Electron microscopy of peripheral nerve fibers
1955 Volume 27 Issue 4 Pages 179-191_3
Details
1955 Volume 27 Issue 4 Pages 179-191_3
1. Ultrathin sections and macerated preparations of the sciatic nerves of adult mice have been examined with the electron microscope. Sections were prepared with a modification of the thermal expansion sectioning technique. Several fixatives were employed, and, of these, osmic acid proved best in researching the submicroscopic structures in the nerve fibers.
2. Exceedingly thin axon fibrils about 110 to 170 Å in diameter were observed in the axons. They were predominantly oriented in the long axis of the fiber and were apparently anastomosing with one another to form a network. Endoplasmic reticulum, from 600 to 1000 Å in diameter, was also found scattered throughout the axoplasm. They appear as tubular fibrils. Elongated narrow mitochondria,0.2 to 0.35μ in width, were also found in the axoplasm. Neurofibrils in the conven- tional sense are to be regarded as artifact caused by fixatiou.
3. A thin membrane, axolemma membrane in the conventional sense, was observed at the border between myelinated lamellae and axoplasm.
4. The myelin sheath was composed of a characteristic laminated structure which was observed as alternating concentric dark and light lamellae in thin section preparations. This structure was identical with the flexible lamellar structure, isolated single or in piles, in the fragmented preparations. The periodicity in the lamellar structure was measured by means of shadow casts as being of 140 to 170Å, corresponding to a shortened period brought about by drying. Schmid t-L ante r. mann incisures were also observed.
5. The myelin sheath was covered with neurilemma sheath consisting of a granular membrane, in average thickness of 400 Å. Mainly longitudinally arranged collagen fibrils were attached to this membrane. Sc hwann cell cytoplasm seems to continue to the neurilemma membrane.
6. Truly non-myelinated axons have been seen in the peripheral nerves. The contents of their axoplasm were similar to those of the myelinated fibers. Several non-myelinated axons were enclosed in the cytoplasm of a single Sch w an n cell and its outer limiting membrane.
