The nerve fiber represents the mere continuation of the axon. From this viewpoint it should not be considered as a special element; but the structural details that it presents along its course until the terminal arborization are so special that justify the study of this important component of the nervous system in a separate chapter.
KeywordsMethylene Blue Nerve Fiber Myelin Sheath Silver Nitrate Myelinated Fiber
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- 1.These clefts have also been indicated by Schmidt (1874)Google Scholar
- 2.[Structure of the nerve cell, Chapter VI, page 134 and subseq.]Google Scholar
- 3.[Simarro (1900) has stained recently with his method, this first ring of cement in motor cells of the rabbit spinal cord.]Google Scholar
- 4.Dogiel (1896c) has drawn these nodes in the cerebellum of birds stained with methylene blue, and we have seen them perfectly stained with this dye in the spinal cord, cerebrum and cerebellum of mammals (Cajal, 1896e, f).Google Scholar
- 5.Many of these details are taken from our work: El azul de metileno en los centros nerviosos (Cajal, 1896f).Google Scholar
- 6.[Certain authors, Apathy for example, describe in invertebrates (Hirudo, Lumbricus, etc.) a special covering comparable to the myelin sheath. This, sometimes very substantial sheath does not have the chemical properties nor the structure of the myelin of vertebrates.]Google Scholar
- a.Fig. 89.—d, welding disc.Google Scholar
- b.It is well known by now that the cytoplasm of the Schwann cell, which is extruded from the tight wrapping of the myelin lamellae, accumulates in a) the outer ridge represented by Cajal’s protoplasm around the nucleus of the Schwann membrane; b) the inner ridge, embodied probably in what Cajal describes as the sheath of Mauthner; and c) the Schmidt-Lantermann clefts and paranodes [Peters, Palay, Webster (1976) The Fine Structure of the Nervous System. Saunders, Philadelphia, pp 194-200].Google Scholar
- c.The concept of myelin formation has changed indeed, the myelin being a derivative of Schwann cell membranes in peripheral exons with the corresponding nuclei of Schwann cells present [Geren (1954) Exp Cell Res 7: 58-562], and membranes of oligodendrocyte processes in central axons with no nuclei (Peters (1960) J Biophys Biochem Cytol 7: 121-126].Google Scholar
- d.The sheath of Retzius is known presently as the sheath of Henle. It is made of reticulin fibers, i.e. connective tissue components, which are continuous with the endoneurium [Peters, Palay, Webster (1976) The Fine Structure of the Nervous System. Saunders, Philadelphia, p 328].Google Scholar
- e.Fig. 94.—o, probably unmyelinated fiber.Google Scholar
- f.Cajal uses the term neurilemma for the epineurium. To day, neurilemma is another designation for the Schwann sheath. For discussion see: Young (1942) Physiol Rev 22: 318-374 (pp 321-322)Google Scholar