FIBER NUMBERS AND SIZES IN INFERIOR ALVEOLAR NERVE OF CAT

Abstract

Previous studies with the light microscope (LM) of paraffin-embedded, metal-impregnated sections have probably underestimated the narrow fiber components of the inferior alveolar nerve in the cat. In this study the inferior alveolar nerve of a young adult cat was fixed in situ with glutaraldehyde, post-fixed in osmium and embedded in plastic. A 1 .mu.m section of the whole nerve, and an ultrathin section of its largest bundle were cut. Montage micrographs were made from both sections, and from tracings the number and size distribution of the nerve fibers were measured. The entire nerve contained 6856 myelinated nerves whose diameters were distributed bimodally with peaks at 3-4 and 9-10 .mu.m. This total is higher than all previously published counts of this nerve, the increase being due to the detection of a greater number of narrower myelinated fibers. In the bundle examined by EM, 51.4% of the fibers counted were non-myelinated, 4 times as many as found in previous studies. The number and distribution of myelinated fibers found by EM was very similar to that found by LM. The size distribution of myelinated nerves was similar in all the bundles examined. Apart from a lower incidence of non-myelinated fibers, the population of the core of the larger bundle was similar to that of the periphery.