Which region or regions of the central nervous system have an external layer of gray matter?

The cerebrum and cerebellum region

Explanation:

The central nervous system (CNS) is a system in the body that combines and coordinate information and activities in the entire body of an organism. On one hand, the CNS is generally made up of 2 structural components namely:

On another hand, the CNS can be divided into;

Structurally, the brain is divided into three regions:

Except for the brainstem whose gray matter is localized in a white matter embedded nuclei , the brain generally consists of an outer cortex of gray matter and an inner tracts of white matter.

Hence, the regions of the CNS with external layer of gray matter are the cerebrum and the cerebellum regions.