Myelin sheaths surround nerve cell axons and are essential for proper nervous system function. They act as an electrically insulating layer and enable better propagation of action potentials. Sphingomyelin is a type of sphingolipid found in the myelin sheaths of animal cell membranes.

Lysosomal storage diseases occur when mutations cause defects in sphingolipid degradation enzymes. Simply put, the key word is "degradation," which indicates the presence of a disease. No other answer choice has a key word that indicates the presence of a disease.

Glucosamine contributes to the structure of glycosylphosphatidylinositol (GPI). Ceramide is the precursor to sphingomyelin, sphingosine is hydrolyzed to form ceramide.

All four of these sphingolipids differ only in the functional groups attached to the sphingosine. Ceramide has a fatty acid group; cerebroside has a monosaccharide group; ganglioside has a polysaccharide group; sphingomyelin has a phosphatidylcholine or phosphoethanolamine group. In terms of molecular mass, phosphatyidylcholine or phosphoethanolamine are the smallest as well as the least massive functional group, making sphingomyelin the sphingolipid with the smallest molecular mass.

Ceramide is formed by sphingosine. Sphingosine is formed by a long chain of sphingolipids. Both sphingomyelin and glycosphingolipids are formed from ceramide.