Sphingomyelin is also present in all eukaryotic cell membranes, especially the plasma membrane, and is particularly concentrated in the nervous system because sphingomyelin is a major component of myelin, the fatty insulation wrapped around nerve cells by Schwann cells or oligodendrocytes. Multiple Sclerosis is a disease characterised by deterioration of the myelin sheath, leading to impairment of nervous conduction. nSMase (Neutral sphingomyelinase; Sphingomyelin phosphodiesterase 2) converts sphingomyelin to ceramide. Although widely expressed in all tissues examined, except the spleen, high enzymatic activity occurs only in the brain. Mice lacking Smpd2 and Smpd3 are completely devoid of neutral SMase activity.
