Final answer:
The 18 carbon amino alcohol derivative present in all sphingomyelin is sphingosine, and when it is attached to a fatty acid, the compound is known as ceramide.
Step-by-step explanation:
All sphingomyelin has an 18 carbon amino alcohol derivative called sphingosine. When sphingosine is attached to a fatty acid, it is known as a ceramide. These combinations are crucial to the structure and function of cellular membranes. Sphingomyelins, which are a type of sphingolipid, additionally contain a phosphoric acid and choline unit, making them important constituents of the myelin sheath that insulates nerve cells.