Invertebrate Myelin Web Page

[updated Jan-07]
"Glial cells surround the neurons of invertebrates ... but in a loose association that does not form true myelin"

                      F. Delcomyn: Foundations of Neurobiology W.H. Freeman 1998

... so why bother reading what follows?

Myelin

Myelin is a multilayered membranous ensheathment of axons. It speeds nerve impulse conduction, decreases metabolic costs of neural activity and decreases space requirements of the nervous system. These features have clear selective advantage. Myelin is best known and best characterized in vertebrates, where it is a key to subphylum success. Several serious diseases in humans are caused by pathologies involving myelin. Myelin is often considered to be an exclusively vertebrate innovation. However, functionally-equivalent ensheathments of axons have arisen apparently independently at least twice each in annelids and crustaceans (Schweigreiter et al 2006). For a detailed summary of the occurrence of myelin among invertebrates, click here . A list of references to the long scientific literature on invertebrate myelin follows:

Literature on invertebrate myelin

General reviews etc

Oligochaete myelin

Polychaete myelin

Copepod myelin

Malacostracan myelin (shrimp etc.)

Penaeid shrimp myelin

Caridean shrimp myelin

Myelin in other malacostraca

(* myelination not confirmed by electron microscopy)

More doubters ...

"Only vertebrate neurons have myelin sheaths"
				answers.com 11/10/06

"Invertebrates lack myelin on their axons."
				animalbehavioronline.com 11/12/06

"No invertebrate has myelin..."
				J. Kiernan Anatomical Foundations of Neuroscience web page 11/12/06

"Invertebrate glia do not generate myelin sheaths, and the Drosophila genome lacks orthologs of most myelin genes (Marc R. Freeman, unpublished)"  Freeman and Doherty (2006) TINS 29: 82-90 


This material has been assembled and presented as a public service by Dan Hartline, Bekesy Laboratory of Neurobiology, Pacific Biosciences Research Center, University of Hawaii at Manoa (danh at hawaii.edu). Opinions expressed here are those of the author and do not represent the positon or policies of the University or any funding agency.