Each cerebral hemisphere can be divided into three main regions. The outermost region, the cerebral cortex, is a thin layer (2 to 4 millimeters thick) made up of gray matter, consisting of neuron cell bodies, dendrites, glial cells, and blood vessels. The middle region, or white matter, is primarily composed of myelinated nerve fibers organized into three types of large tracts: association fibers, commissures, and projection fibers. Association fibers connect different areas within the same cerebral hemisphere, while commissures, such as the corpus callosum, bridge the gap between the two hemispheres. Projection fibers link the cerebral cortex to vital structures like the thalamus, brainstem, and spinal cord.
Finally, deep within the white matter lies the innermost region, the basal nuclei, housing clusters of neuron cell bodies, which play a crucial role in motor functions. The first two nuclei, globus pallidus and putamen, are adjacent and together form the lentiform nucleus. The third nucleus is the caudate nucleus, which, when viewed from the side, resembles an arch with a large head and a slender tail-like structure above the diencephalon.
