Frontal lobes of the brain
Last reviewed: 23.04.2024
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In the anterior part of each hemisphere of the large brain is the frontal lobe (lobus frontalis). It ends at the front with a frontal pole and is bounded from below by a lateral furrow (sulcus lateralis; sylvian furrow), and behind it by a deep central furrow. The central furrow (sulcus centralis; Roland furrow) is located in the frontal plane. It starts in the upper part of the medial surface of the cerebral hemisphere, cuts across its upper edge, descends, without interruption, along the upper-lateral surface of the hemisphere down and ends slightly before reaching the lateral furrow.
In front of the central sulcus, almost parallel to it, is the precentral furrow (sulcus precentralis). It ends at the bottom, not reaching the lateral furrow. The precentral furrow is often interrupted in the middle part and consists of two independent furrows. The upper and lower frontal furrows (sulci frontales superior et inferior) are directed from the precentral groove. They are located almost parallel to each other and divide the upper-lateral surface of the frontal lobe into convolutions. Between the central groove behind and the precentral groove in front is the precentral gyrus (gyrus precentralis). Above the upper frontal sulcus lies the upper frontal gyrus (gyrus frontalis superior), occupying the upper part of the frontal lobe. Between the upper and lower frontal furrows the middle frontal gyrus extends (gyrus frontalis medius).
The lower frontal gyrus (gyrus frontalis inferior) is located from the lower frontal sulcus. In this gyrus, the branches of the lateral sulcus extend from below: the ascending branch (ramus ascendens) and the anterior branch (ramus anterior), which divide the lower part of the frontal lobe, hanging over the anterior part of the lateral sulcus, into three parts: the capillary, triangular and orbital. The covering part (frontal cover, pars opercularis, s. Operculum frontale) is located between the ascending branch and the lower part of the precentral groove. This part of the frontal lobe was given such a name because it covers the island island (islet) lying in the depth of the furrow. The triangular part (pars triangularis) is between the ascending rear and the front branch in front. The glabular part (pars orbitalis) lies downward from the anterior branch, continuing on the lower surface of the frontal lobe. At this point the lateral groove widens, in connection with which it is called the lateral fovea of the large brain (fossa lateralis cerebri).
The function of the frontal lobes is associated with the organization of arbitrary movements, the motor mechanisms of speech and writing, the regulation of complex forms will result in the processes of thinking.
The afferent systems of the frontal lobe include the conductors of deep sensitivity (they terminate in the precetral gyrus) and numerous associative connections from all other parts of the brain. The upper layers of the cortex of the frontal lobes are included in the work of the kinesthetic analyzer: they participate in the formation and regulation of complex motor acts.
In the frontal lobes, various efferent motor systems begin. In the V layer of the precentral gyrus, there are giant-pyramidal neurons that make up the cortical-spinal and cortical-nuclear pathways (pyramidal system). From the extensive extrapyramidal sections of the frontal lobes in the premotor zone of its cortex (mainly from cytoarchitectonic fields 6 and 8) and its medial surface (fields 7, 19), numerous conductors to the subcortical and stem formations (fronto-thalamic, front-palpidar, front-ribbed, etc.). In the frontal lobes, in particular at their poles, frontal-bridge-cerebellar pathways are included in the system of coordination of voluntary movements.
These anatomical-fizologicheskie features explain why the lesions of the frontal lobes violate mainly the motor functions. In the sphere of higher nervous activity, motor activity of the speech act and behavioral acts associated with the implementation of complex motor functions are also violated.
The entire cortical surface of the frontal lobes is anatomically divided into three components: dorso-lateral (convective), medial (forming interhemispheric fissure) and orbital (basal).
The anterior central gyrus contains the motor projection areas for the musculature of the opposite side of the body (in the order opposite to its location on the body). In the posterior part of the second frontal gyrus, there is a "center" of turning the eyes and head in the opposite direction, and in the posterior part of the lower frontal gyrus the Broca region is localized.
Electrophysiological studies have shown that neurons of the premotor cortex can respond to visual, auditory, somatic, olfactory and taste stimuli. The premotor region is capable of modifying motor activity due to its connections to the caudate nucleus. It also provides for sensor-motor relationships and directional attention. Frontal lobes in modern neuropsychology are characterized as a block of programming, regulation and control of complex forms of activity.
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