In vertebrates, the brain lodges inside the skull and the spinal cord, inside a canal in the spine.
The brain and spinal cord are formed by glial cells, neuron cell bodies, and dendrite and axon bundles.
White and gray substance
The outermost layer of the brain is gray in color and is mainly formed by cell bodies of neurons. The innermost brain region is white in color and consists mainly of nerve fibers (dendrites and axons). The white color is due to the myelin sheath that lines the fibers.
In the spinal cord, the disposition of the gray and white substances is inverted in relation to the brain: the gray layer is internal and the white, external.
Both the brain and spinal cord are protected by three layers of connective tissue, generically called meninges. The thicker external meninge is the Dura mater; the median meninges is the arachnoid; and the innermost one is sink, firmly attached to the brain and spinal cord. The pia mater contains blood vessels, which are responsible for the nutrition and oxygenation of central nervous system cells.
Between the arachnoid membranes and pia mater there is a space filled by the cerebrospinal fluid (or cerebrospinal fluid), which also surrounds the inner cavities of the brain and spinal cord. Cerebrospinal fluid cushions the mechanical shocks of the central nervous system against the bones of the skull and spine.
Parts of the brain
The brain of all vertebrates, from fish to mammals, has the same basic structure. Its fundamental parts are the olfactory wolf, O brain, O thalamus, O optical lobe, O cerebellum it's the spinal bulb (or spinal cord).
The relative size and complexity of each of these parts varies across different vertebrate groups and this variation is related to the evolution of each group and their way of life.