The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
Nerve fibers (axons) are often covered by a special insulating layer called the myelin sheath. This covering is composed of the membranes of specialized cells called oligodendrocytes (in the brain and spinal cord, or central nervous system) and Schwann cells (throughout the rest of the body). In axons throughout the body, the outermost sheath formed by the presence of Schwann cells wrapping around the axon is called the neurilemmal sheath. This neurilemmal sheath is composed of the nucleus and cytoplasm of the Schwann cells. It is thus also called the sheath of Schwann. Because axons in the central nervous system are not insulated by Schwann cells, they have no neurilemmal sheath.
The neurilemmal sheath plays an important role in the potential regeneration of injured axons throughout the body. When an axon is cut or seriously damaged, causing it to be detached from its nucleus or soma, the axon will degenerate. Specialized immune system cells will clean up the resulting debris. The neurilemmal sheath, now an empty tube, is left behind. If the soma is uninjured, it may be able to begin to sprout a new axon. This new sprout will find its way into the empty neurilemmal sheath. When full recovery is possible, Schwann cells will myelinate the new axon within the old neurilemmal sheath.