Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovskyi 2008

Special Section
Nervous system, systema nervosum - Special Section
Brain - Telencephalon - Limbic system

The limbic system is understood as a complex of telencephalic, diencephalic, and mesencephalic structures that surround the upper part of the Brainstem and form the substrate for the manifestation of the body's most general states (Sleep, activity, emotions, motivation, etc.). Because the limbic system plays a primary role in mediating emotions such as pain, pleasure, anger, rage, fear, grief, sexual interest, docility, and affection, it is sometimes referred to as the "visceral" or "emotional" Brain.

The main part of the limbic system consists of structures belonging to the paleocortex, neocortex, and archicortex, located primarily on the Medial surface of the cerebral hemispheres, as well as numerous closely associated subcortical structures.

* The term "limbic system" (limbus - border/edge) was proposed by P. MacLean (1952).

The limbic system includes the olfactory bulbs, olfactory peduncles, olfactory tracts, olfactory tubercles, anterior perforated substance, diagonal band of Broca, and olfactory gyri (lateral and medial). All these structures are grouped under the general term "olfactory part".

On the medial surface of the hemispheres, the limbic system includes the anterior part of the brainstem and interhemispheric commissures, which are bounded by a large arcuate gyrus, the dorsal half of which is occupied by the cingulate gyrus, and the ventral half by the parahippocampal gyrus (Fig. 158). Posteriorly, the cingulate and parahippocampal gyri form the retrosplenial region or isthmus. Anteriorly, between the antero-inferior ends of these gyri, lies the cortex of the posterior orbital surface of the frontal lobe, the anterior lobe, the insula, and the temporal pole. The parahippocampal gyrus must be distinguished from the hippocampal formation, which is formed by the body of the hippocampus, the dentate gyrus, the perizonal vestige of the archicortex, and, according to some authors, the subiculum and presubiculum (i.e., the base and pre-Base of the hippocampus). The hippocampus, together with the cerebral lobes, influences learning, cognitive Processing of new information, memorization, spatial relationships, and memory. Memory impairment is a result of damage to the limbic system. People with such disorders forget recent events and cannot commit anything to memory. According to recent data, the hippocampus (sea horse gyrus), along with other structures, modulates the expression of emotions such as anger and fear.

Subcortical structures of the limbic system include the basal nuclei, non-specific thalamic nuclei, Hypothalamus, habenula, and, according to some authors, the Midbrain reticular formation. The basal nuclei are the oldest structures of the limbic system. They are represented by the paleostriatum, archistriatum, and neostriatum. In humans, the paleostriatum includes the globus pallidus, globus pallidus or simply pallidum, the archistriatum includes the amygdaloid body, and the neostriatum includes the putamen and caudate Nucleus.

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Fig. 158. Brain structures forming the limbic system

Among the neocortical structures, some authors include the temporal and frontal regions and the intermediate zone in the limbic system. This zone is located between the piriform and periamygdaloid cortex on one side, and the orbitofrontal and temporopolar cortex on the other. It is sometimes referred to as the orbito-insulotemporal cortex.

The limbic system represents a complex network of ascending and descending pathways that form numerous closed neural loops within this system, connecting its various structures. Among these, the following circuits are distinguished: 1) stria terminalis - hypothalamus - amygdaloid area; 2) hippocampus - fornix - thalamic tract (of Vicq d'Azyr); 3) hippocampus - via the fornix to the mammillary bodies - anterior thalamic nuclei - cingulate gyrus - and via the parahippocampal gyrus back to the hippocampus (Papez circuit). Papez (J. W. Papez, 1937) viewed this circuit as a specific substrate for emotion, learning, and memory.

The ascending Pathways of the limbic system are anatomically insufficiently understood. It is known that, along with classical sensory pathways, they also include diffuse pathways that do not travel within the medial lemniscus. The descending pathways of the limbic system, which connect it to the hypothalamus, reticular formation, and other brainstem structures, run primarily within the medial Forebrain bundle, stria terminalis, and fornix. Fibers originating from the hippocampus terminate mainly in the lateral hypothalamus, infundibulum, preoptic area, and mammillary bodies.

Thus, the limbic system, occupying a central position within the CNS, is capable of rapidly engaging in virtually all bodily Functions aimed at active ADAPTATION TO ENVIRONMENTAL conditions. The limbic system receives afferent excitatory impulses from structures of the lower brainstem, olfactory structures of the brain, and the neocortex. Through the network of connections, these excitations rapidly reach all necessary Regions of the Limbic System and instantly, via the fibers of the medial forebrain bundle or direct neostriato-tegmental pathways, activate or inhibit the executive motor and autonomic centers of the lower brainstem and Spinal Cord. This achieves The formation of a functional system "specialized" for these specific conditions, which ensures that the Organism achieves a beneficial result.