Another example of a synthesis reaction is the formation of sodium chloride (table salt). Because of the very high reactivities of sodium metal and chlorine gas, this reaction releases a tremendous amount of heat and light energy.
Schwann cells make myelin in the peripheral nervous system (PNS: nerves) and oligodendrocytes in the central nervous system (CNS: brain and spinal cord). In the PNS, one Schwann cell forms a single myelin sheath (Figure 1A).
Each oligodendrocyte can supply myelin for several axons and each axon can be supplied by several oligodendrocytes. Oligodendrocytes wrap the myelin around the axons in thin sheets like rolled up paper. Schwann cells, another kind of glial cell, makes a slightly different kind of myelin in the peripheral nervous system.When parts of the myelin sheath is lost, oligodendrocytes attempt to replace it. In acute MS lesions, typical of very aggressive disease courses, oligodendrocytes are found in large numbers and there is evidence of abortive remyelination-probably the new myelin is being destroyed faster than the oligodendrocytes can lay it down.