Mylieran (French for “myelin”) is a compound used to assess the purity of myelin preparations. This method works on the principle that pure myelin samples will have low concentrations of other subcellular fractions; hence it’s important to use techniques which detect them, such as proteins, lipids or enzymes which have markers specific for them.

Myelination drastically speeds up nerve impulse transmission along axons, known as action potentials. Myelinated axons allow more information to pass quickly between nerve cells than ever before. Myelination occurs by assembling special structures at nodes of Ranvier on an axon membrane such as sodium channels that generate action potentials and myelin sheath proteins like neurofascin 186 and bIV-spectrin that organize and maintain these channels at these nodes of Ranvier nodes of Ranvier.

The peripheral nervous system (PNS: nerves) comprises many Schwann cells, each producing its own myelin sheath to cover an individual axon. Each myelin sheath consists of tightly interlaced inner and outer leaflets called lamellae that repeat radially around the axon, providing 250 to 300 turns of myelin wraparound it depending on axon size.

Myelination in the central nervous system (CNS; brain and spinal cord) is performed by oligodendrocytes. Unlike in the PNS, one oligodendrocyte can myelinate multiple segments on multiple axons at once. CNS myelin has a spiral structure like PNS myelin but with no Schwann cell cytoplasm surrounding its glial tongue; instead it connects directly to plasma membrane of an oligodendrocyte.