Complex functions such as thinking and feeling as well as regulation of homeostasis are attributable to different parts of the brain. The entire CNS is encased in bone. The brain is within the cranium , while the spinal cord runs within a canal through the vertebrae . CSF provides a special chemical environment for nervous tissue, as well as an additional buffer against physical damage. This feature is known as the blood-brain barrier .
Gray matter consists of nerve cell bodies, dendrites, and axons.
Neurons in gray matter organize either in layers, as in the cerebral cortex, or as clusters called nuclei . White matter consists mostly of axons, causing it to look white due to the myelin sheathing of the axons. In the early embryo, the CNS forms as a relatively uniform tube. Besides being a conduit for fibers running between the spinal cord and higher regions of the brain, it contains control centers for involuntary functions such as blood pressure, breathing, swallowing and vomiting. Just above the medulla are the pons and cerebellum .