Movie S3.

Structural remodeling of myelin by detachment of paranodal loops. Animation showing detachment of paranodal loops from the axon and withdrawal into the oligodendrocyte, increasing nodal gap length and thinning the myelin sheath. Note that the paranodal loop that borders the nodal gap is formed from the outermost layer of myelin, which is continuous with the plasma membrane of the oligodendrocyte through a slender process (the outer mesaxon or outer cytoplasmic tongue). During myelination, the length of the internode increases and additional layers of myelin are wrapped around the axon beneath the overlaying compacted sheath; thus myelin is a membrane system in which the layers can expand and contract and the layers slip over each other during myelin formation and remodeling. Accompanies Fig. 2.