myelination (n.), myelinated (adj.)

https://doi.org/10.1351/goldbook.10985
The acquisition, development, or formation of a myelin sheath around a nerve fiber.
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 782 [Terms] [Paper]