Description of
Schwann Cells provided by Inner Learning Online. Larger axons passing through
Peripheral nerves commonly are enclosed in sheaths called "Schwann cells." These are tightly wound around the axons, somewhat like insulation on a wire. The smallest axons also are enclosed in Schwann cells, but they are not wound around the axons. These membranes are composed largely of lipid-protein that has a higher proportion of lipid (fat) than other cell surface membranes. This lipid-protein is called
Myelin, and it forms a "myelin sheath" on the outside of an
Axon. Axons that have myelin sheaths are called "myelinated" (or medullated) nerve fibers, while those that lack these sheaths are "unmyelinated" nerve fibers. Myelin serves as an insulator by preventing almost all flow of ions through the membrane. Considering this, it might seem that the myelin sheath would prevent the conduction of a
Nerve Impulse altogether, and this would be true if the sheath were continuous. It is, however, interrupted by some constrictions called "nodes of Ranier," which occur between adjoining Schwann cells. At these nodes, the fiber membrane is especially permeable to sodium and potassium ions.
Example of Research utilizing Schwann cells:One of the most exciting and promising therapies came recently from a research facility called, "The Miami Project" at www.themiamiproject.org/news.asp. This news was so exciting that I have included the complete text taken directly from the above referenced web-site:
"Combination Strategy Promotes Better Recovery of Walking
Investigators at The Miami Project have designed a new triple combination strategy that opens up new possibilities in the search for successful treatments for spinal cord injury. Damien D. Pearse, Ph.D., working with Mary Bartlett Bunge, Ph.D. and colleagues, tested their new strategy and found the treated animals improved to 70% of normal walking function. The new treatment combines Schwann cell grafts with the administration of rolipram and a form of cyclic AMP, drugs that influence axon growth.
Previous studies pioneered at The Miami Project have shown that Schwann cell transplants by themselves support
Regeneration in experimental spinal cord injury. What these earlier studies with Schwann cell grafts did not do is promote axons to leave the grafts and extend beyond the site of injury.
Researchers have learned that a reason the fibers do not re-enter the spinal cord beyond Schwann cell grafts is likely because of an inhibitory
Environment that exists within the spinal cord. These observations led Pearse and Bunge to consider a combination strategy to help damaged neurons overcome inhibitory signals after injury.
Research colleague Marie Filbin, Ph.D. of Hunter College, New York, recently demonstrated that cyclic adenosine monophosphate (cAMP), a messenger molecule that influences the inner workings of cells, is important for growth of axons across inhibitory environments. Interested in knowing what happens to cAMP after injury, Pearse and Bunge’s team determined the levels of cAMP in the brain and spinal cord following a contusion injury. They found that the levels of cAMP drop well below normal within one day of injury.
