Peripheral nerves consist of bundles of either myelinated or unmyelinated nerve fibers □ that are held together by connective tissue. This cross-section shows numerous fibers of a sciatic nerve U enclosed by the perineurium [2 (see Fig. 263). The perineurium is composed of very flat fibrocytes and collagen fibrils. Dense regular connective tissue covers the entire nerve.
1 Fascicle (nerve fiber bundle)
6 Adipose tissue
Stain: alum hematoxylin; magnification: x 10
Fiber bundle (fascicle) from the sciatic nerve (nervus ischiadicus). The perineurium H is a cover of connective tissue around the fascicles (here stained reddish brown). Connective tissue fibers extend from the perineurium into the fascicles where they form septa. The very delicate reticular fibers in the septa are called endoneurium. They weave around individual nerve fibers. Together with the Schwann cell plasmalemma, they constitute the endoneu-ral sheath. The endoneurium contains capillaries [3. Myelinated nerve fibers HI have different diameters. There are also groups of thin nerve fibers with little myelin sheathing O. The myelin sheath is rich in lipids and only slightly stained. The axons appear only as blue-violet dots. Schwann cells and fibro-cytes are not visible. Staining of nuclei was not done (cf. Figs. 262, 266-268). Fascicles (nerve fiber bundles) and the perineurium form the peripheral nerve. At its surface is a layer of dense regular connective tissue (epineurium) H. The epineurium seamlessly merges with the surrounding connective
^ 1 Perineurium
^ 2 Endoneurium
3 Blood vessel
01 4 Myelinated nerve fiber
2 5 Thin nerve fiber with little myelin sheathing 6 Epineurium
Stain: picro-blue black; magnification: x 200
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