Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Nervous system (general overview of the structure and development of the nervous system)
Central nervous system
Brain - Structural and functional organization of the neocortex and basal nuclei of the cerebral hemispheres

The specific distribution of cellular and fibrous elements forms the basis for subdividing the Cerebral Cortex into fields and subfields. Cortical regions with similar Structure, topography, and developmental timelines during ontogeny are referred to cytoarchitectonic fields. In 1902–1903, K. Brodmann identified 52 cytoarchitectonic (cellular) fields in the cortex. In 1919–1920, O. Vogt and C. Vogt described 150 myeloarchitectonic regions in the cortex, taking into account its fibrous architecture. The Brain Institute of the Russian Academy of Medical Sciences (RAMS) has since developed more detailed mapping of the cytoarchitectonic fields of the human cerebral cortex.

Neocortical fields are generally subdivided into projection (or primary) fields, as well as secondary and tertiary (or associative) fields. Projection, or primary, fields are characterized by the reception of direct nerve impulses from the projection nuclei of the thalamus and metathalamus, a strict topographical Organization of afferent projections, and a proportional relationship between the area of cortical representation and the innervation density of the corresponding body surface. Examples include the fields in the postcentral gyrus (the center for general sensation), field 17 in the occipital lobe (the cortical center for Vision), and field 41 in the temporal lobe (the cortical center for Hearing), among others.

Secondary cortical fields are those located adjacent to the primary projection fields. These fields are considered peripheral extensions of the primary fields. Examples include fields 5 and 7 in the superior parietal lobule, which lie adjacent to the center for general sensation. Secondary fields perform a more differentiated and complex analysis of sensory nerve impulses compared to primary fields. While damage to projection fields results in the loss of perception for specific types of sensation, damage to secondary fields manifests as impaired recognition and evaluation of the corresponding sensory modality. Therefore, functionally, Primary and secondary fields constitute the cortical representation zones of Sensory systems. I. P. Pavlov referred to such fields as the cortical ends of analyzers. According to this view, the cerebral cortex represents a collection of the cortical ends of analyzers, each corresponding to a specific peripheral receptor field.

In accordance with the cytoarchitectonic maps of the Brain Institute, the core of the cortical analyzer for proprioceptive and cutaneous sensitivity is represented by fields 1, 2, and 3, located in the cortex of the postcentral gyrus. This zone receives proprioceptive impulses from skeletal Muscles, tendons, and joint capsules, as well as impulses from tactile, thermal, and other Skin Receptors. The largest areas of this cortical zone are occupied by the representation of the hand, vocal apparatus, and HEAD, whereas the trunk and lower limb occupy the smallest areas (Fig. 103, see color insert).

The cortical zone of the motor analyzer is represented by fields 4 and 6, located in the precentral gyrus and the paracentral lobule of the frontal lobe. The motor centers for the Muscles of the Lower Limb and the lowest PARTS OF THE trunk are located in the upper Regions of the precentral gyrus (Fig. 104, see color insert). The lower part of this gyrus houses the centers that regulate the muscles of the face and head. The motor areas of each hemisphere are connected to the skeletal muscles of the opposite side of the body. While limb muscles are connected to a single, contralateral hemisphere in an isolated manner, the Muscles of the Trunk, Larynx, and Pharynx are linked to the motor areas of both hemispheres. In both of these described centers, the size of the projection zones for various Organs depends not on the physical size of the organs themselves, but on their functional significance. For instance, the hand area in the cerebral cortex occupies a significantly larger space than the trunk and lower limb areas combined. In field 4, the axons of giant pyramidal Cells of layer V give rise to descending Projection Pathways: the corticospinal and corticonuclear tracts. The fibers of these tracts lead to the motor Neurons of the Spinal Cord and Brainstem. Fields 3 and 4 merge directly into one another deep within the central sulcus, ensuring the closest possible functional contact. Consequently, cortical fields 1, 2, 3, 4, and 6 are collectively referred to as the somatosensory cortical zone.

The core of the Auditory Analyzer (fields 41, 42) is located On the surface of the middle part of the superior temporal gyrus facing the insula. Conduction pathways from the auditory receptors of both the left and right sides project to each hemisphere.

The core of the visual analyzer is situated on the Medial surface of the occipital lobe of the cerebral hemisphere, flanking both sides ("along the banks") of the calcarine sulcus (fields 17, 18, 19). The visual analyzer core of the right hemisphere is connected via pathways to the lateral half of the right eye's retina and the medial half of the left eye's retina, whereas the visual analyzer core of the left hemisphere is connected to the lateral half of the left eye's retina and the medial half of the right eye's retina.

The cortical end of the olfactory analyzer comprises the uncus, as well as the paleocortex (old cortex) and archicortex (primitive cortex). The paleocortex is located in the region of the hippocampus and the dentate gyrus, while the archicortex is situated in the area of the anterior perforated substance, the septum pellucidum, and the olfactory gyrus. Due to the close anatomical proximity of the olfactory and gustatory analyzer cores, the Senses of Smell and Taste are closely interrelated. The taste and smell analyzer cores of both hemispheres are connected via Neural Pathways to receptors on both the left and right sides.

The described cortical ends of the analyzers perform the analysis and synthesis of signals originating from the external and internal environments of the Organism, constituting the first signaling system of reality (I. P. Pavlov). In contrast to the first, the second signaling system is unique to humans and is closely associated with The Development of articulated speech.

Tertiary, or associative, fields occupy more than half of the total surface of the cerebral hemispheres in the human brain. In the frontal lobe, associative fields include fields 8–10 and 44–47; in the parietal lobe, fields 5, 7, 39, and 40; and in the temporal lobe, fields 22, 37, and 38. The defining criterion for identifying tertiary fields is their tight interconnection with the associative nuclei of the thalamus. Functionally, these fields are involved in the organization of complex behavioral acts.

Associative fields occupy their most substantial region within the frontal lobe. Specifically, fields 11 and 12 occupy the orbitofrontal region, while fields 8–10 and 44–47 occupy the prefrontal region.

Afferent fibers terminating in the fields of the orbitofrontal region originate from neurons of the septum pellucidum, the tectum of the Midbrain, and nonspecific thalamic nuclei. This region maintains reciprocal connections with the fields of the prefrontal and temporal areas. Efferent projection pathways project to the hypothalamic nuclei. Functionally, the orbitofrontal cortex is regarded as a vital link in the limbic system. Fields 44–47 of the prefrontal region occupy the inferior frontal gyrus and are functionally linked to speech production.

Fields 8–10 receive a significant number of afferent fibers originating from fields 18 and 19 of the occipital lobe and other cortical areas.

Fields 5 and 7 of the parietal lobe receive afferent fibers from primary projection fields 3 and 4, as well as from associative thalamic nuclei, and are functionally associated with stereognosis (The ability to perceive the Physical Properties of objects by Touch).

Fields 39 and 40 in the parietal lobe are exceptionally well-developed in the human brain. Functionally, field 40 is involved in the organization of complex movements, including handwriting. Field 39, located adjacent to the visual analyzer core, processes signals (impulses) associated with written language.

Field 22 of the temporal lobe contains the core of the cortical end of the auditory analyzer responsible for perceiving the verbal designation of objects. Field 21 houses the projection area of the vestibular apparatus.

Thus, the associative fields of the cortex are engaged in the most complex processes characteristic of human life and activity.

The function of speech is one of the specific attributes unique to humans, serving as the foundation for Abstract thought. Fields 44 and 45 (Broca's area) and field 22 (Wernicke's area), located in the left cerebral hemisphere of right-handed individuals, are directly associated with speech function in the cerebral cortex.

Broca's area is located in the inferior frontal gyrus of the frontal lobe and borders the region of the cortical motor center.

Fields 44 and 45 (Broca's area) contain the centers of the speech analyzer. This area borders the lower sections of the precentral gyrus, which serve as analyzers for movements produced by the contraction of Head and Neck muscles. Within this portion of the speech-motor analyzer, movements of all the muscles of the Lips, Cheeks, Tongue, and larynx involved in spoken language production (articulation of words and sentences) are analyzed. Damage to this cortical region (field 44) leads to motor aphasia, i.e., the loss of the ability to articulate words. This aphasia is not associated with any loss of the Muscle contraction capacity required for speech production. Furthermore, lesions in field 44 do not impair the ability to produce non-verbal sounds or sing.

The central parts of the inferior frontal gyrus (field 45) house the core of the speech analyzer associated with singing. Damage to field 45 is accompanied by agrammatism, wherein the ability to construct meaningful sentences from individual words is lost. The speech of such patients consists of semantically disconnected strings of words.

In humans, field 46 achieves significant development; it lies directly adjacent to Broca's area and is functionally related to the perception of rhythmic sound sequences during the Ontogenetic development of speech function.

Wernicke's center (area) is located in the superior temporal gyrus (field 22). This area also incorporates fields 42, 40, and 37, which occupy adjacent cortical regions. Destruction of this area in the left hemisphere of right-handed individuals results in verbal agnosia (the inability to comprehend speech). Neurons of Wernicke's area receive fibers from the medial geniculate body and the pulvinar nuclei of the thalamus.

Speech activity requires the Structural and functional integrity of the speech-auditory, speech-visual, and speech-motor areas of the cerebral cortex, as well as their connections with thalamic nuclei, subcortical nuclei, and cranial nerve nuclei.

Structural and functional ORGANIZATION OF THE basal nuclei. The caudate and lentiform nuclei are separated by White matter composed of myelinated fibers, known as the corpus striatum. Functionally, the structures of the corpus striatum represent a crucial link in the extrapyramidal system, which regulates complex automated motor acts, organizes facial expressions, and modulates muscle tone. By integrating various brain structures, the extrapyramidal system Functions in close coordination with the pyramidal and limbic systems, playing a vital role in the organization of movement and mental processes.

Functionally, the amygdala is considered part of the limbic system, which regulates autonomic and neuroendocrine functions. The primary afferent fibers to the neurons of the amygdala originate in the structures of the olfactory brain, hypothalamic nuclei, as well as the cortex of the temporal and frontal lobes. Efferent fibers from the amygdala project to the hypothalamic nuclei, the reticular Formation of the midbrain and Pons, the dorsal motor Nucleus of the Vagus nerve, and neocortical areas; reciprocal connections also exist between the amygdala and the substantia nigra, as well as neurons of the brainstem reticular formation.