biology lesson

July 30, 2007 at 7:56 pm

Hi all,

I have a pdf document that I saved a long time ago – I don’t have any idea where I found it, but I’d be glad to share it with anyone that is interested. It is titled:

Chapter 1 Literature Review

First, a little info about myelin:

Section 1.1 Components and structure of peripheral nerve

Peripheral nerve myelin (PNM) is a greatly extended and modified plasma
membrane wrapped around the nerve axon in a spiral fashion which originates from
and is a part of the SC. Each myelin-generating SC furnishes myelin for only one
segment of any given axon. The periodic interruptions where short portions of the
axon are left uncovered by myelin are the nodes of Ranvier.

My understanding of the descriptions of myelin is that it is a part (extension) of the schwaan cell. It seems like there is a different schwaan cell for each predetermined portion of the nerve. Somewhere I read that if the schwaan cell dies, then that section of nerves will not be remyelinated, otherwise, as long as the schwaan cell is functionally intact, then it can repair the damage caused by cytokines & anti-bodies. Myelin is composed of layers of lipids (76%) & proteins.
Glycolipids found in infectious agents are similar to the the glycolipid composition of myelin.

For those of you who have anti-bodies against MAG (myelin associated glycoprotein):

MAG is a transmembrane glycoprotein and a member of the immunoglobulin (Ig) supergene family. . . . MAG is not essential for myelination. . . . . .in the PNS it is essential for the signaling from SCs to axons that is needed for the normal maintenance of myelinated axons

Here, a little about the Axons:

Axons, the unique extensions from the neuronal cell body, are long cellular processes that make up the nerve . . . .The length of axons varies, ranging from a few millimeters to about a meter in human . . . . three types of peripheral nerve fibers can be distinguished: somatic motor fibers, somatic sensory fibers and autonomic fibers. neurons are formed into bundles
by connective tissue . . . between axons as the endoneurium, as the wrapping around
bundles of fibers – the perineurium, and surrounds the entire nerve as the epineurium. Nerves are
richly supplied by intraneural blood vessels

Axons that have been damaged can be repaired as long as the cell body has not died – it is a long, slow process as I know most of your are familiar with. In axonal damage, the cytokines &/or anti-bodies are sometimes “delivered” by way of intraneural blood vessels – in these types of injuries the myelin can be left intact. Not all damage starts at the myelin. Another point of entry on the nerves involves the exposed areas of the nerves at the Nodes of Ranvier where a gap exists in the myelin.

Well, that’s the end of this brief biology lesson (just kidding). The entire document is 192 pages – quite a lot of detailed info for those brave enough to wade through it. Hope it provided some answers. Let me know if any of you want to take a gander at it.