Materials of a brain

Hemispheric white matter

All space between grey matter of a cerebral cortex and basal kernels is occupied by white matter. White matter of hemispheres is formed by the nerve fibrils binding a cortex of one gyrus with a cortex of other gyruses of the and inverse hemispheres, and also with underlaying formations. Topographicallies in white matter distinguish four parts which have been not sharply delimited from each other:

1. white matter in gyruses between sulcuses
2. white matter range in outside parts of a hemisphere - the semioval centre (centrum semiovale)
3. a radiate crown (corona radiata), formed radial the dispersing fibers entering into an intrinsic capsule (capsula interna) and leaving it
4. the central material of a corpus collosum (corpus callosum), an intrinsic capsule and long associative fibers.

White matter nerve fibrils divide on associative, commissural and projective.

Associative fibers bind among themselves various fields of a cortex of the same hemisphere. They are parted on short and long. Short fibers bind among themselves the next gyruses in the form of arched fascicles. Long associative fibers bridge fields of a cortex more remote from each other.

The commissural fibers which are a part of cerebral commissures, or solderings, bridge not only symmetric points, but also a cortex belonging to different lobes of inverse hemispheres.

The majority of commissural fibers goes as a part of a corpus collosum which binds among themselves parts of both hemispheres concerning neencephalon. Two cerebral solderings, commissura anterior and commissura fornicis, much less on the dimensions concern a rhinencephalon rhinencephalon and bridge: commissura anterior - olfactory lobes and both parahippocampal gyruses, commissura fornicis - hippocampuses.

Projective fibers bind a cortex of hemicerebrums to underlaying formations, and through them with periphery.

These fibers divide on centripetal (ascending, corticipetal, eisodic), spending excitation on a direction to a cortex, and centrifugal (descending, cortical-fugal, efferent). Projective fibers in white matter of a hemisphere are closer to a cortex form a radiate crown, and then their body converges in an intrinsic capsule which represents a white matter layer between a lenticular kernel (nucleus lentiformis) on the one hand, and by a caudal kernel (nucleus caudatus) and a thalamus (thalamus) - with another. On a face-to-face cut of a brain the intrinsic capsule looks like slantwise going white strip proceeding in a leg of a brain. In an intrinsic capsule distinguish a forward leg (crus anterius), - between a caudal kernel and a forward half of intrinsic surface of a lenticular kernel, a back leg (crus posterius), - between a thalamus and a back half of lenticular kernel and a knee (genu), laying on an excess place between both parts of an intrinsic capsule. Projective fibers on their length can be parted on following three systems, since the longest:

1. Tractus corticospinalis (pyramidalis) spends motorial strong-willed impulses to muscles of a trunk and extremities.
2. Tractus corticonuclearis - conduction paths to motorial kernels of cranial nerves. As all motorial fibers are collected on small space in an intrinsic capsule (a knee and forward two thirds of its back leg) at their damage to this place the secund paralysis of an opposite side of a body is observed.
3. Tractus corticopontini - pathes from a cerebral cortex to bridge kernels. By means of these pathes the great brain cortex makes inhibiting and regulating impact on cerebellum activity.
4. Fibrae thalamocorticalis et corticothalamici - fibers from a thalamus to a cortex and anatropicly from a cortex to a thalamus.

Hemispheric gray matter

The hemisphere surface, raincoat (pallium), is formed by a uniform layer of grey matter in the thickness 1,3 - 4,5 mm, containing the excitatory cells. The raincoat surface has very complex drawing consisting of sulcuses alternating among themselves in various directions and platens between them, named gyruses, gyri. The size and the form of sulcuses are subject to appreciable individual fluctuations owing to what not only a brain of various humans, but even hemispheres of the same individual on a drawing of sulcuses are not quite similar.

Deep constant sulcuses use for separation of each hemisphere into the big fields named lobes, lobi; the last are in turn parted on lobes and gyruses. Excrete five lobes of a hemisphere: frontal (lobus frontalis), parietal (lobus parietalis), temporal (lobus temporalis), occipital (lobus occipitalis) and a lobe hidden at the bottom of a lateralis sulcus, a so-called islet (insula).

High the lateralis surface of a hemisphere is differentiated on lobes by means of three sulcuses: lateralis, central and the top extremity of a parietooccipital sulcus. The lateral sulcus (sulcus cerebri lateralis) begins on a basal surface of a hemisphere from a lateralis fossa and then passes to high lateralis surface. The central sulcus (sulcus cenrtalis) begins on top to edge of a hemisphere and goes forward and downwards. The field of a hemisphere which is ahead of the central sulcus. Concerns to a frontal lobe; the part of a cerebral surface laying behind from the central sulcus, compounds a parietal lobe. As back border of a parietal lobe the extremity of a parietooccipital sulcus (sulcus parietooccipitalis), located on a medial surface of a hemisphere serves.

Each lobe consists of a number of the gyruses named in separate places lobes which confine sulcuses of a cerebral surface.

Frontal lobe. In back part of an outside surface of this lobe passes sulcus precentralis almost in parallel a direction sulcus centralis. From it in a longitudinal direction there pass two sulcuses: sulcus frontalis superior et sulcus frontalis inferior. Thanks to it the frontal lobe is parted on four gyruses. The erect gyrus, gyrus precentralis, is between central and precentral sulcus. Horizontal gyruses of a frontal lobe are: top frontal (gyrus frontalis superior), average frontal (gyrus frontalis medius) and inferior frontal (gyrus frontalis inferior).

Parietal lobe. On it approximately in parallel the central sulcus settles down sulcus postcentralis, merging usually with sulcus intraparietalis which goes in a horizontal direction. Depending on a locating of these sulcuses the parietal lobe is parted on three gyruses. The erect gyrus, gyrus postcentralis, goes behind the central sulcus in one direction with precentral sulcus. Above an interparietal sulcus the top parietal gyrus, or a lobe (lobulus parietalis superior), more low - lobulus parietalis inferior is located.

Temporal lobe. The lateral surface of this lobe has three longitudinal gyruses delimited from each other sulcus temporalis superior and sulcus temporalis inferior. Between the top and inferior temporal sulcuses it is stretched gyrus temporalis medius. Below it passes gyrus temporalis inferior.

Occipital lobe. Sulcuses of a lateralis surface of this lobe are variable and changeable. From them excrete going cross-section sulcus occipitalis transversus, bridged usually with the extremity of an interparietal sulcus.

Islet. This lobe has the triangle form. The islet surface is covered by short gyruses.

The inferior surface of a hemisphere in that its part which lays to front from a lateralis fossa, concerns a frontal lobe.

Here to in parallel medial edge of a hemisphere passes sulcus olfactorius. On a back field of a basal surface of a hemisphere two sulcuses are visible: sulcus occipitotemporalis, passing in a direction from an occipital pole to temporal and confining gyrus occipitotemporalis lateralis, and going in parallel it sulcus collateralis. Between them settles down gyrus occipitotemporalis medialis. Medially from a collateral sulcus two gyruses are located: between back part of this sulcus and sulcus calcarinus lays gyrus lingualis; between forward part of this sulcus and deep sulcus hippocampi lays gyrus parahippocampalis. It is a gyrus adjoining a brainstem, is already on a medial surface of a hemisphere.

On a medial surface of a hemisphere there is a corpus collosum sulcus (sulcus corpori callosi), going immediately over a corpus collosum and proceeding the back extremity in deep sulcus hippocampi which is referred forward and from top to bottom. In parallel and above this sulcus passes on

Medial surface of a hemisphere sulcus cinguli. As a paracentral lobe (lobulus paracentralis) is called the small field over a lingular sulcus. Behind from a paracentral lobe there is a quadrangular surface (a so-called precuneus, precuneus). It concerns to a parietal lobe. Behind a precuneus the isolated field of a cortex concerning an occipital lobe, - a wedge (cuneus) lays. Between a lingular sulcus and a corpus collosum sulcus the cingular gyrus (gyrus cinguli) which at isthmus means (isthmus) proceeds in the parahippocampal gyrus which is coming to an end with a hook (uncus) is stretched. Gyrus cinguli, isthmus and gyrus parahippocampalis form together a vaulted gyrus (gyrus fornicatus) which describes almost full circle open only from below and in front. The vaulted gyrus does not concern one of raincoat lobes. It concerns limbic range. Limbic range - a part of a new cortex of the hemicerebrums, occupying cingular and parahippocampal gyruses; is a part of limbic system. Moving apart edge sulcus hippocampi, it is possible to see the narrow jagged grey stria representing a rudimentary gyrus gyrus dentatus.