This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
Decreased protein: lipid ratio is seen in 
Select and explain. 
A. Inner mitochondrial membrane, B. Outer mitochondrial membrane, C. Sarcoplasmic reticulum, D. Myelin sheath membrane
D: Myelin sheath membrane
Answer: D: Myelin sheath membrane 
Explanation: 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