Slide #DMS 095 [Myelinated nerves, Osmicated]. Study a transverse section of a small nerve trunk stained with osmic acid. The funicular (bundled) arrangement of nerve fibers is evident and the connective tissue sheaths can be recognized although they are not stained. The osmic acid blackens the myelin sheaths. Identify large, medium, and small myelinated fibers. Some non-myelinated fibers are also present but are difficult to discern in this preparation.
This is very low power view of a cross-section through a peripheral nerve trunk stained with osmic acid which blackens the myelin sheaths. A bit of the epineurium grouping the five fascicles together may be seen around the periphery of the nerve, and each fascicle is seen to be enclosed by a layer of perineurium.
At this still low power, one may now easily define the perineurium, the connective tissue sheath that groups nerve fibers (axons) together into fascicles. The individual myelinated axons are also easily resolved at this power.
This medium power image through a portion of a single nerve fascicle shows well the individual myelinated axons (stained black by the osmium stain) and some of the endoneurium, the thin layer of connective tissue (stained brownish) that surrounds each nerve fiber. The perineurium delimits the fascicle itself.