<prompt> Decreased protein: lipid ratio is seen inInner mitochondrial membraneOuter mitochondrial membraneSarcoplasmic reticulumMyelin sheath membrane  <response>: Myelin sheath- The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and facilitates the transmission of nerve impulses. In the peripheral nervous system, the sheath is formed from the membrane of the Schwann cell, and the central nervous system it is formed from oligodendrocytes.Ref: Ganong;s review of medical physiology: 24th edition 