The CNS is a soft, delicate tissue easily susceptible to damage. Nervous tissue proper, in the CNS, has little or no connective tissue. This is in contrast to the nerves and ganglia of the PNS, which possesses abundant connective tissue. The adult CNS exhibits little or no capacity for regeneration. Neurons cannot be replaced.
Glial cells can divide in response to damage, creating a glial scar.
The CNS is organized into White Matter and Grey Matter. The spinal cord has white matter on the outside and grey matter in the inside. All peripheral nerves contain Schwann cells that produce myelin for the myelinated axons and enclose and protect the unmyelinated axons. The nuclei one observes in nerves belong to Schwann cells. There are three levels of collagenous connective tissue within nerves.