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Brain

 
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Last reviewed: 31.05.2018
 
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The brain (encephalon) with its surrounding shells is located in the cavity of the cerebral part of the skull. In this regard, its convex upper-lateral surface in shape corresponds to the inner concave surface of the cranial vault. The lower surface - the base of the brain - has a complex relief corresponding to the shape of the cranial pits of the inner base of the skull.

The mass of the brain of an adult varies from 1100 to 2000. The length of the brain is on average 160-180 mm, the largest transverse dimension is 140 mm. The female brain is on average slightly shorter than the male. The weight of the brain of an adult male is 1400 g on average, and of a woman is 1200 g. The greatest weight of the brain is in people aged 20 to 25 years. The brain of brachycephalians is on average heavier than the brain of dolichocephalans.

There is no direct relationship between the weight of the brain and the intellectual capacity of man. For example, the weight of the brain of writer AN Turgenev - 2012, the poet Byron - 1807, the philosopher I. Kant - 1600 g, the poet IF Schiller - 1580 g, the doctor Broca - 1484 g, the doctor G. Dupuytren -1437 g, the poet A. Dante - 1420 g, the painter A. Tideman - 1254. It is known that other people of an outstanding mind possessed a brain with a relatively small weight. In idiots, the brain has a particularly low weight, sometimes it does not even reach 300 g. Experience shows that in spiritually more developed people, the brain of a more significant weight often occurs. However, the high weight of the brain does not in any way indicate a higher spiritual development. However, the weight of the brain must exceed a certain minimum rate, so that the mental functions can be correctly performed. For men, the brain is considered to be the minimum norm in 1000 g, and for women - 900 g. The spinal cord has about 2% of the brain weight and is 34-38 g.

Brain.  The hemisphere of the brain

When examining the preparation of the brain, three of its largest components are clearly visible: the cerebral hemisphere, the cerebellum and the brain stem.

The cerebral hemispheres (hemispheriae cerebrales) in an adult are the most highly developed, the largest and most functionally most important part of the central nervous system. The departments of the cerebral hemispheres cover all other parts of the brain.

The right and left hemispheres are separated from each other by a deep longitudinal fissure of the large brain (fissura longitudinalis cerebralis), which deep in between the hemispheres reaches a large spike of the brain, or corpus callosum. In the posterior sections, the longitudinal slot connects to the transverse cleft of the large brain (fissura transversa cerebralis), which separates the cerebral hemispheres from the cerebellum.

On the upper-lateral, medial and lower (basal) surfaces of the cerebral hemispheres are deep and shallow furrows. Deep furrows divide each of the hemispheres into parts of the large brain (lobi cerebrales). The fine furrows are separated from each other by the convolutions of the large brain (gyri cerebrales).

The lower surface (facies inferior), or the base of the brain, is formed by the ventral surfaces of the cerebral hemispheres, the cerebellum and the most accessible for viewing by the ventral divisions of the brain stem.

Brain.  The lower surface of the brain

On the basis of the brain, in the anterior regions formed by the lower surface of the frontal lobes of the cerebral hemispheres, it is possible to detect olfactory bulbs (bulbi olfactorii). They have the appearance of small bulges, located on the sides of the longitudinal slit of the large brain. 15-20 thin olfactory nerves (nn. Olfactorii - I pairs of cranial nerves) fit the ventral surface of each of the olfactory bulbs from the nasal cavity through the holes in the plate of the lattice. When the brain is removed from the skull, the olfactory nerves break off and are therefore not visible on the isolated preparation.

From the olfactory bulb back stretch the stern - the olfactory tract (tractus olfactorius). The posterior sections of the olfactory tract thicken and expand, forming the olfactory olfactory (trigonum olfactorium). The back side of the olfactory triangle passes into a small area with a large number of small holes remaining after removal of the choroid. This is anterior perforated substance (substantia perforata rostralis, s. Anterior). Here through the holes of the perforated substance deep into the brain penetrate the arteries. The medial of the perforated substance, closing the posterior sections of the longitudinal slit of the large brain on the lower surface of the brain, is a thin, gray color, an easily tearing terminal, or terminal plate (lamina terminalis). Behind this plate is a visual crosshair (chiasma opticum). It is made up of fibers that follow the optic nerves (nn opticum - the second pair of cranial nerves) penetrating into the cavity of the skull from the orbits. From the visual cross in the posterolateral direction, two visual tracts (tractus opticus) depart.

A gray tuber (tuber cinereum) is attached to the posterior surface of the optic chiasm. The lower parts of the gray hillock are elongated in the form of a tapering tubule, which is called the funnel (infundibulum). At the lower end of the funnel is a rounded formation - the hypophysis (hypophysis), the gland of internal secretion. The pituitary gland lies in the cavity of the skull in the pit of the Turkish saddle and when the brain drug is removed from the skull it remains in this depression, breaking off from the funnel.

To the gray mound at the rear adjoin two white spherical elevations - mastoid bodies (corpora mamillaria). Behind the visual tracts are two longitudinal white ridges - the legs of the brain (pedunculi cerebri), between which is a depression - the intercostal fossa (fossa interpeduncularis), bounded from the front by mastoid bodies. The bottom of this fossa is formed by the rear perforated substance (substantia perforata interpeduncularis posterior), through the holes of which the arteries feeding it enter the brain. On the medial, facing surfaces of the legs of the brain, the roots of the right and left oculomotor nerves are visible (nn. Oculomotorius - III pair of cranial nerves). The lateral surfaces of the legs of the brain go around the block nerves (nn. Trochleares - IV pair of cranial nerves), the roots of which leave the brain not on the basis of it, as in all the other 11 pairs of cranial nerves, but on the dorsal surface, behind the lower mound roofs of the midbrain The sides of the bridle of the upper cerebral sail.

The legs of the brain behind come out of the upper sections of a wide transverse cushion, which is designated as a bridge (pons). The lateral sections of the bridge continue into the cerebellum, forming a paired middle cerebellar peduncle (pedunculus cerebellaris medius).

On the boundary between the bridge and the middle cerebellar legs on each side, one can see the spine of the trigeminal nerve (n. Trigeminus - V pair of scurvy nerves).

Below the bridge are the anterior sections of the medulla oblongata, which are represented by medially arranged pyramids, separated from each other by the anterior median slit. The lateral elevation of the pyramid is the olive. On the border of the bridge and the medulla oblongata, on the sides of the anterior median slit, the roots of the abducent nerve (n. Abducens - VI cranial nerve) leave the brain. Still laterally, between the middle cerebellar peduncle and the olive tree, the roots of the facial nerve (n. Facialis - VII cranial nerve) and the pre-cochlear nerve (n. Vestibulocochlearis - VIII cranial nerve) are successively located on each side. The roots of the following cranial nerves pass in front of the back of the olive in a barely noticeable furrow: glossopharyngeus (IX nerve), vagus (n. Vagus - X nerve) and accessory (n. Accessorius - XI nerve). The roots of the accessory nerve also extend from the spinal cord in its upper part - spinal roots (radices spinales, spinal cord, pars spinalis). In the furrow separating the pyramid from the olive, there are the roots of the hyoid nerve (n.hypoglossus - XII pair of cranial nerves).

The medial surface of the cerebral hemisphere, some structures of the trunk of the brain (truncus encephalicus) and the cerebellum are seen on the medial sagittal section of the brain, along the longitudinal slit of the large brain.

Brain

The vast medial surface of the cerebral hemispheres hangs over the much smaller cerebellum and brain stem. On this surface, as well as on other surfaces, there are furrows, which are separated from each other by the convolutions of the large brain.

The areas of the frontal, parietal and occipital lobes of each hemisphere are separated from the well-marked medial spike of the brain - corpus callosum - by the furrow of the corpus callosum (sulcus corporis callosi). The middle part of the corpus callosum is called the trunk (truncus). The anterior parts of it, bending downwards, form a knee (genu). Even more down the knee of the corpus callosum is thinned and gets the name of the beak (rostrum), which goes down to the terminal plate (lamina terminalis). The latter, as noted, fuses with the anterior surface of the visual crossover. The posterior parts of the corpus callosum are markedly thickened and terminate freely in the form of a splenium.

Under the corpus callosum is a thin white plate - the fornix. Gradually moving away from the corpus callosum and forming an arcuate bend forward and downward, the body of the arch continues into the column (columna) of the arch. The lower part of each column of the arch first approaches the terminal plate, and then retreats laterally and ends back, ending in the mastoid. Between the pillars of the arch in the rear and the terminal plate in front is a transversely moving bundle of nerve fibers that have a white oval shape on the cut, a commissure rostralis (s. Anterior). Spike, like transverse fibers of the corpus callosum, connects the hemispheres of the cerebrum, its anterior parts.

The site, bounded from above and from the front by a corpus callosum, from below with its beak, terminal plate and anterior soldering, and behind it by a pillar of the arch, is occupied by a thin sagittally oriented plate of the medulla with a transparent septum pellucidum.

All the listed entities belong to the final brain (telencephalon). The structures located below, with the exception of the cerebellum, belong to the brainstem. The most forward sections of the brainstem are formed by the right and left visual crescents - the posterior thalamus (thalamus dorsalis). The thalamus is located downward from the body of the arch and the corpus callosum and behind the pillar of the arch. On the median section only the medial surface of the posterior thalamus is distinguishable. It stands out interthalamic fusion (adhesio interthalamica). The medial surface of each posterior thalamus restricts the sideward, vertically located cavity of the third ventricle to the side. Between the anterior end of the thalamus and the column of the arch, there is an interventricular opening (foramen interventriculare), through which the lateral ventricle of the cerebral hemisphere communicates with the cavity of the third ventricle. In the posterior direction from the interventricular orifice, the hypothalamic (subthalamic) furrow (sulcus hypothalamicus) stretches, bending around the thalamus from below. The formations located downward from this furrow refer to the hypothalamus (hypothalamus). This is a visual crossover, a gray mound, a funnel, a pituitary gland and mastoid body structures that participate in the formation of the bottom of the third ventricle.

Above and behind the visual hillock, under the platbands of the corpus callosum, is the pineal body (corpus pineale), which is the gland of internal secretion. The anterior sections of the pineal body are fused with a thin transverse strand, rounded on the sagittal section. This is the epithalamic adhesion (commissura epithalamica). The thalamus (visual hillock), the hypothalamus, the third ventricle, the pineal body belong to the intermediate brain (diencephlon).

More caudal than the thalamus are the formations related to the middle brain (mesencephalon). Below the pineal body is the roof of the midbrain (plate of quadruple, tectum mesencephalicum), consisting of two upper and two lower hills. The ventral plate of the midbrain roof is located the pedicle of the brain (pedunculus cerebri), separated from the plate by the aqueduct of the midbrain.

The aqueduct of the midbrain (aqueductus mesencephali) connects the cavities of the III and IV ventricles. Even more posterior are the median sections of the bridge and the cerebellum, related to the posterior brain (metencephalon), and the medulla oblongata (medulla oblongata). The cavity of these parts of the brain is the IV ventricle (ventriculus quartos). The bottom of the IV ventricle is formed by the dorsal surface of the bridge and the medulla oblongata, which forms on the whole brain a rhomboid fossa (fossa rhomboidea). A thin plate of white matter that stretches from the cerebellum to the roof of the midbrain is called the upper cerebral sail (velum medullare rostralis, s. Superius). From the lower surface of the cerebellum back, to the medulla oblongata, extends the lower cerebral sail (velum medullare caudale, s. Inferius).

There are 5 divisions of the brain, developing from five cerebral bubbles:

  1. the final brain;
  2. intermediate brain;
  3. middle brain;
  4. hindbrain;
  5. the medulla oblongata, which at the level of the large occipital orifice passes into the spinal cord.

trusted-source[1], [2], [3]

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It is important to know!

The occipital lobe (lobus occipitalis) is located behind the parieto-occipital furrow and its conditional continuation on the upperlateral surface of the hemisphere. In comparison with other shares, it has small dimensions. Read more..

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