This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
In Central nervous system the myelin sheath is formed by: 
Select and explain. 
A. Oligodendrocytes, B. Schwann cells, C. Microglia, D. Astrocytes
A: Oligodendrocytes
Answer: A: Oligodendrocytes 
Explanation: Ans. A. OligodendrogliocytesApart from neurons, CNS also contains glial cells known as neuroglia. Number of glial cells is five times that of neurons Schwann cells found in peripheral nervous system are also glial cells. In the CNS there are three types of glia:MICROGLIA Scavenger cells which enter the CNS from blood vessels OLIGODENDROCYTES Involved in myelin formationASTROCYTES Produce substances that are trophic to neurons but their exact role is not known