Glial scar formation (gliosis) is a reactive cellular process involving astrogliosis that occurs after injury to the Central Nervous System. As with scarring in other organs and tissues, the glial scar is the body's mechanism to protect and begin the healing process in the nervous system. Although the glial scar does a good job at controlling and suppressing further physical damage, it does have important caveats to neuroregeneration. Particularly, many neuro-developmental inhibitor molecules are secreted by the cells within the scar that prevent complete physical and functional recovery of the central nervous system.
As an example, consider paralysis. After the physical injury that severs or damages the spinal cord, the formation of the glial scar partly explains why the patient is not able to fully recover functional normalcy.
Scar advantages
The ultimate function of the glial scar is to reestablish the physical and chemical integrity of the Central Nervous System. This is done by generating a barrier across the injured area that seals the nervous / non-nervous tissue boundary. This also allows for the regeneration of the selective barrier to prevent further microbial infections and spread of cellular damage. Moreover, the glial scar stimulates revascularization of blood capillaries to increase the nutritional, trophic, and metabolic support of the nervous tissue. [1]
Scar disadvantages
The glial scar unfortunately also prevents neuronal axon extensions. The central nervous system neuron's axons begin to sprout and extend across the injury site in an attempt to repair the damage. However, the scar prevents these extensions via physical and chemical means. Astrocytes are able to form a dense network of gap junctions that generates a physical barrier to axon extensions. Further, the astrocytes secrete several growth-inhibitory molecules that chemically prevent axonal extensions. Moreover, the basal membrane component is expected to generate an additional physical and chemical barrier to axonal extensions. [1]
http://en.wikipedia.org/wiki/Glial_scar