Describe the differences in structure between the sheathing cells of axons in the central nervous system and those of axons in rest of the body. What are the common functions that these sheathing cells perform?
In the central nervous system, the length of an axon is often enveloped by oligodendritic, specialized glial cells that wrap around the axon, from a point just after the axon arises from the cell body to the point at which the axon branches, forming a heavily-lipid myelin sheath. Outside the central nervous system, Schwann cells form the myelin sheaths around axons. The sheaths are interrupted at regular intervals by gaps, called the nodes of Ranvier, where one sheath cell stops and another one begins. The sheaths function to speed up the conduction of impulses along axons. Bundles of nerve cells bound together by connective tissue constitute a nerve. Packed together for structural convenience, each nerve cell is insulated from all others by its sheath and conducts its impulses separately from the impulses in other cells.
