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The structure of the brain stem briefly. Brain

The brainstem includes the medulla oblongata, pons, midbrain, diencephalon, and cerebellum. The brain stem performs the following functions:

    organizes reflexes that ensure the preparation and implementation of various forms of behavior; 2) carries out a conductive function: through the brain stem there are pathways passing in the ascending and descending directions that connect the structures of the central nervous system; 3) when organizing behavior, it ensures the interaction of its structures with each other, with the spinal cord, basal ganglia and cerebral cortex, i.e. it provides an associative function.

56. Brain stem. The structure of the medulla oblongata and hindbrain.

The medulla oblongata in humans is about 25 mm long. It is a continuation of the spinal cord. Structurally, in terms of the diversity and structure of the nuclei, the medulla oblongata is more complex than the spinal cord. Unlike the spinal cord, it does not have a metameric, repeatable structure; the gray matter in it is not located in the center, but with its nuclei towards the periphery.°

hindbrain is part of the rhombencephalon, formed from rhombomeres 1, 2 and 3. The dorsal part is the cerebellum, cerebellar peduncles (conducting pathways), which intertwine on the ventral side in the form of a massive pons. In the depths of the stem part of the hindbrain lie the nuclei of the cranial nerves, pathways, reticular formation, and suture. In the suture nuclei is the center of falling asleep. In the depth there is a canal - the Sylvian aqueduct.

57. Brain stem. The structure of the midbrain and diencephalon.

P
diencephalon, lies under the corpus callosum and fornix, fused on the sides with the hemispheres of the telencephalon. According to what was said above about the function and development of the forebrain, two main parts are distinguished in the diencephalon:

    dorsal (phylogenetically younger) - thalamencephalon - center of afferent pathways and

    ventral (phylogenetically older) - hypothalamus - the highest vegetative center.

The midbrain, mesencephalon, develops in the process of phylogenesis under the predominant influence of the visual receptor, therefore its most important formations are related to the innervation of the eye. Here, hearing centers were formed, which, together with the centers of vision, later grew in the form of four mounds of the roof of the midbrain.

The human midbrain contains:

    subcortical centers of vision and nuclei of nerves innervating the muscles of the eye;

    subcortical auditory centers;

    all ascending and descending pathways connecting the cerebral cortex with the spinal cord and passing through the midbrain;

    bundles of white matter connecting the midbrain with other parts of the central nervous system.

Accordingly, the midbrain, which is the smallest and most simply structured part of the brain in humans, has two main parts: the roof, where the subcortical centers of hearing and vision are located, and the cerebral peduncles, where the pathways predominantly pass.

58. Spinal cord, its position, structure, functions. Sheaths of the spinal cord.

Spinal cord, lies in the spinal canal and in adults is a long (45 cm in men and 41-42 cm in women), somewhat flattened from front to back cylindrical cord, which at the top (cranially) directly passes into the medulla oblongata, and at the bottom (caudally) ends in a conical point , conus medullaris, at the level of the II lumbar vertebra. Knowledge of this fact is of practical importance (in order not to damage the spinal cord during a lumbar puncture for the purpose of taking cerebrospinal fluid or for the purpose of spinal anesthesia, it is necessary to insert a syringe needle between the spinous processes of the III and IV lumbar vertebrae). From the conus medullaris, the so-called filum terminale extends downward, representing the atrophied lower part of the spinal cord, which below consists of a continuation of the membranes of the spinal cord and is attached to the II coccygeal vertebra.

WITH The spinal cord along its length has two thickenings corresponding to the nerve roots of the upper and lower extremities: the upper one is called the cervical thickening, intumescentia cervicalis, and the lower one is called the lumbosacral thickening, intumescentia lumbosacralis. Of these thickenings, the lumbosacral one is more extensive, but the cervical one is more differentiated, which is associated with a more complex innervation of the hand as an organ of labor

Outdoor, dura mater of the spinal cord separated from the spinal column by the epidural space. The middle, arachnoid, membrane is separated from the hard shell by the subdural space, and from the soft shell by the subarachnoid space. The latter forms below the spinal cord (in the area of ​​the roots of the spinal nerves - the so-called cauda equina) a terminal ventricle filled with cerebrospinal fluid.

The human brain is the most complex of all organs. The number of functions performed by the brain is surprisingly large. The brain consists of a brainstem, two hemispheres and the cerebellum. The trunk is extremely important, which is responsible for many functions of the body. This structure is a connecting element that connects the brain and spinal cord. All vital human systems require full functioning of the brainstem. Fortunately, the brain stem has been well studied, and all the mechanisms of its operation are already fully understood.

What is the brain?

Human brain- an organ that is the center of the entire nervous system. In total, it contains more than 20 billion neurons that transmit information to the necessary centers of the human body. Signal transmission is carried out by an electrical impulse. All parts of the brain are responsible for their specific capabilities and functions. There are 5 departments in total:

  1. oblong;
  2. finite;
  3. intermediate;
  4. rear;
  5. average.

The brain also includes: thalamus, hypothalamus, pituitary gland, pons, cerebellar cortex and vermis with nuclei, cerebral cortex, basal ganglia.

The brain has a naturally formed defense. The brain's protection consists of three membranes: soft, hard and cobwebby. But the main element that is responsible for the safety of the organ is cranium.

The medulla oblongata is a continuation of the spinal cord. It contains two substances: white and gray. White is the information transmission channels, gray is the nerve nuclei.

The oblong part passes into the Valoriev Bridge. It includes nerve fibers and gray matter. The blood artery supplying the brain passes through this part. The pons continues into the cerebellum, another important section.

Cerebellum- the central link in the brain system. It consists of two small hemispheres covered with white and gray matter. The most multifunctional part of the brain.

The midbrain is connected to the cerebellum by two legs. The structure of the trunk is directly related to the location and access to other departments. The middle section has 4 tubercles (2 visual and 2 auditory). The brain communicates with the spinal cord through nerve fibers that arise from the tubercles.

The two large hemispheres are completely covered with cortex. It is in this cortex that all processes associated with thinking take place. Between the hemispheres is the corpus callosum, which connects them. Each hemisphere is divided into lobes of the forehead, temples, crown and occiput.

The brain stem is responsible for reticular information. It is the connecting link between the brain and spinal cord. The department is quite interesting, which has motivated multiple studies.

What are reflexes? How is breathing regulated when a person sleeps? Why does the pupil move? How does a person feel and distinguish tastes? These and many other questions forced us to carefully examine such a part of the brain as the brainstem.

How and why was the brain stem formed?


All the functions of the stem department have long been defined. His research is carried out by neurophysiologists, anatomists and other doctors. The basis for the emergence of a full-fledged trunk was the medulla oblongata. Brain stem– a very complex system in which many processes occur simultaneously.

The first creatures that came onto land had only a medulla oblongata, which allowed them to be guided by primitive instincts. During evolution, it was necessary to improve reflexes, reactions and thinking. The big brain appeared much later, when animals already had thinking. After the appearance of erect man, the cerebellum formed in the cranium. And with subsequent generations, the brain acquired more and more convolutions, cortex, nerve nuclei and other elements that are characteristic of modern man.

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Now the main tasks of the trunk are to ensure breathing and blood circulation, and their regulation. The structure fully supports human life, so pathologies are extremely dangerous. Cerebral edema is quite dangerous. In this case, the barrel moves lower, where it is clamped in the occipital foramen. Then full functioning is impossible, which causes a lot of consequences.

Structure


The structure of the brain stem consists of 3 main elements. The midbrain is formed by the peduncles and quadrigeminal. Gives off 3rd and 4th pairs of nerves.

The Varoliev bridge is more compacted. Located in the middle part. Formed by the base, quadrigeminal, tegmentum and various elements of the cranial ventricle system. Gives off from 5th to 8th pairs of nerves.

The largest part is the medulla oblongata. A special groove will separate the oblong part from the bridge. Gives off the 9th to 12th pairs of nerves and one nucleus of the 7th pair.

The brainstem also includes nerve cells with nuclei, which are called the reticular formation of the brainstem. Such formations have two types of neutrons in their structure: dendrites and axons. The first ones do not have many branches. Axons have T-shaped branching. Together they create a network called the reticulum. This is where the term reticular formation came from. They are directly connected to the central nervous system, directing and transmitting information to other processing centers. Information may have an afferent type of conduction, or efferent. The afferent type directs signals to the formation, the efferent type – from it.

The functions performed directly depend on the structure of the department.

Functions

The brain stem can implement vital functions thanks to the following cranial nerve nuclei:

  1. motor. Directs the functionality of the muscles of the eyelids and eyes. Also controls reflexes of the eyelids and eyeball. Directs the work of the chewing muscles;
  2. sensitive. They participate in the work of all reflexes associated with digestion - from swallowing to the gag reflex. Taste buds work thanks to the sensory nuclei. Also responsible for sneezing;
  3. parasympathetic. The movement and size of the pupil depends on the command from a given core. Also monitors the ciliary muscle. Another name is the trochlear nerve nucleus;
  4. upper salivary. Controls the functioning of the salivary glands. Responsible for the timely and sufficient release of oral fluid and saliva;
  5. vestibular. They control and direct the work of the vestibular apparatus, which is responsible for the balance of the body;
  6. double. One nucleus that completely controls the swallowing reflex. Sensory nuclei also help with function;
  7. cochlear. Two nuclei that are responsible for hearing receptors. They transmit signals to the center related to the cerebellum.

That is, the brain stem helps a person move, think, hear, see, touch and other capabilities necessary for full life. In addition to such capabilities, it controls all head reflexes. The trunk processes the impulses it receives from the central nervous system and gives commands to the organs through the spinal cord.

Chain reflexes


Chain reflexes also occur in the brainstem. This happens if several pairs of cores are activated simultaneously.

Oculomotor reflexes coordinate gaze. The impulse is transmitted through the cochlear and ternary nerves to the nuclei. The direction of gaze involves the oculomotor, lateral and abducens nerves. The process is monitored by the reticular formations, the cerebellum and the cerebral cortex.

The act of chewing occurs due to contractions of the extensor muscles of the lower jaw. The impulse is transmitted along the ternary nerve. In the medulla oblongata near the pons there is a center that is responsible for the entire chewing process. Afferent signals excite the motor neurons of the masticatory muscles, which raise and lower the movable jaw.

The act of swallowing moves food that has entered the oral cavity into the digestive tract. First, the receptors of the tongue root are excited, then the palate. When food is already in the throat, receptors in the pharynx are activated, which help direct food into the esophagus. This act is ensured by the swallowing center, which is connected to the respiratory center.

Cough– a protective reaction of the human body to irritation in the trachea, larynx or bronchi. The vagus nerve carries an impulse to the cough center. The nucleus is located in the medulla oblongata and is directly connected to the respiratory center. First, take a deep breath. The glottis is closed and the expiratory muscles contract to exhale. This creates high pressure, followed by a sharp exhalation when the glottis opens. The air flow passes exclusively through the mouth.

The sneeze reflex is also protective. In the mucous membrane of the nasal cavity, irritation of the ternary nerve occurs. The sneezing center is located near the cough. The whole process happens the same way, only the air flow comes out not through the mouth, but through the nose.

Tumors of the trunk. Types and treatment


There are 10 types of brain stem tumors:

  • Primary. Occur when tissue is damaged;
  • Secondary. May occur after tuberculosis, severe flu or other dangerous diseases;
  • Parastem. They grow closely with the trunk and gradually deform it;
  • Cerebellar. The cerebellar peduncles are affected first. Then it gradually spreads to the stem part;
  • Exophytic. They also arise in the cerebellum, after which they spread to the trunk. May form in the membrane of the cranial ventricle;
  • Diamond-shaped. They arise in the occipital part where the depression of the same name is located;
  • Deforming. They form directly on the trunk or on other parts. They change the shape of the stem part, which greatly affects the performance of the department;
  • Diffuse. Unfortunately, they are almost impossible to treat. It is extremely difficult to determine the boundaries of the tumor. It fuses too much with the brain matter.

Diagnosis of tumors


It can be almost impossible to suspect the formation of tumors. Some immediately show obvious signs of presence, others can develop for a long time without causing any inconvenience.

The first step is anamnesis analysis. After examining the results, the doctor may order the next test. In a healthy brain, functions should be performed without errors. Therefore, studies are being carried out on the functionality of the nerves of the head.

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You can also perform instrumental diagnostics. The formation can be confirmed by electroencephalography, rheoncephalography or puncture. Research confirms the diagnosis 100%. Instrumental diagnostics allows you to obtain data on the activity of different parts of the trunk.

Modern methods are magnetic resonance imaging (MRI) and computed tomography (CT). Studies visualize formations, which makes it possible to determine the exact size. Studies can also suggest the histological features of the tumor.

Treatment of tumors


The prognosis for the outcome of treatment depends primarily on the type of tumor. Its location and size also play a big role. The most difficult tumors to treat are those that have formed inside the trunk.

Benign formations can be easily removed surgically. There may be exceptions if a surgical knife, entering a foreign body, can damage the brain stem structures. Before and after the operation, the doctor prescribes laser and chemotherapy. They prevent the growth of glioma. They also remove cancer cells that remain after surgical removal and prevent their development.

But patients who develop malignancy account for about 80%. Such tumors cannot be removed by surgery. A popular alternative method is radiation therapy. The tumor is exposed to radioactive radiation. But the method cannot completely kill cancer cells. Therefore, they are used to stop the development of a tumor or avoid relapse.

Modern methods of treatment


If a brainstem pathology is detected, then part of the brain cannot fully decipher the information due to deformation or damage, which can cause atrophy of some organs. Therefore, stereotactic therapy is often used, which can also quickly cope with pathology.

This therapy is a combination of two radiations: “Cyber ​​Knife” and “Gamma Knife”. A computer that is turned on emits radiation, the type and dose of which it determines independently. This method is called “Cyber ​​Knife”. The second method is radiological radiation. Gamma Knife is performed by placing a special helmet on the head that emits waves and particles.

Another treatment option is chemotherapy. Cytostatic drugs stop development, after which the formations are removed. For greater effectiveness, the doctor often prescribes a combination of therapies. Some are larger scale, some are more precise. The brain stem is a hard-to-reach part of the main organ of the central nervous system. Therefore, combining procedures can give excellent results.

Brain stem stroke


Problems of the cardiovascular system always have strong consequences. Blood flow in the area of ​​the stem part, there may be vascular damage due to cerebral infarction. What is an ischemic stroke? This is by far the most dangerous stroke. Brain cells are severely damaged due to poor circulation. Many diseases can lead to the development of such a disease. Hemorrhagic stroke is less dangerous, but destructive to brain tissue.

Brain stem

Brain oblongata. The medulla oblongata begins from the spinal cord, maintaining its shape. Their border is the level of the lower edge of the first cervical vertebra. With its upper widened end it passes into the pons. The border between them is a transverse groove at the lower edge of the pons. On its front surface, on both sides of the longitudinal slit, there are two rollers called pyramids.

The fibers of the lower section of the right pyramid pass to the left side, and the left - to the right. This fiber transition is called the intersection of the pyramids. Thanks to the decussation, the cortex of the right hemisphere controls the functions of the left side of the body and the left limbs, and, on the contrary, the left hemisphere controls the functions of the right side and right limbs.

Visible on the dorsal surface of the medulla oblongata diamond pit- the bottom of the fourth cerebral ventricle, on which are the nuclei of eight pairs of twelve nerves extending from the brain.

Sections of the medulla oblongata show white and gray matter. In the lower section, the gray matter still retains the appearance of a butterfly, and in the upper section it is in the form of separate sections (nuclei) located along the posterior surface. These are the centers of respiration, regulation of cardiac activity, vasomotor, metabolism, sucking, swallowing and others.

White matter consists of centripetal and centrifugal pathways.

Like the spinal cord, with which it is similar in structure, the medulla oblongata performs two functions: reflex and conduction. Associated with it are reflexes of body position and changes in the tone of the neck and trunk muscles.

Pons. The pons is a roll-shaped, white formation lying transversely above the medulla oblongata.

The bulk of the pons is white matter, formed by nerve fibers in the transverse direction. Gray matter is distributed in the thickness of white matter in separate nuclei. These are clusters of neuron bodies with outgoing processes.

The white matter of the pons is the conducting pathways. They connect the cerebral cortex with peripheral organs.

Cerebellum. The cerebellum is located in the skull, below and behind the cerebral hemispheres, above the medulla oblongata and the pons. By the age of 10, his weight increases 6 times and is 129-133 G with an adult's weight being slightly more than 150 ᴦ.

The cerebellum has two hemispheres. They are covered with a thin layer of gray matter. The white matter contains gray matter nuclei: jagged, spherical and others. The cerebellum is connected to other parts of the brain by three pairs of peduncles. The strongest, middle cerebellar peduncles connect it to the pons. The anterior peduncles connect the cerebellum to the quadrigeminal region. The hind legs (rope bodies) connect the cerebellum to the medulla oblongata. Along these legs, centripetal fibers from the spinal cord and vestibular apparatus enter the cerebellum.

Functionally, the cerebellum is involved in every motor act - it provides a certain tension to muscle groups and eliminates unnecessary and unnecessary movements. It has no effect on blood circulation, breathing, metabolism, etc.

A disorder in the activity of the cerebellum in humans leads to impaired coordination of movements and distribution of muscle tone between individual muscle groups of the limbs, and to a decrease in tone. At the same time, movements become awkward and uncalculated. A person quickly gets tired, walks with his legs wide apart, continuously sways, stumbles and falls. Subsequently, the movement disorder is restored, but not completely. This recovery is explained by the participation of the cerebral cortex in the coordination of movements.

Middle brain. The midbrain consists of cerebral peduncles, quadrigeminal and a channel called Sylvian aqueduct. It is located above the pons.

In the upper pair of quadrigeminal tubercles there are intermediate centers of orienting reflexes of vision, and in the lower ones - of hearing.

The anterior surface of the midbrain is represented by two voluminous bundles - the cerebral peduncles. These are pathways to the cerebral hemispheres. Inside the midbrain there are small accumulations of gray matter - the nuclei of the trochlear and oculomotor nerves.

Intermediate brain. Above the midbrain lies the diencephalon. It consists of two visual cusps And subtubercular region. Between the visual thalamus there is a cavity of the third ventricle of the brain.

Visual tuberosities- paired formation visible on longitudinal and transverse sections of the hemispheres. All centripetal impulses from the body's receptors, except auditory ones, enter the visual thalamus, where they transfer to a new neuron and are directed to the cerebral cortex. Damage to the visual tuberosities causes complete or partial loss of sensitivity, headaches, sleep disorders, paralysis and decreased vision.

Subcutaneous region presented gray lump, funnel And pituitary gland- inferior cerebral appendage. Anterior to the subtubercular region, the optic nerves cross.

The formation and differentiation of the various nuclei of the subthalamic region are completed non-simultaneously. By the age of 7, cell differentiation ends, and during puberty, the connections of the subthalamic region with other parts of the brain and body systems rapidly grow.

The subtubercular region is functionally associated with the regulation of the metabolism of proteins, fats, salts and water. It is in charge of the work of internal organs (intestinal peristalsis, contraction of the uterus in women, the bladder, the walls of blood vessels), sweating, carbohydrate metabolism, regulation of heat exchange in the body, regulation of sleep and wakefulness.

Reticular formation of the brain. Mesh or reticular brain formation is a set of structural elements located in the central parts of the brain stem.

Neurons of the reticular formation differ in their structure from all other neurons. Their dendrites are weakly branched, and axons, on the contrary, come into contact with a huge number of nerve cells. The nerve fibers of the formation go in a variety of directions. And when viewed under a microscope, they look like a grid, which is the basis for the name mesh formation.

The cells of the reticular formation have different sizes and shapes. Its magnocellular neurons are located so that their dendrites and lateral processes of axons (collaterals) branch in a plane perpendicular to the longitudinal axis of the brain stem.

In some places, the cells of the reticular formation are scattered in the brain stem, and sometimes grouped into nuclei (for example, the nucleus in the tegmentum of the pons). The cells of the formation are located along the entire length of the brain stem and occupy a central position from the medulla oblongata to the optic thalamus inclusive.

The reticular formation is connected to all parts of the central nervous system, including the cerebral cortex.

The reticular formation is considered an “energy generator” that regulates processes occurring in other parts of the central nervous system, including the cerebral cortex.

All complex reflex acts that require the participation of many muscles in different combinations (articulation of sounds, breathing, vomiting, sneezing, etc.) are coordinated in a reticular formation. In this case, it itself is a complex reflex center, ensuring the relative safety of the automaticity of breathing and cardiac activity.

The reticular formation has a general nonspecific activating effect on the entire cerebral cortex. This is ensured by the presence of ascending pathways from the formation to all lobes of the cerebral hemispheres. Two afferent systems pass through the brain stem to the cortex: one is specific (sensitive pathways from all types of receptors); the other is nonspecific, formed by a reticular formation. The first system ends in the cell bodies of the fourth layer of the cortex, and the second - on the dendrites of all layers of the cerebral cortex. The interaction of both systems determines the final reaction of neurons in the cerebral cortex.

The functional interaction of the reticular formation with the cerebral cortex does not take place without the participation of humoral regulation, which ensures the analysis and synthesis of nerve impulses entering the cortex along the afferent (ascending) pathways.

Brainstem - concept and types. Classification and features of the category “Brain stem” 2017, 2018.

The brain stem is phylogenetically the most ancient part of the brain. It is closely connected with the spinal cord and the cerebral hemispheres of the telencephalon. This is where the vital functions of the body are located.

The brain stem includes the medulla oblongata, medullary pons, midbrain and diencephalon.

Medulla oblongata (medulla oblongata, myelencephalon) is a direct continuation of the spinal cord. The border between the medulla oblongata and the spinal cord corresponds to the level of the edges of the foramen magnum. The upper border of the medulla oblongata on the ventral surface runs along the posterior edge of the pons. The anterior sections of the medulla oblongata become somewhat thicker compared to the posterior ones, and this section of the brain takes the shape of a truncated cone or onion, for its similarity it is also called an onion. The length of the medulla oblongata of an adult is on average 25 mm.

In the medulla oblongata, there are ventral, dorsal and two lateral surfaces, which are separated by grooves (Fig. 11.18). The sulci of the medulla oblongata are a continuation of the sulci of the spinal cord and have the same names: anterior median fissure, posterior median sulcus, anterolateral and posterolateral sulci.

Rice. 11.18. Brain stem

On both sides of the anterior median fissure on the ventral surface of the medulla oblongata there are convex, gradually tapering downwards pyramids. The bundles of fibers that make up the pyramids move to the opposite side and enter the lateral cords of the spinal cord, i.e. there is a cross of pyramids . The decussation also serves as the anatomical boundary between the medulla oblongata and the spinal cord.

Lateral to the pyramid on both sides there are oval elevations - olives(formed by the inferior olivary, medial and posterior accessory yars), which is separated from the pyramid by the anterolateral groove (Fig. 11.19). Between the lower olive nuclei there is the so-called interolive layer, represented by internal arcuate fibers - processes of cells lying in the thin and wedge-shaped nuclei. These fibers form the medial lemniscus, the fibers of which belong to the proprioceptive pathway of the cortical direction. In the anterolateral groove, the roots of the hypoglossal nerve (XII pair) emerge from the medulla oblongata. Slightly above which is located the reticular formation, formed by the interweaving of nerve fibers and the nerve cells lying between them and their clusters in the form of small nuclei. In addition to regulating the excitability and tone of various parts of the central nervous system, the reticular formation ensures the readiness of the centers for activity, enhances or inhibits the reflex activity of the spinal cord.



Rice. 11.19. Cross section of the medulla oblongata (at two levels).

On the dorsal surface on the sides of the posterior median sulcus, the thin and wedge-shaped bundles of the posterior funiculi of the spinal cord end with thickenings, forming the tubercles of the thin and wedge-shaped nuclei (Gaull and Burdach nuclei). Dorsal to the olive, the roots of the glossopharyngeal, vagus and accessory nerves (IX, X and XI pairs) emerge from the posterolateral groove of the medulla oblongata - the retroolive groove.

The dorsal part of the lateral funiculus widens slightly upward. Here it is joined by fibers extending from the wedge-shaped and tender nuclei. Together they form the inferior cerebellar peduncle. The surface of the medulla oblongata, bounded below and laterally by the inferior cerebellar peduncles, participates in the formation of the rhomboid fossa, which is the bottom of the fourth ventricle.

At the level of the medulla oblongata there are vital centers such as respiratory and circulatory centers. In addition, at the level of the medulla oblongata, food reflexes occur (swallowing, sucking, secretory and contractile activity of the digestive tract); protective reflexes (coughing, sneezing, lacrimation, vomiting); reflexes associated with the position of the head and body in space, etc.

Fourth (IV) ventricle (ventriculus quartus) is a derivative of the cavity of the rhombencephalon. The medulla oblongata, pons, cerebellum and isthmus of the rhombencephalon take part in the formation of the walls of the fourth ventricle. The shape of the cavity of the IV ventricle resembles a tent, the bottom of which has the shape of a rhombus (diamond-shaped fossa) and is formed by the posterior (dorsal) surfaces of the medulla oblongata and the pons. The border between the medulla oblongata and the pons on the surface of the rhomboid fossa is the medullary stripes (IV ventricle).

The roof of the IV ventricle in the form of a tent hangs over the rhomboid fossa. The superior cerebellar peduncles and the superior medullary velum stretched between them take part in the formation of the anterosuperior wall of the tent. The lateral inferior wall is made up of the inferior medullary velum, which is attached to the legs of the flocculus on the sides. From the inside, adjacent to the inferior medullary velum, represented by a thin epithelial plate (the remnant of the dorsal wall of the third cerebral vesicle of the rhombencephalon), is the vascular base of the fourth ventricle, covered on the side of the cavity of the fourth ventricle with an epithelial plate, forming the choroid plexus of the fourth ventricle

Diamond fossa (fossa rhomboidea) It is a diamond-shaped depression, the long axis of which is directed along the brain. It is bounded laterally in its upper section by the superior cerebellar peduncles, and in the lower section by the inferior cerebellar peduncles. In the posteroinferior corner of the rhomboid fossa, under the lower edge of the roof of the IV ventricle, under the valve there is an entrance to the central canal of the spinal cord. In the anterosuperior corner there is a hole leading into the midbrain aqueduct, through which the cavity of the third ventricle communicates with the fourth ventricle. The lateral corners of the rhomboid fossa form the lateral recesses. In the median plane, along the entire surface of the rhomboid fossa, from its upper to lower corner, a shallow median groove extends. On the sides of this groove there is a paired medial elevation, limited on the lateral side by the border groove. In the upper parts of the eminence related to the pons, there is a facial tubercle, corresponding to the nucleus of the abducens nerve (VI pair) located in this place in the thickness of the brain and the genus of the facial nerve that encircles it, the nucleus of which lies somewhat deeper and more lateral. The anterior (cranial) sections of the border sulcus, somewhat deepening and widening upward (anteriorly), form the superior (cranial) fossa. The posterior (caudal, lower) end of this groove continues into the lower (caudal) fossa, barely visible on preparations.

Brain Bridge (ponts, pons) at the base of the brainstem has the appearance of a transversely located ridge, which at the top (in front) borders the midbrain (with the cerebral peduncles), and at the bottom (back) - with the medulla oblongata.

The dorsal surface of the bridge faces the fourth ventricle and participates in the formation of its bottom rhomboid fossa. In the lateral direction, on each side, the bridge narrows and passes into the middle cerebellar peduncle, which extends into the cerebellar hemisphere. The border between the middle cerebellar peduncle and the pons is the exit point of the trigeminal nerve. In the deep transverse groove separating the pons from the pyramids of the medulla oblongata, the roots of the right and left abducens nerves emerge. In the lateral part of this groove the roots of the facial (VII pair) and vestibulocochlear (VIII pair) nerves are visible.

On the ventral surface of the pons, which is adjacent to the clivus in the cranial cavity, a wide but shallow basilar (main) groove is noticeable. The artery of the same name lies in this groove. of the brain by the lateral groove. In the area of ​​the triangle, in its depth, the fibers of the lateral (supra) loop lie.

In the central sections of the bridge section, a thick bundle of fibers is noticeable, running transversely and belonging to the conduction path of the auditory analyzer - the trapezoidal body, which divides the bridge into the posterior part (tegmentum of the bridge) and the anterior (basilar) part. Between the fibers of the trapezoid body are the anterior and posterior nuclei of the trapezoid body. In the anterior (basilar) part of the bridge, longitudinal and transverse fibers are visible. The longitudinal fibers of the bridge belong to the pyramidal tract (cortical-nuclear fibers). There are also cortical-pontine fibers that end on the nuclei (owner) of the bridge, located between groups of fibers in the thickness of the bridge. The processes of the nerve cells of the pons nuclei form bundles across the fibers of the pons, which are directed towards the cerebellum, forming the middle cerebellar peduncles.

In the posterior (dorsal) part (tegmentum pons), in addition to the fibers of the ascending direction, which are a continuation of the sensitive pathways of the medulla oblongata, there are focal accumulations of gray matter - the nuclei of the V, VI, VII, VIII pairs of cranial nerves, providing eye movements, facial expressions, and activity auditory and vestibular apparatus; the nuclei of the reticular formation and the proper nuclei of the bridge, which are involved in connections between the cerebral cortex and the cerebellum and transmit impulses from one part of the brain to another.. Above the trapezoidal body, closer to the median plane, is the reticular formation, and even higher is the posterior longitudinal fasciculus.

In the brain stem, the next section after the pons, small but functionally important, is isthmus of the rhombencephalon, consisting of the superior cerebellar peduncles, the superior medullary velum and the triangular loop, in which the fibers of the lateral (auditory) lemniscus pass.

Midbrain (mesencephalon) consists of a dorsal section - the roof of the midbrain and a ventral section - the cerebral peduncles, which are delimited by a cavity - the aqueduct of the brain. The lower border of the midbrain on its ventral surface is the anterior edge of the pons, the superior optic tract and the level of the mammillary bodies. On the dorsal surface, the upper (anterior) border of the midbrain corresponds to the posterior edges (surfaces) of the thalami, the posterior (lower) border corresponds to the level of exit of the roots of the trochlear nerve (IV pair).

On a brain specimen, the lamina tetracholomius, or the roof of the midbrain, can be seen only after the cerebral hemispheres have been removed.

The roof of the midbrain (plate quadrigeminal) is located above the cerebral aqueduct and consists of four elevations - hillocks, shaped like hemispheres, separated from each other by two grooves intersecting at right angles. The longitudinal groove is located in the median plane and in its upper (anterior) sections forms a bed for the pineal gland, and in the lower sections it serves as the place from which the frenulum of the superior medullary velum begins. A transverse groove separates the superior colliculi from the inferior. From each of the mounds, thickenings in the form of a roller extend in the lateral direction - the handle of the mound. The handle of the superior colliculus goes to the lateral geniculate body, the handle of the inferior colliculus goes to the medial geniculate body. In humans, the superior colliculus and lateral geniculate body perform the function of subcortical visual centers. The inferior colliculus and medial geniculate body are subcortical auditory centers.

The cerebral peduncles are clearly visible at the base of the brain in the form of two thick white, longitudinally striated ridges that emerge from the pons, go forward and laterally (diverge at an acute angle) to the right and left hemispheres of the cerebrum. The depression between the right and left cerebral peduncles is called the interpeduncular fossa. The bottom of this fossa serves as a place where blood vessels penetrate the brain tissue. After removal of the choroid on brain preparations, a large number of small holes remain in the plate forming the bottom of the interpeduncular fossa; hence the name of this gray plate with holes - posterior perforated substance. On the medial surface of each cerebral peduncle there is a longitudinal oculomotor groove, from which the roots of the oculomotor nerve (III pair) emerge.

On a cross-section of the midbrain, the substantia nigra (substantia nigra) is clearly visible in the cerebral peduncle with its dark color (due to the melanin pigment contained in nerve cells), which divides the cerebral peduncle into two sections: the posterior (dorsal) - operculum, and the anterior (ventral) department - the base of the cerebral peduncle (Fig. 11.20). The midbrain nuclei lie in the tegmentum and ascending pathways pass through. The base of the cerebral peduncle consists entirely of white matter, and descending pathways pass here.

Rice. 11.20. Cross sections of the midbrain at the level of the inferior and superior colliculi.

The aqueduct of the midbrain (Aqueduct of Sylvius) is a narrow canal about 1.5 cm long; connects the cavity of the third ventricle with the fourth and contains cerebrospinal fluid. Around the midbrain aqueduct there is a central gray matter, in which the nuclei of two pairs of cranial nerves are located in the area of ​​the bottom of the aqueduct. At the level of the superior colliculi, near the midline, there is a paired nucleus of the oculomotor nerve. It takes part in the innervation of the eye muscles. Ventral to it is the parasympathetic nucleus of the autonomic nervous system - the accessory nucleus of the oculomotor nerve (Yakubovich nucleus, Westphal-Edinger nucleus). Fibers arising from the accessory nucleus innervate the smooth muscles of the eyeball (the muscle that constricts the pupil and the ciliary muscle). Anterior and slightly above the nucleus of the third pair is one of the nuclei of the reticular formation - the intermediate nucleus. The processes of the cells of this nucleus participate in the formation of the reticulospinal tract and the posterior longitudinal fasciculus.

At the level of the inferior colliculi in the ventral sections of the central gray matter lies the paired nucleus of the IV pair - the nucleus of the trochlear nerve. In the lateral parts of the central gray matter throughout the entire midbrain there is the nucleus of the midbrain tract of the trigeminal nerve (V pair).

In the tegmentum, the largest and most noticeable on a transverse section of the midbrain is the red nucleus; it is located slightly above (dorsally) the substantia nigra, has an elongated shape and extends from the level of the inferior colliculus to the thalamus. Lateral and above the red nucleus in the tegmentum of the cerebral peduncle, a bundle of fibers that are part of the medial lemniscus is visible in the frontal section. Between the medial lemniscus and the central gray matter is the reticular formation. The base of the cerebral peduncle is formed by descending pathways. The inner and outer sections of the base of the cerebral peduncles form the fibers of the corticopontine tract.

The nerve fibers that make up the medial lemniscus are processes of the second neurons of the proprioceptive sensitivity pathways. The tegmentum of the midbrain contains fibers from the sensory nuclei of the trigeminal nerve, called the trigeminal lemniscus.

The processes of nerve cells of some nuclei form tegmental decussations in the midbrain (the dorsal decussation of the tegmentum belongs to the fibers of the tegmental spinal tract; the ventral decussation of the tegmentum belongs to the fibers of the red nucleus-spinal tract).

Diencephalon (diencephalon) entirely hidden under the cerebral hemispheres. Only at the base of the brain can one see the central part of the diencephalon - the hypothalamus.

The gray matter of the diencephalon consists of nuclei belonging to the subcortical centers of all types of sensitivity. The diencephalon contains the reticular formation, centers of the extrapyramidal system, vegetative centers (regulate all types of metabolism), and neurosecretory nuclei.

The white matter of the diencephalon is represented by pathways of ascending and descending directions, providing bilateral communication of subcortical formations with the cerebral cortex and nuclei of the spinal cord. In addition, the diencephalon includes two endocrine glands - the pituitary gland, which takes part together with the corresponding nuclei of the hypothalamus in the formation of the hypothalamic-pituitary system, and the pineal gland of the brain.

The boundaries of the diencephalon at the base of the brain are posteriorly - the anterior edge of the posterior perforated substance and the optic tracts, and anteriorly - the anterior surface of the optic chiasm.

The diencephalon includes the following sections: thalamic region (area of ​​the visual thalamus, visual brain), which is located in the dorsal areas; the hypothalamus, which unites the ventral parts of the diencephalon; III ventricle (Fig. 11.21).

TO thalamic region include the thalamus, metathalamus and epithalamus.

Thalamus(posterior thalamus, thalamus, thalamus dorsalis) – paired formation, located on both sides of the third ventricle. In the anterior section, the thalamus narrows and ends with the anterior tubercle; the posterior end is thickened and called the cushion.

The medial surfaces of the posterior thalami of the right and left are connected to each other by interthalamic fusion. The lateral surface of the thalamus is adjacent to the internal capsule. Inferiorly and posteriorly it borders with the tegmentum of the midbrain peduncle.

The thalamus consists of gray matter, in which individual clusters of nerve cells are distinguished - the nuclei of the thalamus. Currently, there are up to 40 cores that perform various functions. The main nuclei of the thalamus are anterior, medial, and posterior. Some of the processes of thalamic neurons are directed to the nuclei of the striatum of the telencephalon (in this regard, the thalamus is considered as a sensitive center of the extrapyramidal system), and some - thalamocortical bundles - to the cerebral cortex. Below the thalamus is the so-called subthalamic region, which continues downward into the tegmentum of the cerebral peduncle. This is a small area of ​​the medulla, separated from the thalamus on the side of the third ventricle by the hypothalamic groove. The red nucleus and substantia nigra of the midbrain continue into the subthalamic region from the midbrain and end there. To the side of the substantia nigra is the subthalamic nucleus (corpus lewis).

Metathalamus(zathalamic region, metathalamus) represented by the lateral and medial geniculate bodies. These are oblong-oval bodies connected to the colliculi of the roof of the midbrain with the help of the handles of the superior and inferior colliculi. The lateral geniculate bodies, together with the superior colliculi of the midbrain, are subcortical centers of vision. The medial geniculate body and the inferior colliculus of the midbrain form the subcortical hearing centers.

Epithalamus(suprathalamic region, epithalamus) includes the pineal gland, which, with the help of leashes, connects to the medial surfaces of the right and left thalamus. The anterior sections of the leashes form a commissure of the leashes before entering the pineal gland. Front and below the pineal body there is a bundle of transversely running fibers - the epithalamic commissure.

Hypothalamus(hypothalamus) forms the lower parts of the diencephalon and participates in the formation of the floor of the third ventricle. The hypothalamus includes the optic chiasm, optic tract, gray tubercle with infundibulum, and mammillary bodies (Fig. 11.22).

Optic chiasm (chiasms opticum) has the appearance of a transversely lying ridge formed by fibers of the optic nerves (II pair of cranial nerves), partially passing to the opposite side (forming a decussation). On each side, this ridge continues laterally and posteriorly into the optic tract, which ends with two roots in the subcortical centers of vision (the lateral geniculate body and the superior colliculus of the midbrain roof). The terminal lamina, which belongs to the telencephalon, is adjacent to the anterior surface of the optic chiasm and fuses with it. It consists of a thin layer of gray matter, which in the lateral parts of the plate continues into the substance of the frontal lobes of the hemispheres.

Posterior to the optic chiasm is gray bump (tuber cinereum) behind which lie the mastoid bodies, and on the sides are the optic tracts. Below, the gray mound turns into a funnel , which connects to the pituitary gland. The walls of the gray tuberosity are formed by a thin plate of gray matter containing gray tuberous nuclei.

Mastoid bodies (corpora mamillaria) located between the gray tubercle in front and the posterior perforated substance in the back. They look like two small, about 0.5 cm in diameter each, white spherical formations. The white matter is located only on the outside of the mastoid body. Inside there is gray matter, which secretes medial and lateral nuclei of the mastoid body

In the hypothalamus, there are three main hypothalamic areas of accumulation of groups of nerve cells of different shapes and sizes: anterior, intermediate and posterior. Clusters of nerve cells in these areas form more than 30 nuclei of the hypothalamus.

Nerve cells of the nuclei of the hypothalamus have the ability to produce secretion (neurosecretion), which can be transported through the processes of these same cells to the pituitary gland. Such nuclei are called neurosecretory nuclei of the hypothalamus. In the anterior region of the hypothalamus there are the supraoptic (supraoptic) and paraventricular nuclei. The processes of the cells of these nuclei form the hypothalamic-pituitary bundle, ending in the posterior lobe of the pituitary gland. Among the group of nuclei of the posterior region of the hypothalamus, the largest are the medial and lateral nuclei of the mastoid body, and the posterior hypothalamic nucleus . The group of nuclei of the intermediate hypothalamic region includes: inferior medial and superior medial hypothalamic nuclei, dorsal hypothalamic nucleus etc.

The nuclei of the hypothalamus are connected by a rather complex system of afferent and efferent pathways. Therefore, the hypothalamus has a regulatory effect on numerous autonomic functions of the body. The neurosecretion of the hypothalamic nuclei can influence the functions of the glandular cells of the pituitary gland, enhancing or inhibiting the secretion of a number of hormones, which in turn regulate the activity of other endocrine glands.

The presence of nervous and humoral connections between the hypothalamic nuclei and the pituitary gland made it possible to combine them into the hypothalamic-pituitary system.

Third (III) ventricle (ventriculus tertlus) occupies a central position in the diencephalon. The lower wall, or bottom of the third ventricle, is the hypothalamus. In the lower wall there are two protrusions (depressions) of the cavity of the third ventricle: the infundibulum and the optic recess.

The anterior wall of the third ventricle is formed by the terminal plate, columns of the fornix and anterior commissure. On each side, the column of the fornix in front and the anterior part of the thalamus in the back limit the interventricular foramen.

The posterior wall of the third ventricle is the epithalamic commissure, under which is the opening of the cerebral aqueduct. All walls of the third ventricle from the inside, from the side of its cavity, are lined with ependyma. The upper wall is formed by a vascular base, which is represented by a soft (vascular) membrane (the roof of the third ventricle itself), which penetrates into the third ventricle in two layers under the splenium of the corpus callosum and the fornix.