48o 



HANDBOOK OF PHYSIOLGG"!' 



NEUROPHYSIOLOGV 



rhizotomy. We are hence without positive evidence 

 that pain impulses in clinically significant numbers 

 transverse the anterior roots to enter the spinal cord in 

 man. 



P.MN .AND .AUTONOMIC NERVOUS SYSrE.VI 



This system of nerves was defined by Langley (155) 

 as efferent and distinguished from the somatic ner- 

 vous system by a peripheral synapse. He was will- 

 ing to regard as autonomic afferent fibers only "those 

 which give rise to reflexes in autonomic tissues and 

 which are incapable of directly giving rise to sensa- 

 tion." He considered all other afferent fibers somatic. 

 We have since his time become progressively more 

 aware that most of the nerves of gross anatomy named 

 "autonomic' contain pain fibers. This is true in vir- 

 tually all of the sympathetic and pelvic parasympa- 

 thetic nerves to the torso; the distribution of these 

 insofar as they are known has ijeen diagrammatized 

 by White [see figs. 127, 130, 131, 133 and 134 in 

 White & Sweet (296)]. Evidence for the presence of 

 pain fibers in these nerves has been gleaned both 

 upon stimulation and after denervation. These vis- 

 ceral pain fibers differ from autonomic efferents in 

 their probable nonstop course through the para- 

 vertebral ganglia to enter the posterior roots of the 

 spinal nerves. 



Sympathetic Nerves 



The concept that the efferent sympathetic path- 

 ways leave the cord only from the lowermost cervical 

 to the upper lumbar segments and enter the sym- 

 pathetic chain via the white rami communicantes is 

 so well-established that it has led to ready acceptance 

 of Langley's statements that the afferent fibers 

 travelling with the sympathetic nerves also return 

 impulses to the spinal cord only by way of these white 

 rami. Thus in one study (156) leading toward this 

 conclusion he deduced that sensory fibers of the cat's 

 major accelerator nerve, the chief sympathetic nerve 

 to the heart, entered the cord only by the top 5 white 

 rami. He found in general that stimulation of the 

 central ends of the gray rami produced "no observable 

 physiological effect" in cats (155). Largely by histo- 

 logic study of degenerating myelin after section of 

 various nerves he concluded that the cell bodies of the 

 afferent fibers travelling with the sympathetic nerves 

 are only in the posterior root ganglia of the nerves 

 with white rami. For example, upon section of the 



cervical sympathetic trunk below the superior cer- 

 vical ganglion he found complete degeneration of 

 the fibers rostral to the cut and extending up to the 

 ganglion C'SS)- This conclusion unfortunately rested 

 on the misconception that there are no nonmedullated 

 afferent fibers (i 54) which we now know to be wrong. 

 His histologic studies would have failed to demon- 

 strate degeneration in these. Ranson (218) reached 

 the same conclusions, again relying heavily on micro- 

 scopic studies of myelin degeneration. He said, 

 "Histologically it is possible to trace sensory fibers 

 through the sympathetic system because of their rela- 

 tively large size." These statements were all made 

 before the 'C fiber days of Gasser and Erlanger, 

 and the conclusions reached from them require modi- 

 fication not only because of that work but also be- 

 cause of later observations in man. 



To begin with the neck, we point first to Leriche 

 & Fontaine (168) who studied pain in 10 operations 

 on nine patients by faradic stimulation to the superior 

 cervical ganglion and to the rami communicantes 

 of the second and third cervical nerves. The pain 

 was referred mainly behind the ear and to all the 

 teeth in the lower jaw. Stimulus to the trunk just 

 below the ganglion caused pain of similar locus which 

 was often very intense and might even last several 

 days. Leriche (167) explained this on the basis of 

 stimulation of vasomotor fibers in the area of pain 

 rather than ascribing it to direct stimulation of af- 

 ferent fibers in the sympathetic nerves. Foerster et al. 

 (79, p. 147) likewise produced pain upon stimula- 

 tion of the cervical sympathetic trunk at every 

 operation thereon undertaken under local anesthe- 

 sia. The pain was referred somewhere to the ipsilat- 

 eral side of the neck or head. But they added the ob- 

 servation that stimulus to the caudal cut end of the 

 cervical sympathetic trunk likewise caused pain of 

 the same severity and distribution. From this they 

 concluded that the stimulus was indeed to afferent 

 fibers directly and that these were entering the spinal 

 cord lower down. Frazier's (82) results on stimulation 

 both to carotid vascular plexuses and superior 

 cervical ganglia were less consistent, but in three of 

 four patients upon stimulation at some point in the 

 above zones pain was described in the ipsilateral 

 head or neck. Peet (209) has also produced pain in 

 the trigeminal zone "in a number of patients" upon 

 electrical stimulation of the superior cervical ganglion. 



To determine the mechanism of this pain Davis 

 & Pollock (55) carried out a series of experiments in 

 cats. They found no evidence of pain on stimulation 

 of the intact cervical sympathetic trunk, and Langley 



