Ans. d. Lack of myelin inhibiting substance(Ref GanonGr 90; Clinical Box 4-)Following CNS injuries several events which provide inappropriate environment for regeneration are: (Ganong 23/e p90) Astrocytic proliferation)Activation of microgliaScar formationInflammationInvasion of immune cellsCNS neurons do not have the growth promoting chemical needed for the regenerationCNS myelin is a potent inhibitor of axonal growthAxon Regeneration in CNSThe proximal stump of a damaged axon in the CNS will form sho sprouts, but distant stump recovery is rare, and the damaged axons are unlikely to form new synapses. This is because:CNS neurons do not have the growth promoting chemical needed for the regenerationCNS myelin is a potent inhibitor of axonal growth.That is why treatment of brain and spinal cord injuries frequently focuses on rehabilitation rather than reversing the nerve damage. Following CNS injuries, several events which provide inappropriate environment for regeneration are:Astrocytic proliferationActivation of microgliaformationInflammationInvasion of immune cellsNew research is aiming to identify ways to initiate and maintain axonal growth, to direct regenerating axons to reconnect with their target neurons and to reconstitute original neuronal circuit.