Updated 2015-07-26

Myelin is a multilayered membranous ensheathment of axons of the nervous system that greatly speeds conduction of nerve impulses. Its presence in nearly all vertebrate nervous systems reflects its multiple advantages. Best known and best characterized in vertebrates, where it is a key to subphylum success, it has arisen independently in at least three other (invertebrate) taxa: oligochaetes (earthworms), shrimp, and copepods (tiny planktonic crustaceans). The molecules, mechanisms and selective forces underlying this remarkable case of convergent evolution make a fascinating study. These pages attempt to outline what is known about myelin, its antecedents and its evolution and provide links to relevant sources and resources. [Please report factual erors, broken links, etc to Dan Hartline (danh at].

This information is presented in three, somewhat overlapping, categories: