Explain the differences in axon regeneration in the CNS and PNS, and the implica

Schwann cells, present in the PNS but not the CNS, facilitate regrowth of severed axons. This means that people do not recover as well from CNS injury compared to PNS injury. It is possible that there is something fundamentally different in CNS axons compared to PNS axons that accounts for this effect. To test for this, Schwann cells could be transplanted into the spinal cord or brain and CNS axons observed for regrowth. Such experiments have been done, and it is the case that CNS axons are capable of regrowth in the presence of Schwann cells. Identification of chemical or physical factors in the Schwann cells would advance this field of research.