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White matter of the cerebral hemispheres
Last reviewed: 18.10.2021
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The white matter of the cerebral hemispheres is represented by various systems of nerve fibers, among which are the following:
- associative;
- commissural and
- projection.
They are considered as conducting ways of the brain and spinal cord. Associative nerve fibers that emerge from the hemisphere cortex (extracortical) are located within the same hemisphere, connecting different functional centers. The commissural nerve fibers pass through the spikes of the brain (corpus callosum, anterior spike). Projective nerve fibers from the cerebral hemisphere to the underlying parts (intermediate, middle, etc.) and to the spinal cord, as well as the following in the opposite direction from these formations, constitute the inner capsule and its radiate crown (corona radiata).
The inner capsule (capsula interna) is a thick, angled plate of white matter. On the lateral side, it is bounded by a lenticular nucleus, and with the medial - the head of the caudate nucleus (front) and the thalamus (behind). The inner capsule is divided into three sections. Between the caudate and lenticular nuclei is the anterior foot of the inner capsule (crus anterius capsulae internae) between the thalamus and the lenticular nucleus - the back leg of the inner capsule (crus posterius capsulae internae). The junction of these two divisions at an angle open laterally forms the knee of the inner capsule (genu capsulae internae).
In the inner capsule pass all the projection fibers that connect the cerebral cortex with other parts of the central nervous system. In the knee of the inner capsule, the fibers of the cortical-nuclear path are located, which is guided from the cortex of the precentral gyrus to the motor nuclei of the cranial nerves. In the anterior part of the posterior stem, directly adjacent to the knee of the inner capsule, there are cortico-spinal fibers. This motor way, like the previous one, begins in the precentral gyrus and follows the motor nuclei of the anterior horns of the spinal cord.
Behind the listed conductive paths in the posterior stalk are thalamocortical (thalamotemennye) fibers. They are represented by the outgrowths of the thalamus cells, bound to the cortex of the postcentral gyrus. This conductive pathway contains fibers of conductors of all kinds of general sensitivity (pain, temperature, touch and pressure, proprioceptive). Even more posteriorly from this tract in the central sections of the posterior stem is the temporomandibular-occipital-bridge path. The fibers of this pathway start from the cells of different parts of the cortex of the occipital, parietal and temporal lobes of the hemisphere and follow to the nuclei of the bridge located in its anterior (basilar) part. In the posterior sections of the posterior pedicle, the auditory and visual pathways are located. Both originate from the subcortical centers of hearing and vision and end in the corresponding cortical centers. The front leg of the inner capsule contains the frontal-bridge path.
These are only the most important conducting paths, the fibers of which pass in the inner capsule.
The fibers of the ascending conducting paths, diverge in different directions in the cortex of the cerebral hemispheres, form the so-called radiate crown (corona radiata). The fiber of the descending pathways of the inner capsule in the form of compact bundles are sent to the midbrain.
The corpus callosum contains fibers (commissural pathways) that go from one hemisphere to the other and connect the parts of the cortex that belong to the right and left hemispheres, in order to unite (coordinate) the functions of both halves of the brain into one. The corpus callosum is a thick, specially bent plate consisting of transverse fibers. The free upper surface of the corpus callosum, facing the longitudinal slit of the large brain, has a gray cover (indusium griseum) - a thin plate of gray matter.
On the sagittal section of the brain, bends and parts of the corpus callosum can be distinguished: the genus, which extends downwards into the beak (rostrum), and then into the terminal plate (lamina terminalis). The middle part is called the trunk (truncus) of the corpus callosum. At the back, the trunk continues into the thickened part - the splenium. The transverse fibers of the corpus callosum in each hemisphere of the large brain form the radiance of the corpus callosum (radiatio corporis callosi). Fibers of the anterior part of the corpus callosum - the knee - round the anterior part of the longitudinal slit of the brain and connect the cortex to the frontal lobes of the right and left hemispheres. Fibers of the central part of the corpus callosum - the trunk - connect the gray matter of the parietal and temporal lobes. In the platen there are fibers enveloping the posterior part of the longitudinal slit of the large brain, which connect the cortex of the occipital lobes.
Under the corpuscular body is the fornix. The arch consists of two arcuate curved bands, connected in the middle part by means of transversely extending fibers - the spike of the arch (comissura fornicis). The middle part is called the body of the vault (corpus fornicis). Ahead and down it continues into the rounded twin stitch - column of the vault (columna fornicis). The right and left pillars of the arch are directed downwards and somewhat laterally to the base of the brain, where it ends in the right and left mastoid bodies. Behind the body of the arch also extends into a pair of flat strands - the leg of the vault (crus fornicis), fused with the lower surface of the corpus callosum. The paired leg of the arch on the right and left side gradually leaves laterally and down, separated from the corpus callosum, is even more flattened and merges one side with the hippocampus, forming the fimbria hippocampi fimbria. The other part of the fimbria is free and faces the lower horn of the lateral ventricle. The fimbriae of the hippocampus in the hook ends, thus connecting the temporal lobe of the terminal brain with the intermediate brain.
In front of the arch in the sagittal plane there is a transparent septum (septum pellucidum), which consists of two plates lying parallel to each other. Each plate of the transparent septum (lamina septi pellucidi) is stretched between the body and the arch of the arch in the rear, the corpus callosum at the top, the knee and the beak of the corpus callosum in front and below. Between the plates of the transparent septum is a slit cavity of the transparent septum (cavum septi pellucidi), containing a transparent liquid. The plate of the transparent septum serves as the medial wall of the anterior horn of the lateral ventricle. In front of the pillars of the arch there is an anterior spike (comissura rostralis, s. Anterior), the fibers of which are oriented transversely. On the sagittal section, the spike has the shape of a small oval. The front part of the spike is thin, joins the gray substance of the olfactory triangles of both hemispheres. The large posterior part contains nerve fibers that connect the bark of the anterior-medial parts of the temporal lobes.
The white matter of the hemisphere includes fibers that connect different parts of the cortex within one hemisphere (associative fibers) or the cortex with the subcortical centers of the hemisphere. Along with short associative nerve fibers in white matter, large long beams that have a longitudinal orientation and connect distant regions of the cerebral cortex far apart are distinguished.