996 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



ultimately dependent on whether the fibers are 

 myelinated or not. Data concerning; the resteneration 

 of the nonmeduUated fibers in the cervical sym- 

 pathetic trunk of the rat (206) speak against this view, 

 howev'er. 



The regeneration of the nonmeduUated pregan- 

 glionic fibers in the raljbit vagus has been found to be 

 largely dependent on the site of the lesion (137)- If 

 the abdominal vagi arc crushed, a delayed functional 

 recovery of the stomach is obtained i)ut, if the nerves 

 are crushed in the cervical region, function does not 

 return \\'ithin 600 days. This was found to be due to 

 a growth of the parasympathetic fibers into the re- 

 current laryngeal nerve, the fibers apparently being 

 'guided' along the meduUated fibers. The syncytial 

 character of the sheaths of the nonmeduUated fibers 

 was suggested to be the causal factor for this diverted 

 regeneration. Regeneration of vagal filjers to the heart 

 after high lesions of the xagus nerve in cat and rabbit 

 may take place, however (68). 



Only very incomplete data are available concern- 

 ing the regeneration of postganglionic fibers. Appar- 

 ently, a functional reco\ery is obtained with great 

 difficulty, if at all, when the fibers to the cat's fore- 

 limbs are cut in the grey rami (239, 414). The post- 

 ganglionic fibers from the superior cervical ganglia 

 regenerate and give at least partial return of func- 

 tion after a long period in the rabbit (416) but rela- 

 tively rapidly in the cat (301, 389). It is obvious that 

 the regenerative capacity may to a large degree be 

 invalidated by a severe axonal reaction if the lesions 

 are situated near the ceil bodies of the cut fibers, 

 which may lead to cell death (282, 288). 



When functional regeneration has set in, a stage of 

 overcompensation may develop manifested by such 

 signs as a large pupil, exophthalmos and constricted 

 vessels (56, 57, 286, 301). This phenomenon is prob- 

 ably a consequence of the denervation supersensitivity 



(389)- 



That denervated tissues may be reinnervated by 

 outgrowth from intact nerve fibers in the x-icinity is 

 well-known in the somatic svstem (cf. 125). Evidence 

 has been given for collateral regeneration of sudo- 

 motor fibers in the cat's paw (212) and of pregan- 

 glionic fibers in the cat's partially denervated stellate 

 and superior cervical ganglion (165, 324). 



Practically nothing is known about the maturation 

 process of regenerating autonomic nerve fibers. Func- 

 tional recov-ery in the cat's superior cervical ganglion 

 may take place at a stage when the regenerating fibers 

 have still not been myelinated (67) and may show an 

 impulse conduction \elocity as slow as C fibers (i68j. 



Heterogeneous Regeneration 



In a series of well-known experiments, Langley & 

 Anderson (9, 262, 264, 271, 272) showed that the 

 peripheral ner\e fibers could be divided into three 

 groups with regard to their ability to replace each 

 other: efferents from the spinal cord, postganglionic 

 fibers and afferents. After cross-union, any particular 

 nerve within each of the first two groups is able to 

 establish functional connection with the peripheral 

 part of another nerve belonging to the same group. 

 They found, however, one puzzling exception: the 

 ciliary preganglionic fibers were able to replace the 

 postganglionic in inner\ating tlie pupillary sphincter. 

 This existence of separate classes of nerves was logi- 

 cally explained when Dale (92) pointed out that the 

 nerves in the first group are cholinergic and in the 

 second adrenergic. As the postganglionic fibers to 

 the pupillary sphincter were found to be cholinergic, 

 this exception in the system of Langley and Anderson 

 only confirmed the view that the compatibility of 

 nerves when cross-united is determined by the chemi- 

 cal mediator. 



The observations of Langley and Anderson have 

 been amply verified. Heterogeneous regeneration 

 has been demonstrated to give functional connection 

 between various somatic motor nerves and the su- 

 perior cervical ganglion (16, 99, 100, iii, 443), 

 between parasympathetic preganglionic fibers in the 

 vagus and this ganglion (16, 97, 99, 100, 186, 206), 

 and between preganglionic sympathetic fibers and 

 somatic motor nerves (18, 206). Afferent fibers have 

 been claimed to provide functional innervation of 

 voluntary muscle (436), but careful experiments 

 have shown this not to be the case (187, 437). There 

 is evidence that parasympathetic fibers to the salivary 

 glands may be misdirected by nerve lesions and give 

 functional innervation of sweat glands (395). Thus, 

 there is considerable evidence supporting the view of 

 Dale. The ability of neurons to liberate a certain 

 chemical mediator by nerve impulses in themselves 

 nonspecific is thus a property inherent in specific 

 types of neurons. 



There are some results as yet unexplained, how- 

 ever. The sensory root fibers of the nodose ganglion 

 have been stated (loi, 102) to achieve synaptic con- 

 nections with the postganglionic neurons in the cat's 

 superior cervical ganglion. Another peculiarity, as 

 shown by Anderson (9), is that no functional con- 

 nection is established between the preganglionic 

 oculomotor ner\es and the pupillary sphincter since 

 stimulation of the nerves did not elicit any response. 



