For 10 points, name this white insulating sheath covering the axons of neurons.
Proteins found in this substance include one that is alternatively spliced from the transcript of the Golli gene, and a glycoprotein often referred to as its namesake "protein zero". Shiverer mice can't make this substance, which is deficient in a leukoÂ·dystrophy. The most common sphingoÂ·lipid is named for this substance and forms this substance when mixed with galactoÂ·cerebroÂ·sides and cholesterol. This mixture of 85-percent lipid and 15-percent protein has a (*)  dielectric constant of 8, which is very low for biological systems. Saltatory conduction relies on the fact that this material is absent at nodes of Ranvier  (ron-vee-AY) . Oligodendrocytes and Schwann cells make this substance, which is destroyed in patients with multiple sclerosis. For 10 points, name this white insulating sheath covering the axons of neurons.
Proteins found in this substance include one that is alternatively spliced from the transcript of the Golli gene, and a glycoprotein often referred to as its namesake "protein zero".
 myelin  sheath [or  sphingomyelin ] 