Controls the chemical environment around neurons in the cns

The answer is astrocytes.

Explanation:

Astrocytes are a type of glial cell, which play an important role within the central nervous system, since they are in charge of providing protection, nutrients and structure to the neuron.

These have a form which is reminiscent of a star and they are formed from the ectoderm. Their main functions include:

In summary, they control the chemical environment revolving around the neuron.