Plan
► Anatomy of telencephalon.
► Physiology of telencephalon.
► Physiology of limbic system.
Anatomy of Telencephalon
The telencephalon develops from the prosencephalon and consists of well-developed paired parts - right and left hemispheres connected with the medial part. The hemispheres are separated by a longitudinal fissure and connected across the midline by a massive bundle of axons called the corpus callosum. Below the corpus callosum the fornix is located represented by two curved fibrous cords connected in the medial part and diverging in the upper and lower parts forming columns and crura of the fornix.
In front of the columns the anterior commissure is located. Between the frontal part of the corpus callosum and fornix there is a thin vertical plate of the brain substance - a transparent partition. Hemispheres consist of gray and white matter. The structures of the hemisphere are: pallium formed by the superficial layer of the gray matter - the cortex; rhinencephalon, and aggregations of the gray matter inside the hemispheres - basal nuclei. The last two regions form the oldest from the point of view of the evolution part of the hemispheres. The telencephalon contains cavities - lateral ventricles.
In each hemisphere three surfaces are distinguished: superolateral surface - convex surface following the shape of the fornix, medial surface - flat surface facing the analogous surface of the other hemisphere, and lower surface - of irregular shape. The surface of the hemisphere has an intricate pattern formed by sulci going in different directions with ridges between them - gyri. The size and shape of sulci and gyri exhibit significant individual variations.
However, there exist several permanent sulci that are distinctly seen in all individuals and are the first to appear in the embryonic development. They divide the hemispheres into large areas called lobes. Each hemisphere is divided into five lobes: frontal, parietal, occipital, temporal and a concealed lobe, or insula, buried deeply within the lateral (Sylvian) fissure. The frontal and parietal lobes are separated by the central sulcus, and parietal and occipital lobes - by the parieto-occipital fissure. The temporal lobe is separated from other lobes by the lateral fissure (see Fig. 12.1).