Prolonged individuality of the accessory contribution to the vagusA peculiarity of the pig.код для вставкиСкачать
Prolonged Individuality of the Accessory Contribution to the Vagus: A peculiarity of the pig A. H. SAFANIE Department o f Biological Structure, College of Veterinary Medicine, University of Illinois, Urbana, Illinois The bulbar and spinal components of the accessory nerve of the pig are thoroughly integrated i n a common trunk at the jugular foramen. The fibers of bulbar origin separate from this trunk to form the internal ramus. The latter is especially demonstrable in the pig, since it is independent over a considerable distance i n the upper part of the neck before joining the vagus. As f a r distally as the origin of the recurrent laryngeal nerve, the efferent fibers contributed to the vagus by the accessory nerve remain histologically separate from the afferent fibers belonging properly to the vagus. Parasympathetic, branchiomotor and afferent fibers can be distinguished in the vagal trunk without the necessity of inducing selective degeneration by supranodose vagotomy. ABSTRACT The accessory nerve, as customarily de- ('14), "No such thing as the internal scribed in mammals, originates by the branch of the accessory exists in the dog." union of bulbar and spinal roots and di- Similar observations have been made in vides almost immediately into internal and other mammals (Kiss, '32; DuBois and external rami. The internal ramus is con- Foley, '36; Holzmann and Dogiel, 'lo), intributed to the vagus, and constitutes a cluding man (van Gehuchten and Molhant, major portion, if not the entire, efferent '12). In the pig, the distance between the component of that nerve, distal to the origin of its pharyngeal branch (House and brain stem and the nodose ganglion is Pansky, '60). This terminology has often disproportionately long. The internal rabeen criticized on the grounds that the in- mus of the accessory nerve (actually the ternal and external rami actually represent motor root of the vagus) is atypically long unaltered continuations of the bulbar and and distinct, being anatomically separate spinal roots, respectively (Holl, 1878; from the vagus as far distad as the caudal Lesbrb: and Maignon, '07; Chase and Ran- pole of the ganglion (Lesbrt5 and Maignon, son, '14; Kiss, '32; DuBois and Foley, '36; '07; Kiss, '32; Holzmann and Dogiel, '10; Both et al., '37). Thus, there are two sep- Dogiel and Archangelsky, '06). The present arate fiber populations, originating from study was undertaken to determine the medulla and the spinal cord, whose whether this segregation of afferent and only basis for being Considered together is efferent components might be histologia transitory union at the jugular foramen. cally discernible at lower levels of the According to Holl (1878), Willis' original vagal trunk. With a view to subsequent description of the accessory nerve included quantitative studies, right and left vagi of only that portion which originates by the more than 50 randomly selected pigs were coalescence of spinal rootlets and termin- examined for evidence of component segates as the external ramus. The bulbar regation in closely spaced transverse secrootlets and internal ramus, originally de- tions. Some were prepared by the Wolters scribed as part of the vagus, were mis- method (Quilliam, '56) and others by routakenly identified with the accessory nerve tine histological procedures. through misinterpretation of Willis' paper OBSERVATIONS by Scarpa and others of his day. Throughout its course in the neck and The internal ramus usually loses its identity almost immediately through inte- upper thorax, the vagal trunk was regugration of its fibers with those of the vagus. larly subdivided into two contrasting zones Thus, as emphasized by Chase and Ranson (fig. l a ) whose architecture conformed ANAT. Rec., 159: 1 4 . 1 2 A . 11. SAFANIE closely with descriptions of segregated afferent and efferent fiber populations observed intracranially in other species (Chase and Ranson, '14; Botiir et al., '37; Heinbecker and O'Leary, ' 3 3 ) . The afferent bundles were traced proximally into the nodose ganglion, the efferents to the accessory nerve. The latter did not enter the ganglion but were loosely adherent to its lateral surface. Rostra1 to the ganglion, the two groups of fasciculi were grossly separate. As shown in figure l b , the bundles contributed by the accessory nerve consisted of closely packed myelinated fibers of two distinct sizes. The larger ones (8-12 11) peeled off en masse in the recurrent laryngeal nerve and were traced to the laryngeal muscles. The more numerous, small fibers (2-4 11) were accordingly identified as parasympathetic. The afferent bundles (fig. l c ) contained iiiyclinated fibers in a continuous range of thicknesses, some as large as 10 11; but the smallest ones predominated. Between them, in myelinstained sections, were relatively wide intervals of unstained tissue, in which could be seen the indistinct outlines of numerous unmyelinated fibers. A t the jugular foramen, the bulbar and spinal components of the accessory nerve Fig. 1 Vagus of pig as seen histologically at cervical and upper thoracic levels, Wolters myelin stain. a: efferent (left) and afferent (right) sectors are apposed along an oblique line ( X 29). b: efferent, and c, afferent fiber populations ( x 333). were thoroughly integrated in a common trunk, which contradicts the view that the two groups of fibers are related merely by loose intrathecal approximation (Holl, 1878; Chase and Itanson, '14; DuBois and Foley, '36). In figure 2, just proximal to the parting of the internal and external rami, the original segregation of bulbar and spinal fibers has been almost reestablished, but a degree of interchange between the two regrouping populations is still visible. The fibers of spinal origin, now constituting the external ramus, are uniformly large. In the internal ramus can be seen large and small fibers of bulbar origin, representing branchiornotor and parasympathetic components, destined for distribution in branches of the vagal trunk. As the intracranial trunk of the accessory nerve is independent of the vagus, it is probable that the only efferent fibers actually contained in the vagus at this level are those of its pharyngeal ramus. I~ISCUSSIOIK Segregation o l afferent and efferent vagal components in other mammals is apparently limited to the sorting of large, branchiomotor fibers into a peripheral zone of the lower cervical vagus, preparatory to their detachment in the recurrent laryngeal nerve (Chase and Ranson, '14; Botjr et al., '37; IIeinbecker and O'Leary, '33; Foley and DuBois, '37; Evans and Murray, '34; Agostoni et al., ' 5 7 ) . Insofar as I have been able to determine, no species has been described previously in which the Fig. 2 Accessory nerve dividing to form external (left) and internal (right) rami. Fibers of spinal (left) and bulbar (right) origin are intermixed at center. Hulbar component, now constituting the internal ramus, continues as the efferent component of the vagus. Wolters myelin stain ( x 92). ACCESSORY CONTRIBUTION T O VAGUS O F PIG accessory contribution of branchiomotor and parasympathetic fibers remains histologically distinct throughout the extent of the cervical and upper thoracic vagus. Previous quantitative studies of vagal components in other mammals have largely depended upon subtracting the number of fibers which survive supranodose vagotomy from the number normally present in the vagus (DuBois and Foley, ’36; Foley and DuBois, ’37; Evans and Murray, ’54; Agostoni et al., ’57). Because thc afferent and efferent components of the vagus of the pig arc histologically separate, their individual fiber populations can be analyzed and compared quantitatively in the same nerve trunk, without the necessity of inducing selective degeneration by vagotomy. LITERATURE CITED Agostoni, E., J. E. Chinnock, M. DeB. Daly and J. G. Murray 1957 Functional and histological studies of the vagus nerve and its branches to the heart, lungs and abdominal viscera in the cat. J. Physiol., 135: 182-205. BotPr, J., G. Popjak and A. Bense 1937 Die Fasern des Ncrvus vaguacessorius beim Menschen und bei Saugetieren. Cluj Transylv., Acta Mcd. Szeged., 8 (fasc. 2 ) : 93-229. Chase, M. R., and S. W. Ranson 1914 The structure of the roots, trunk and branches of the vagus nerve. J. Comp. Neur., 24: 31-60. Dogiel, J., and K. Archangclsky 1906 Der Bewegungshemmcnde und der motorische 3 Nevenappatat des Herzens. Arch. ges. Physiol., 113: 1-96. DuBois, F. S., and J. 0. Foley 1936 Expcrimental studies on the vagus and spinal accessory nerves in the oat. Anat. Rcc., 64: 285-307. Evans, D. H. L., and J. G. Murray 1954 Histological arid functional studies on the fiber composition of the vagus nerve of the rabbit. J. Anat., 88: 32G337. Foley, J. O., and F. S . DuBois 1937 Quantitative studies of the vagus nerve in the cat. I. The ratio of sensory to motor fibres. J. Comp. Neur., 67: 49-64. van Gehuchten, A., and M. Molhant 1912 Contribution a l’ctude anatomique de nerf pneumcgastrique chcz l’homme. Le Nevraxe, 13: 55-97. Heinbecker, P., and J. OLeary 1933 The mammalian vagus nerve. A functional and histological study. Am. J. Physiol., 106: 623-646. Holl, &‘I 1878 . Uebcr den Nervus Accessorius Willisii. Arch. f . Anat. u. Physiol, Anat. Abt., pp. 491-517. Holzmann, K., and J. Dogicl 1910 Uber die Lage und den Bau des Ganglion nodosum n. vagi hi einigen Saugetieren. Arch. f. Anat. u. Physiol., Anat. Abt., pp. 33-43. House, E. L., and B. Pansky 1960 A functional approach to neuronanatomy. Elakiston, New York. Kiss, F. 1932 Das Verhaltnis zwischen Vagus und Sympatheticus. Cluj Transylv., Acta Med. Szcged., 6: 129-150. Lesbre, F. X., and F. M’aignon 1907 Sur la part qui revient la branche anastomotique du spinal dans les proprietes physiologiques du pneumogastrique ou pneumospinal. J. de M6d. Vet. et de Zootech., pp, 212-227. Quilliam, T. A. 1956 Some characteristics of myelinated fibre populations. J. Anat., 90: 172187.