Electron microscopic nerve fiber caliber analysis in the nerve branch to the venter rostralis of the M. digastricus in mice

Abstract

Nerve fiber counts and caliber analysis were performed with an electron microscope on 5 nerve branches to the venter rostralis of m. digastricus (VRD) from 3 mice. Branches contained an average of 42.4 (79.4%) myelinated fibers and 11.0 (20.6%) unmyelinated fibers. 68.4% of the sheaths of the myelinated fibers in the nerve branches were 6.5-8.5 microns (peak 7.0-7.5 microns) in major diameter and 76.4% were 5.0-7.5 microns (peak 6.0-6.5 microns) in minor diameter, 68.8% of the axons of the myelinated fibers were 4.5-6.5 microns (peak 5.5-6.5 microns) in major diameter and 76% were 3.5-5.5 microns (peak 4.0-5.0 microns) in minor diameter. The frequency distribution of the diameters showed that the nerve branch to VRD consisted of extra large myelinated fibers as in the r. digastricus to the venter caudalis of m. digastricus (VCD). Average ratios of the areas of the myelin sheaths to those of axons of the myelinated fiber transverse sections in the various axon area classes of the nerve branches were 0.7-2.9, and those ratios tended to decrease in the larger axon classes.