The numbers of nerve fibers in the vagus nerve of man

Abstract

In an earlier publication (Schnitzlein, Rowe and Hoffman, '58) counts were reported of the myelinated nerve fibers in the mid-cervical vagus, recurrent laryngeal nerve and esophageal plexus of autopsy specimens of man. Although these numbers probably include most of the motor component of the vagus nerve, the number of non-myelinated nerve fibers, many of which arise in the nodose ganglion (Foley, '37), could not be determined from these preparations.Segments of nerves adjacent to those previously reported in the myelinated fiber study have been impregnated with pyridine silver to determine the numbers and percentage of non-myelinated nerve fibers in these preparations. Such estimations have been reported on the cat (Jones, '32; Du-Bois and Foley, '36, '37; Foley and Du-Bois, '33, '34, '37; Hoffman and Kuntz, '57) but the available literature regarding the vagus nerve of man does not include comparable data.It is the purpose of this study to compare the total number of axons in the vagus nerve with the counts of myelinated nerve fibers previously reported and to observe, in so far as possible, the distribution of the non-myelinated nerve fibers. MATERIALS AND METHODSSegments of mid-cervical vagi, recurrent laryngeal nerves after all the grossly observable thoracic branches have been given off, and the esophageal vagi at the diaphragm were removed at 17 autopsies. The nerves reported in this study are adjacent segments just proximal to those reported in an earlier publication (Schnitzlein, Rowe and Hoffman, '58). The same limitations which applied to the removal of the nerve segments utilized in the mye-h a t e d study applies to those reported in this investigation.The counts reported here were made following a pyridine-silver impregnation technique in the course of which they were gold toned and counterstained with Feulgen, fast green and orange G (Foley, '38). An ocular-grid estimation technique ( Schnitzlein and Foley, '57) was used to enumerate the fibers. The microscopes employed were equipped with oil-immersion objectives (120 X, N. A. 1.3) and 15 X oculars in order to obtain adequate resolution and magnification. Nearly all reported counts represent an average of at least two independent estimations. It should be noted that some sympathetic fascicles may possibly course with the vagus nerve at all levels. These fascicles are usually readily recognizable, especially at mid-cervical levels in the pyridine-silver preparations, and have been eliminated as far as possible from the counts.Comparable levels of the vagus nerve were obtained from Rhesus monkeys and cats. These were utilized for a electron microscopic study, particularly of the small non-myelinated "Remak bundles" (Gasser, '50). OBSERVATIONS Mid-cervical vagusThe total number of nerve fibers in the mid-cervical vagus nerve of man (table 1 ) varies from 45,110 to 153,123 fibers (right av. I= 105,375 3-6281; left av. = 87,379 -C 3948). In most instances the highest counts were recorded in the right vagus nerve but great variation exists in different i...

Repeated assessment of larynx compound muscle action potentials using a self-sizing cuff electrode around the vagus nerve in experimental rats

“…Moreover, the proportion of myelinated axons in the 0165-0270/$ -see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2011.04.007 cervical left vagus nerve of rats is comparable to humans (Hofmann and Schitzlein, 1961;Soltanpour and Santer, 1996). At last, the left superior laryngeal nerve splits from the vagus nerve identically in rats and humans, as it runs back superiorly behind the aortic arch in a groove between oesophagus and trachea to finally enter into the larynx (Berthoud and Neuhuber, 2000;Paxinos, 2004).…”

Heart function influenced by selective mid-cervical left vagus nerve stimulation in a human case study

“…[4][5][6] Vagus nerve stimulation for cardiac control generally requires B-fiber stimulation; stimulation of A-and C-fibers is to be avoided. A published model study 7 proposes current charge-balanced stimulus trains with a quasi-trapezoidal cathodic phase with a leading edge i c D1 mA, a plateau t c ¼300 ms, an exponentially decaying phase t exp ¼500 ms and an anodic phase t a of magnitude i a D0.1Âi c (Figure 1b).…”

Frequency dependent effect of selective biphasic left vagus nerve stimulation on heart rate and arterial pressure

“…A and B-fibres, are primarily cardiovascular and respiratory neurons. (16)(17)(18)(19) Different types of nerve fibres respond differently to various types of stimulating pulses. (8)(9)(10)(11) To stimulate mostly B-fibres, the combination of quasitrapezoidal cathodic and rectangular anodic current pulses, which we used in our study, was previously proposed.…”