiff). After section of the 2nd 

 cervical nerve in rabbits and cats, the hair falls off the ear on that side {Joseph). Section of the 



