The brain is an organ that regulates all body functions. It is included in the CNS. Leading scientists and physicians from different countries have been and continue to be engaged in the study of the brain.
General information
The brain includes 25 billion neurons that form gray matter. The weight of an organ varies by gender. For example, in men, its weight is about 1375 g, in women - 1245 g. On average, its share in the total body weight is 2%. At the same time, scientists have found that the level of intellectual development is not related to the mass of the brain. Mental abilities are affected by the number of connections created by the organ. Brain cells are neurons and glia. The former generate and transmit impulses, the latter perform additional functions. There are cavities inside the brain. They are called stomachs. The cranial nerves depart from the organ we are considering in different parts of the human body. They are paired. In total, 12 pairs of nerves leave the brain. Three membranes cover the brain: soft, hard and arachnoid. There are spaces between them. They circulate cerebrospinal fluid. It acts as an external hydrostatic medium for the CNS, as well asensures the excretion of metabolic products. The shells of the brain differ in their structure and the number of vessels passing through them. However, all of them protect the contents of the upper part of the skull from mechanical damage.
Spider MO
Arachnoidea encephali is separated from the dura by a capillary network in the subdural space. It does not go into the recesses and furrows, like a vascular one. However, the arachnoid membrane is thrown over them in the form of bridges. As a result, a subarachnoid space is formed, which is filled with a clear liquid. In some areas, mainly on the basis of the brain, there is a particularly good development of the subarachnoid spaces. They form deep and wide receptacles - tanks. They contain cerebrospinal fluid.
Vascular (soft) MO
Pia mater encephali directly covers the cerebral surface. It is presented in the form of a transparent two-layer plate, which extends into the cracks and furrows. In the vascular MO there are chromatophores - pigment cells. Especially a lot of them revealed on the basis of the brain. In addition, there are lymphoid, mast cells, fibroblasts, numerous nerve fibers and their receptors. Parts of the soft MO accompany the arterial vessels (medium and large), reaching the arterioles. Virchow-Robin spaces are located between their walls and shell. They are filled with cerebrospinal fluid and communicate with the subarachnoid space. Elastic andcollagen fibrils. Vessels are suspended on them, by means of which conditions are created for their displacement during pulsation without affecting the medulla.
TMO
It is characterized by special strength and density. It contains a large number of elastic and collagen fibers. The hard shell is formed by dense connective tissue.
Features
The hard shell lines the inside of the cranial cavity. At the same time, it acts as its internal periosteum. In the region of the large opening in the occipital part of the dura mater, it passes into the dura mater of the spinal cord. It also forms the perineural sheaths for the cranial nerves. Penetrating into the holes, the shell fuses with their edges. Communication with the bones of the arch is fragile. The shell is easily separated from them. This causes the possibility of epidural hematomas. In the region of the cranial base, the shell fuses with the bones. In particular, a strong fusion is noted in the areas where the elements are connected to each other and the exit of the cranial nerves from the cavity. The inner surface of the membrane is lined with endothelium. This causes its smoothness and pearlescent shade. In some areas, splitting of the shell is noted. Here its processes are formed. They protrude deeply into the gaps that separate parts of the brain. Triangular canals are formed at the sites of origin of the processes, as well as at the points of attachment to the bones of the internal cranial base. They are also covered with endothelium. These channels are the sinuses of the dura mater.
Sickle
It is considered the largest offshoot of the shell. The sickle penetrates into the longitudinal fissure between the left and right hemispheres without reaching the corpus callosum. It is a thin crescent-shaped plate in the form of 2 sheets. The superior sagittal sinus lies in the split base of the process. The opposite edge of the sickle has a thickening also with two petals. They contain the inferior sagittal sinus.
Connection with elements of the cerebellum
In the front part, the sickle is fused with a cockscomb on the ethmoid bone. The posterior region of the process at the level of the occipital internal protrusion is connected to the tentorium of the cerebellum. He, in turn, hangs over the cranial fossa with a gable tent. It contains the cerebellum. Its insignia penetrates into the transverse fissure in the large brain. Here it separates the cerebellar hemispheres from the occipital lobes. There are irregularities on the front edge of the bait. A notch is formed here, to which the brain stem adjoins in front. The lateral portions of the tenon fuse with the edges of the furrow in the posterior sections on the transverse sinus of the occipital bone and with the upper edges of the pyramids on the temporal bones. The connection extends to the rear processes of the wedge-shaped element in the anterior parts on each side. The cerebellar falx is located in the sagittal plane. Its leading edge is free. It separates the hemispheres of the cerebellum. The back of the sickle is located along the occipital internal crest. It runs to the edge of the large hole and covers it with two legs on both sides. There is an occipital sinus at the base of the sickle.
Other Items
The diaphragm stands out in the Turkish saddle. It is a horizontal plate. There is a hole in its center. The plate is stretched over the pituitary fossa and forms its roof. Below the diaphragm is the pituitary gland. It connects through the hole to the hypothalamus with the help of a funnel and a leg. In the region of the trigeminal depression near the apex of the temporal bone, the dura mater diverges into 2 sheets. They form a cavity in which the nerve node (trigeminal) is located.
Dura sinuses
They are sinuses formed as a result of the splitting of the DM into two sheets. The sinuses of the brain act as a kind of blood vessels. Their walls are formed by plates. The sinuses and veins of the brain have a common feature. Their inner surface is lined with endothelium. Meanwhile, the sinuses of the brain and blood vessels differ directly in the structure of the walls. In the latter, they are elastic and include three layers. When cut, the lumen of the veins subsides. The walls of the sinuses, in turn, are tightly stretched. They are formed by dense fibrous connective tissue, in which elastic fibers are present. When cut, the lumen of the sinuses gapes. In addition, valves are present in the venous vessels. In the cavity of the sinuses there are several incomplete crossbeams and wavy crossbeams. They are covered with endothelium and are thrown from wall to wall. In some sinuses, these elements are significantly developed. There are no muscle elements in the walls of the sinuses. Sinuses of the dura materhave a structure that allows blood to flow freely under the influence of its gravity, regardless of fluctuations in intracranial pressure.
Views
The following sinuses of the dura mater are distinguished:
- Sinus sagittalis superior. The superior sagittal sinus runs along the upper edge of the greater crescent, from the cockscomb to the inner occipital protuberance.
- Sinus sagittalis inferior. The inferior sagittal sinus is located in the thickness of the free edge of the large sickle. It flows into the sinus rectus at the back. The connection is in the area where the lower edge of the large crescent fuses with the anterior edge of the cerebellar tenon.
- Sinus rectus. The direct sine is located in the splitting of the insignia along the line of attachment of a large sickle to it.
- Sinus transversus. The transverse sinus is located at the place where the cerebellum occludes from the brain membrane.
- Sinus occipitalis. The occipital sinus lies at the base of the cerebellar falx.
- Sinus sigmoideus. The sigmoid sinus is located in the sulcus of the same name on the inner cranial surface. It looks like the letter S. In the region of the jugular foramen, the sinus passes into the internal vein.
- Sinus cavernosus. The paired cavernous sinus is located on both sides of the Turkish saddle.
- Sinus sphenoparietalis. The sphenoparietal sinus is adjacent to the posterior free area on the lesser wing of the sphenoid bone.
- Sinus petrosus superior. The superior petrosal sinus is located at the superior edge of the temporal bone.
- Sinuspetrosus inferior. The inferior petrosal sinus is located between the clivus of the occipital and the pyramid of the temporal bones.
Sinus sagittalis superior
In the anterior sections, the superior sinus anastomoses (connects) with the veins of the nasal cavity. The back part flows into the transverse sinus. To the left and to the right of it are lateral gaps communicating with it. They are small cavities located between the outer and inner sheets of DM. Their number and size are very different. The lacunae communicate with the sinus sagittalis superior cavity. They include the vessels of the dura and the brain, as well as the diploic veins.
Sinus rectus
The straight sinus acts as a kind of continuation of the sinus sagittalis inferior from behind. It connects the backs of the superior and inferior sinuses. In addition to the superior sinus, a large vein enters the anterior end of the sinus rectus. Behind the sinus flows into the middle part of the sinus transversus. This section is called the sinus drain.
Sinus transversus
This sinus is the largest and widest. On the inner part of the scales of the occipital bone, it corresponds to a wide furrow. Further sinus transversus passes into the sigmoid sinus. Then he goes to the mouth of the internal jugular vessel. Sinus transversus and Sinus sigmoideus thus act as the main venous collectors. At the same time, all other sinuses flow into the first one. Some venous sinuses enter it directly, some indirectly. On the right and left, the transverse sinus continues into the sinus sigmoideusthe relevant party. The area where the venous sinuses sagittalis, rectus and occipitalis flow into it is called the drain.
Sinus cavernosus
Its other name is cavernous sinus. It received this name in connection with the presence of numerous partitions. They give the sinus an appropriate structure. The abducens, ophthalmic, trochlear, oculomotor nerves, as well as the carotid artery (internal), along with the sympathetic plexus, pass through the cavernous sinus. There is a message between the right and left side of the sinus. It is presented in the form of the posterior and anterior intercavernous sinus. As a result, a vascular ring is formed in the region of the Turkish saddle. Sinus sphenoparietalis flows into the cavernous sinus (into its anterior sections).
Sinus petrosus inferior
It enters the superior bulb of the jugular (internal) vein. The vessels of the labyrinth are also suitable for sinus petrosus inferior. The stony sinuses of the dura mater are connected by several vascular channels. On the basilar surface of the occipital bone, they form the plexus of the same name. It is formed by the fusion of the venous branches of the right and left sinus petrosus inferior. The basilar and internal vertebral choroid plexus connect through the foramen magnum.
Extra
In some areas, the sinuses of the membrane form anastomoses with the external venous vessels of the head with the help of graduates - emissary veins. In addition, the sinuses communicate with diploic branches. These veins are located in the spongy substance in the bones of the cranialvault and flow into the superficial vessels of the head. Blood thus flows through the vascular branches into the sinuses of the dura mater. Then it flows into the left and right jugular (internal) veins. Due to the anastomoses of the sinuses with diploic vessels, graduates and plexuses, blood can flow into the superficial networks of the face.
Vessels
The meningeal (middle) artery (maxillary branch) approaches the hard shell through the left and right spinous foramen. In the temporo-parietal region of the dura mater, it branches. The shell of the anterior fossa of the skull is supplied with blood from the anterior artery (the ethmoid branch of the ophthalmic vessel system). In the dura mater of the posterior fossa of the skull, the posterior meningeal, branches of the vertebral and mastoid branches of the occipital artery branch.
Nerves
The dura is innervated by various branches. In particular, branches of the vagus and trigeminal nerves approach it. In addition, sympathetic fibers provide innervation. They enter the hard shell in the thickness of the outer wall of blood vessels. In the region of the cranial anterior fossa, the DM receives processes from the optic nerve. Its branch, the tentorial, provides innervation to the cerebellar tentorium and the crescent of the brain. The cranial middle fossa is supplied by the meningeal process of the maxillary and part of the mandibular nerves. Most of the branches run along the vessels of the sheath. In the tentorium of the cerebellum, however, the situation is somewhat different. There are few vessels there, and the branches of the nerves are located in it independently of them.
