The ventral part is made up of massive cerebral peduncles, the main part of which is occupied by the pyramidal tracts. between the legs there is an interpeduncular fossa, fossa interpeduncularis, from which the third (oculomotor) nerve emerges. In the depths of the interpeduncular fossa there is a posterior perforated substance (substantia perforata posterior).

The dorsal part is the quadrigeminal plate, two pairs of colliculi, superior and inferior (culliculi superiores & inferiores). The superior, or visual, colliculi are somewhat larger than the inferior, or auditory, colliculi. The hillocks are connected with structures - the geniculate bodies, the upper ones - with the lateral ones, the lower ones - with the medial ones. From the dorsal side, at the border with the pons, the IV (trochlear) nerve departs, immediately bends around the cerebral peduncles, emerging on the anterior side. There is no clear anatomical border with the diencephalon; the posterior commissure is taken as the rostral border.

Inside the inferior colliculi there are auditory nuclei, and the lateral lemniscus goes there. Around the Sylvian aqueduct is the central gray matter, substantia grisea centralis.

The midbrain is a continuation of the pons. On the basal surface of the brain, the midbrain is separated from the pons quite clearly due to the transverse fibers of the pons. On the dorsal side, the midbrain is delimited from the pons at the level of the transition of the fourth ventricle into the aqueduct and the lower colliculi of the roof. At the level of the transition of the IV ventricle into the midbrain aqueduct, the upper part of the IV ventricle forms the superior medullary velum, where the fibers of the trochlear nerve and the anterior spinocerebellar tract form the intersection.

In the lateral parts of the midbrain, it includes the superior cerebellar peduncles, which, gradually plunging into it, form a decussation at the midline. The dorsal part of the midbrain, located posterior to the aqueduct, is represented by the roof ( tectum mesencephali) with the nuclei of the inferior and superior colliculi.

The structure of the nuclei of the inferior colliculi is simple: they consist of a more or less homogeneous mass of medium-sized nerve cells, playing a significant role in the implementation of complex functions in response to sound stimulation. The nuclei of the superior colliculi are more complexly organized and have a layered structure, participating in the implementation of “automatic” functions associated with visual function, i.e. unconditioned reflexes in response to visual stimulation. In addition, these nuclei coordinate the movements of the torso, facial reactions, movements of the eyes, head, ears, etc. in response to visual stimuli. These reflex reactions are carried out thanks to the tegnospinal and tegmental-bulbar tracts.

Ventral to the superior and inferior colliculi of the roof is the midbrain aqueduct, surrounded by the central one. In the lower part of the tegmentum of the midbrain is the nucleus of the trochlear nerve ( nucl. n. trochlearis), and at the level of the middle and upper sections - a complex of nuclei of the oculomotor nerve ( nucl. n. oculomotorius). The nucleus of the trochlear nerve, consisting of a few large polygonal cells, is localized under the aqueduct at the level of the inferior colliculi. The nuclei of the oculomotor nerve are a complex that includes the main nucleus of the oculomotor nerve, the magnocellular nucleus, similar in morphology to the nuclei of the trochlear and abducens nerves, the small-celled unpaired central posterior nucleus and the outer small-celled accessory nucleus. The nuclei of the oculomotor nerve are located in the tegmentum of the midbrain at the midline, ventral to the aqueduct, at the level of the superior colliculus of the roof of the midbrain.

Important formations of the midbrain are also the red nuclei and the substantia nigra. Red kernels (nucll. ruber) are located ventrolateral to the central gray matter of the midbrain. The red nuclei contain fibers of the anterior cerebellar peduncles, cortical-red nuclear fibers, and fibers from the formations of the striopallidal system. In the red nucleus, the fibers of the red nucleus-spinal cord, as well as the red nucleus-olive tract, begin, fibers going to the cerebral cortex. Thus, the red nucleus is one of the centers involved in the regulation of tone and coordination of movements. When the red nucleus and its pathways are damaged, the animal develops so-called decerebrate rigidity. Ventral to the red nucleus is located black matter (subst. nigra), which seems to separate the tegmentum of the midbrain from its base. The substantia nigra is also involved in the regulation of muscle tone.

The base of the midbrain peduncle consists of fibers that connect the cerebral cortex and other formations of the telencephalon with the underlying formations of the brain stem and. Most of the base is occupied by fibers. In this case, in the medial part there are fibers coming from the frontal areas

The human brain is a complex structure, an organ of the human body that controls all processes in the body. The midbrain is part of its middle section, belongs to the oldest visual center, in the process of evolution it acquired new functions and took a significant place in the life of the human body.

The midbrain is a small (only 2 cm) section of the brain, one of the elements of the brain stem. Located between the subcortex and the posterior part of the brain, it is located in the very center of the organ. It is a connecting segment between the upper and lower structures, since the nerve tracts of the brain pass through it. The anatomical structure is not as complex as the other sections, but in order to understand the structure and functions of the midbrain, it is better to view it in cross section. Then 3 parts of it will be clearly visible.

Roof

In the posterior (dorsal) area there is a quadrigeminal plate, consisting of two pairs of hemispherical colliculi. It is a roof, placed above the water supply, and covered by the cerebral hemispheres. At the top there is a pair of visual hillocks. They are larger in size than the lower elevations. Those hills that lie below are called auditory. The system communicates with the geniculate bodies (elements of the diencephalon), the upper ones with the lateral ones, the lower ones with the medial ones.

Tire

The area follows the roof and includes the ascending tracts of nerve fibers, the reticular formation, the nuclei of the cranial nerves, the medial and lateral (auditory) lemniscus and specific formations.

Brain stems

In the ventral region lie the cerebral peduncles, represented by a pair of ridges. Their main part includes the structure of nerve fibers belonging to the pyramidal system, which diverges to the cerebral hemispheres. The legs cross the longitudinal medial fascicles and include the roots of the oculomotor nerve. In the depths there is a perforated substance. At the base there is white matter, along which descending pathways stretch. In the space between the legs there is a hole where blood vessels pass.

The midbrain is a continuation of the pons, the fibers of which stretch transversely. This makes it possible to clearly see the boundaries of the sections on the basal (main) surface of the brain. From the dorsal site, the restriction occurs from the auditory hills and the transition of the fourth ventricle into the aqueduct.

Midbrain nuclei

In the midbrain, gray matter is located in the form of a concentration of nerve cells, forming the nerve nuclei of the skull:

1. The nuclei of the oculomotor nerve are located in the tegmentum, closer to the middle, ventral to the aqueduct. They form a layered structure and participate in the occurrence of reflexes and visual reactions in response to signals. Also, during the formation of visual stimuli, the nuclei control the movement of the eyes, body, head and facial expressions. The system complex includes the main nucleus, consisting of large cells, and small cell nuclei (central and outer).
2. The nucleus of the trochlear nerve consists of paired elements and is located in the tegmental segment in the region of the inferior colliculi directly under the aqueduct. It is represented by a homogeneous mass of large isodiametric cells. Neurons are responsible for hearing and complex reflexes; with their help, a person reacts to sound stimuli.
3. The reticular formation is represented by a cluster of reticular nuclei and a network of neurons, located in the thickness of the gray matter. In addition to the middle center, it includes the diencephalon and medulla oblongata; the formation is connected with all parts of the central nervous system. It affects motor activity, endocrine processes, affects behavior, attention, memory, inhibition.

Specific education

The structure of the midbrain includes important structural formations. The centers of the extrapyramidal system of the subcortex (a set of structures responsible for movement, body position and muscle activity) include:

Red kernels

In the tegmentum, ventral to the gray matter and dorsal to the substantia nigra, the red nuclei are located. Their color is provided by iron, which appears in the form of ferritin and hemoglobin. Cone-shaped elements stretch from the level of the inferior colliculi to the hypothalamus. They are connected by nerve fibers to the cerebral cortex, cerebellum, and subcortical nuclei. Having received information from these structures about the position of the body, the cone-shaped elements send a signal to the spinal cord and correct muscle tone, preparing the body for the upcoming movement.

If the connection with the reticular formation is disrupted, decerebrate rigidity develops. It is characterized by strong tension in the extensor muscles of the back, neck and limbs.

Black matter

If we consider the anatomy of the midbrain in section, from the pons to the diencephalon in the peduncle two continuous stripes of the black substance are clearly visible. These are clusters of neurons abundantly supplied with blood. The dark color is provided by the pigment melanin. The degree of pigmentation is directly related to the development of structure functions. It appears in a person by 6 months of life, reaching its maximum concentration by 16 years. The substantia nigra divides the stalk into sections:

• dorsal is the tire;
• the ventral section is the base of the leg.

The substance is divided into 2 parts, one of which, the pars compacta, receives signals in the basal ganglia circuit, delivering the hormone dopamine to the telencephalon to the striatum. The second - pars reticulata - transmits signals to other parts of the brain. The nigrostriatal tract originates in the substantia nigra, which is one of the main neural pathways of the brain that initiates motor activity. This section mainly performs conductive functions.

When the substantia nigra is damaged, a person experiences involuntary movements of the limbs and head and difficulty walking. When dopamine neurons die, the activity of this pathway decreases and Parkinson's disease develops. There is an opinion that with an increase in dopamine production, schizophrenia develops.

The cavity of the midbrain is the aqueduct of Salvia, the length of which is approximately one and a half centimeters. A narrow canal runs ventral to the quadrigeminalis and is surrounded by gray matter. This remnant of the primary medullary bladder connects the cavities of the third and fourth ventricles. It contains cerebrospinal fluid.

Functions

All areas of the brain work interconnectedly, together creating a unique system for supporting human life. The main functions of the midbrain are designed to perform the following role:

• Sensory functions. The load for sensory sensations is carried by the neurons of the quadrigeminal nuclei. Signals from the organs of vision and hearing, the cerebral cortex, the thalamus and other brain structures arrive to them along pathways. They provide accommodation of vision to the degree of illumination by changing the size of the pupil; his movement and turns of his head towards the irritating factor.
• Conductor. The midbrain plays the role of a conductor. The base of the legs, nuclei and substantia nigra are mainly responsible for this function. Their nerve fibers are connected to the cortex and underlying brain regions.
• Integrative and motor. Receiving commands from sensory systems, the nuclei convert the signals into active actions. Motor commands are given by the stem generator. They enter the spinal cord, making possible not only muscle contraction, but also the formation of body posture. A person is able to maintain balance in various positions. Reflexive movements are also made when moving the body in space, helping to adapt so as not to lose orientation.

In the midbrain there is a center that regulates the degree of pain. Receiving a signal from the cerebral cortex and nerve fibers, the gray matter begins to produce endogenous opiates, which determine the pain threshold, increasing or decreasing it.

Reflex functions

The midbrain carries out its functions through reflexes. With the help of the medulla oblongata, complex movements of the eyes, head, torso, and fingers are performed. Reflexes are divided into:

• visual;
• auditory;
• sentinel (indicative, answering the question “what is it?”).

They also provide redistribution of skeletal muscle tone. The following types of reactions are distinguished:

• Static ones include two groups - postural reflexes, which are responsible for maintaining a person’s posture, and rectifying ones, which help to return to the normal position if it has been disturbed. This type of reflexes regulates the medulla oblongata and spinal cord, reading data from the vestibular apparatus, with tension in the neck muscles, organs of vision, and skin receptors.
• Statokinetic. Their goal is to maintain balance and orientation in space while moving. A striking example: a cat falling from a height will in any case land on its paws.

The statokinetic group of reflexes is also divided into types.

• With linear acceleration, a lift reflex appears. When a person quickly rises up, the flexor muscles tense; when lowered, the tone of the extensor muscles increases.
• During angular acceleration, for example, during rotation, to maintain visual orientation, nystagmus of the eyes and head occurs: they are turned in the opposite direction.

All reflexes of the midbrain are classified as innate, that is, unconditioned types. An important role in integration processes is assigned to the red core. Its nerve cells activate the skeletal muscles, help maintain the usual body position and take a pose to perform any manipulations.

The substantia nigra is involved in controlling muscle tone and restoring normal posture. The structure is responsible for the sequence of acts of chewing and swallowing; the work of fine motor skills of the hands and eye movements depend on it. The substance is involved in the work of the autonomic system: it regulates the tone of blood vessels, heart rate, and breathing.

Age characteristics and prevention

The brain is a complex structure. It operates with close interaction between all segments. The center that controls the middle section is the cerebral cortex. With age, connections become weaker, and reflex activity weakens. Since the area is responsible for motor function, even minor disruptions in this tiny segment lead to the loss of this important ability. It is more difficult for a person to move, and serious disorders lead to diseases of the nervous system and complete paralysis. How to prevent disorders in the functioning of the brain in order to remain healthy until old age?

First of all, you should avoid hitting your head. If this happens, it is necessary to begin treatment immediately after the injury. It is possible to preserve the functions of the midbrain and the entire organ until old age if you train it with regular exercises:

1. The lifestyle a person leads is important for physical and mental health. Drinking alcohol and smoking destroy neurons, which gradually leads to a decrease in mental and reflex activity. Therefore, you should give up bad habits, and the sooner you do this, the better.
2. Moderate physical activity and walks in nature supply the brain with oxygen, which has a beneficial effect on its activity.
3. You shouldn’t give up reading, solving charades and puzzles: intellectual activity keeps the brain active.
4. An important aspect of the functioning of brain structures is nutrition: fiber, protein, and greens must be present in the diet. The midbrain responds positively to intake of antioxidants and vitamin C.
5. It is necessary to control blood pressure: the health of the vascular system affects the general condition of a person.

The brain is a flexible system that can be successfully developed. Therefore, by constantly improving your mind and body, you can maintain clarity of thoughts and motor activity until old age.

The midbrain, its structure and functions are determined by the location of the structure, providing movement, auditory and visual reactions. If you have difficulty maintaining balance or lethargy, you should consult a doctor and undergo an examination to find the cause of the disturbances and eliminate the problem.

PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM

Spinal cord

Midbrain

Morphofunctional organization. The midbrain (mesencephalon) is represented by the quadrigeminal and cerebral peduncles. The largest nuclei of the midbrain are the red nucleus, the substantia nigra and the nuclei of the cranial (oculomotor and trochlear) nerves, as well as the nuclei of the reticular formation.

Sensory functions. They are realized due to the receipt of visual and auditory information.

Conductor function. It consists in the fact that all ascending pathways to the overlying thalamus (medial lemniscus, spinothalamic tract), cerebrum and cerebellum pass through it. Descending tracts pass through the midbrain to the medulla oblongata and spinal cord. These are the pyramidal tract, corticopontine fibers, and rubroreticulospinal tract.

Motor function. It is realized through the nucleus of the trochlear nerve (n. trochlearis), the nuclei of the oculomotor nerve (n. oculomotorius), the red nucleus (nucleus ruber), and the black substance (substantia nigra).

The red nuclei are located in the upper part of the cerebral peduncles. They are connected to the cerebral cortex (pathways descending from the cortex), subcortical nuclei, cerebellum, and spinal cord (red nuclear-spinal tract). The basal ganglia of the brain and the cerebellum have their endings in the red nuclei. Disruption of connections between the red nuclei and the reticular formation of the medulla oblongata leads to decerebrate rigidity. This condition is characterized by severe tension in the extensor muscles of the limbs, neck, and back. The main cause of decerebrate rigidity is the pronounced activating influence of the lateral vestibular nucleus (Deiters nucleus) on extensor motor neurons. This influence is maximum in the absence of inhibitory influences of the red nucleus and overlying structures, as well as the cerebellum. When the brain is transected below the nucleus of the lateral vestibular nerve, decerebrate rigidity disappears.

The red nuclei, receiving information from the motor zone of the cerebral cortex, subcortical nuclei and cerebellum about the impending movement and the state of the musculoskeletal system, send corrective impulses to the motor neurons of the spinal cord along the rubrospinal tract and thereby regulate muscle tone, preparing its level for the upcoming voluntary movement .

Another functionally important nucleus of the midbrain - the substantia nigra - is located in the cerebral peduncles, regulates the acts of chewing, swallowing (their sequence), and ensures precise movements of the fingers of the hand, for example when writing. The neurons of this nucleus are capable of synthesizing the neurotransmitter dopamine, which is supplied by axonal transport to the basal ganglia of the brain. Damage to the substantia nigra leads to disruption of plastic muscle tone. Fine regulation of plastic tone when playing the violin, writing, and doing graphic work is ensured by the substantia nigra. At the same time, when holding a certain position for a long time, plastic changes occur in the muscles due to changes in their colloidal properties, which ensures the least energy expenditure. Regulation of this process is carried out by the cells of the substantia nigra.

Neurons of the oculomotor and trochlear nerve nuclei regulate the movement of the eye up, down, out, toward the nose, and down toward the corner of the nose. Neurons of the accessory nucleus of the oculomotor nerve (Yakubovich's nucleus) regulate the lumen of the pupil and the curvature of the lens.

Reflex functions. Functionally independent structures of the midbrain are the quadrigeminal tuberosities. The upper ones are the primary subcortical centers of the visual analyzer (together with the lateral geniculate bodies of the diencephalon), the lower ones are the auditory centers (together with the medial geniculate bodies of the diencephalon). They are where the primary switching of visual and auditory information occurs. From the quadrigeminal tuberosities, the axons of their neurons go to the reticular formation of the trunk, the motor neurons of the spinal cord. Quadrigeminal neurons can be multimodal and detector. In the latter case, they react only to one sign of irritation, for example, a change in light and darkness, the direction of movement of the light source, etc. The main function of the quadrigeminal tuberosities is the organization of an alert reaction and the so-called start reflexes to sudden, not yet recognized, visual or sound signals. Activation of the midbrain in these cases through the hypothalamus leads to increased muscle tone and increased heart contractions; preparation for avoidance and a defensive reaction occurs.

The quadrigeminal region organizes indicative visual and auditory reflexes.

In humans, the quadrigeminal reflex is a sentinel reflex. In cases of increased excitability of the quadrigeminals, with sudden sound or light stimulation, a person begins to flinch, sometimes jump to his feet, scream, move away from the stimulus as quickly as possible, and sometimes run away uncontrollably.

If the quadrigeminal reflex is impaired, a person cannot quickly switch from one type of movement to another. Consequently, the quadrigeminal muscles take part in the organization of voluntary movements.

Reticular formation of the brainstem

The reticular formation (formatio reticularis; RF) of the brain is represented by a network of neurons with numerous diffuse connections among themselves and with almost all structures of the central nervous system. The RF is located in the thickness of the gray matter of the medulla oblongata, midbrain, and diencephalon and is initially associated with the RF of the spinal cord. In this regard, it is advisable to consider it as a single system. The network connections of RF neurons among themselves allowed Deiters to call it the reticular formation of the brain.

The RF has direct and inverse connections with the cerebral cortex, basal ganglia, diencephalon, cerebellum, midbrain, medulla oblongata and spinal cord.

The main function of the Russian Federation is to regulate the level of activity of the cerebral cortex, cerebellum, thalamus, and spinal cord.

On the one hand, the generalized nature of the influence of the Russian Federation on many brain structures gives grounds to consider it a nonspecific system. However, studies with irritation of the RF trunk have shown that it can selectively have an activating or inhibitory effect on various forms of behavior, on the sensory, motor, and visceral systems of the brain. The network structure ensures high reliability of the functioning of the Russian Federation and resistance to damaging influences, since local damage is always compensated by the surviving network elements. On the other hand, the high reliability of the functioning of the Russian Federation is ensured by the fact that irritation of any of its parts is reflected in the activity of the entire Russian Federation of a given structure due to the diffuseness of connections.

Most RF neurons have long dendrites and short axons. There are giant neurons with long axons that form pathways from the RF to other brain regions, such as descending, reticulospinal, and rubrospinal. The axons of RF neurons form a large number of collaterals and synapses that end on neurons of various parts of the brain. The axons of RF neurons going to the cerebral cortex end here on the dendrites of layers I and II.

The activity of RF neurons is different and, in principle, similar to the activity of neurons in other brain structures, but among the RF neurons there are those that have stable rhythmic activity that does not depend on incoming signals.

At the same time, in the RF of the midbrain and pons there are neurons that are “silent” at rest, that is, they do not generate impulses, but are excited when visual or auditory receptors are stimulated. These are so-called specific neurons that provide a quick response to sudden, unidentified signals. A significant number of RF neurons are multisensory.

In the RF of the medulla oblongata, midbrain and pons, signals of different sensory properties converge. The neurons of the bridge receive signals mainly from somatosensory systems. Signals from the visual and auditory sensory systems mainly arrive at the midbrain RF neurons.

The RF controls the transmission of sensory information passing through the nuclei of the thalamus due to the fact that, with intense external stimulation, the neurons of the nonspecific nuclei of the thalamus are inhibited, thereby removing their inhibitory influence from the relay nuclei of the same thalamus and facilitating the transfer of sensory information to the cerebral cortex.

In the RF of the pons, medulla oblongata, and midbrain there are neurons that respond to painful stimuli coming from muscles or internal organs, which creates a general diffuse uncomfortable, not always clearly localized, painful sensation of “dull pain.”

Repeating any type of stimulation leads to a decrease in the impulse activity of RF neurons, i.e., adaptation processes (habituation) are also inherent in RF neurons of the brain stem.

The RF of the brain stem is directly related to the regulation of muscle tone, since the RF of the brain stem receives signals from the visual and vestibular analyzers and the cerebellum. From the RF, signals are sent to the motor neurons of the spinal cord and cranial nerve nuclei that organize the position of the head, torso, etc.

Reticular tracts that facilitate the activity of the motor systems of the spinal cord originate from all parts of the Russian Federation. Pathways from the pons inhibit the activity of spinal cord motor neurons that innervate flexor muscles and activate spinal motor neurons that innervate extensor muscles. The pathways coming from the RF of the medulla oblongata cause opposite effects. Irritation of the Russian Federation leads to tremor and increased muscle tone. After the cessation of stimulation, the effect caused by it persists for a long time, apparently due to the circulation of excitation in the network of neurons.

The brainstem RF is involved in the transmission of information from the cerebral cortex, spinal cord to the cerebellum and, conversely, from the cerebellum to the same systems. The function of these connections is to prepare and implement motor skills associated with habituation, indicative reactions, pain reactions, organization of walking, and eye movements.

The regulation of the vegetative activity of the body of the Russian Federation is described in section 4.3, but we note here that this regulation is most clearly manifested in the functioning of the respiratory and cardiovascular centers. The so-called RF starter neurons are of great importance in the regulation of autonomic functions. They give rise to the circulation of excitation within a group of neurons, providing the tone of regulated autonomic systems.

The influences of the Russian Federation can be generally divided into downward and upward. In turn, each of these influences has an inhibitory and excitatory effect.

The ascending influences of the RF on the cerebral cortex increase its tone and regulate the excitability of its neurons without changing the specificity of responses to adequate stimulation. RF affects the functional state of all sensory areas of the brain, therefore, it is important in the integration of sensory information from different analyzers.

RF is directly related to the regulation of the sleep-wake cycle. Stimulation of some structures of the Russian Federation leads to the development of sleep, stimulation of others causes awakening. G. Magun and D. Moruzzi put forward the concept according to which all types of signals coming from peripheral receptors reach the RF collaterals of the medulla oblongata and the pons, where they switch to neurons that give ascending pathways to the thalamus and then to the cerebral cortex.

Excitation of the RF of the medulla oblongata or pons causes synchronization of the activity of the cerebral cortex, the appearance of slow rhythms in its electrical parameters, and sleep inhibition.

Excitation of the midbrain RF causes the opposite effect of awakening: desynchronization of the electrical activity of the cortex, the appearance of fast low-amplitude β-like rhythms in the electroencephalogram.

G. Bremer (1935) showed that if the brain is cut between the anterior and posterior colliculi, the animal stops responding to all types of signals; if a transection is made between the medulla oblongata and the midbrain (while the RF retains its connection with the forebrain), then the animal reacts to light, sound and other signals. Consequently, maintaining an active analyzing state of the brain is possible while maintaining connections with the forebrain.

The activation reaction of the cerebral cortex is observed upon stimulation of the RF of the medulla oblongata, midbrain, and diencephalon. At the same time, irritation of some nuclei of the thalamus leads to the emergence of limited local areas of excitation, and not to its general excitation, as happens with irritation of other parts of the Russian Federation.

RF of the brain stem can have not only an excitatory, but also an inhibitory effect on the activity of the cerebral cortex.

The descending influences of the brainstem RF on the regulatory activity of the spinal cord were established by I.M. Sechenov (1862). They showed that when the midbrain is irritated by salt crystals, the frog's paw withdrawal reflexes arise slowly, require stronger stimulation, or do not appear at all, i.e., they are inhibited.

G. Magun (1945-1950), applying local irritations to the RF of the medulla oblongata, found that when certain points are irritated, the flexion reflexes of the forepaw, knee, and cornea are inhibited and become sluggish. When the RF was stimulated at other points of the medulla oblongata, these same reflexes were evoked more easily and were stronger, i.e. their implementation was facilitated. According to Magun, only the RF of the medulla oblongata can exert inhibitory influences on the reflexes of the spinal cord, while facilitating influences are regulated by the entire RF of the brainstem and spinal cord.

Main manifestations of bridge lesions

If the bridge is partially damaged (for example, with strokes, traumatic brain injuries, some infections, etc.), a person experiences neurological symptoms in the form central paralysis (paresis). Additionally, lesions of the pontine nuclei are detected. In particular, symptoms of so-called oral automatism appear - involuntary movements carried out through the orbicularis oris, lips or masticatory muscles in response to mechanical or other irritation of certain areas of the skin, which is due to the involvement of the V and VII pairs of cranial nerves in the process. Development of symptoms of oral automaticity

due to the functional separation of the cortex and subcortical structures.

Oculomotor disorders with damage to the bridge are manifested by convergent strabismus. This is due to dysfunction of the abducens nerve, the motor nucleus of which is localized in the pons. The eyeball on the affected side cannot be abducted outward (in mild disorders, weakness in its abduction occurs).

When the bridge is damaged, the syndrome may sometimes appear "locked man", or Villefort syndrome(but named after a literary character from A. Dumas’ novel “The Count of Monte Cristo”), it is characterized by the absence of all voluntary movements, the presence of pseudobulbar palsy, aphonia, dysphagia, immobility of the tongue and the absence of facial movements, except for movements of the eyeballs and blinking - the so-called painting of a "corpse with living eyes". At the same time, the person is conscious - he sees, hears and understands everything.

Midbrain

External building. The midbrain develops from the midbrain. In functional terms, it is the subcortical motor center of the extrapyramidal system - it is responsible for the unconditioned reflex regulation of muscle tone and unconditioned reflex movements caused by super-strong and unusual visual, sound, tactile and olfactory stimuli. The midbrain was formed as an integration subcortical center of these functions.

Compared to other sections, the midbrain is small in size. Its ventral surface is represented by the cerebral peduncles. The dorsal surface is formed by the plate of the roof (plate of the quadrigeminal) of the midbrain. The cavity is the aqueduct of the midbrain (Aqueduct of Sylvius).

On the ventral side, the cerebral peduncles look like two thick flattened ridges that appear from under the upper edge of the pons (see Fig. 3.3). From here they are directed upward and to the sides at an angle of 70–80° and are immersed in the substance of the diencephalon. The anterior border of the cerebral peduncles is the optic tract, which is referred to as the diencephalon.

On the ventral side between the two cerebral peduncles there is a triangular-shaped depression called the interpeduncular fossa. It is narrower, at the upper edge of the bridge it expands anteriorly and ends near the two mastoid bodies belonging to the diencephalon. The surface of the interpeduncular fossa has a grayish color and is dotted with holes through which numerous blood vessels pass. This area of ​​the brain is called the posterior perforated substance.

Along the medial edge of the cerebral peduncles there is a groove of the oculomotor nerve, from which the oculomotor nerve, the third pair of cranial nerves, emerges as one root.

On the dorsal surface of the midbrain, represented by the roof plate, there are four rounded elevations - two superior and two inferior colliculi (see Fig. 3.4, 3.5). The mounds are separated by grooves intersecting at right angles. The lower hillocks are smaller than the upper ones.

The handles of the hillocks extend from each hillock on the lateral side. They move forward and upward to the diencephalon. The handles of the superior colliculi, narrower and longer, end in the lateral geniculate bodies, the handles of the lower colliculi, thicker and shorter, end in the medial geniculate bodies.

Posterior to the inferior colliculi along the midline is the frenulum of the superior medullary velum, which has a triangular shape. On each side of the frenulum of the superior medullary velum, one root of the fourth pair of cranial nerves emerges. The trochlear nerve, the fourth pair of cranial nerves, is the thinnest of all cranial nerves and the only one that emerges from the substance of the brain on its dorsal surface. The nerve then bends around the cerebral peduncles and goes to their ventral surface.

On the lateral surface of the midbrain, in the interval between the lateral sulcus of the midbrain and the handles of the inferior colliculi, a triangular-shaped area is distinguished - a triangle of loops. The third side of the triangle is the lateral edge of the superior cerebellar peduncle. In the projection of the triangle, in the thickness of the cerebral peduncles, nerve fibers pass that make up the lateral, medial, trigeminal and spinal lemniscus. Thus, in this place, in a small area near the surface of the brain, almost all the pathways of general sensitivity (conducting impulses to the diencephalon) and the auditory pathway are concentrated.

The cavity of the midbrain is the midbrain aqueduct (aqueduct of the brain). It is a remnant of the cavity of the middle cerebral bladder, oriented along the axis of the brain, connecting the third and fourth ventricles. Its length is about 15 mm, average diameter is 1–2 mm. There is a slight expansion in the middle part of the cerebral aqueduct.

Internal structure. A cross-section of the midbrain clearly identifies its main parts: above the aqueduct there is a plate of the roof, below there are the cerebral peduncles (Fig. 3.10). A section through the cerebral peduncles reveals a pigmented layer of gray matter called the substantia nigra (Semmering's substance). The substantia nigra delimits the base of the cerebral peduncle and the tegmentum of the midbrain.

On a cross section, the substantia nigra has the shape of a flattened crescent with a convexity facing ventrally. The dorsal part of the substantia nigra contains highly pigmented nerve cells containing large amounts of iron. The ventral part of the substantia nigra contains large scattered nerve cells and myelin fibers passing between them.

Rice. 3.10.

1 – medial longitudinal fasciculus; 2 – cerebral aqueduct; 3 – nucleus of the superior colliculus; 4 – roof-spinal tract; 5 – red core; 6 – black substance; 7 – occipital-temporal-pontine tract; 8 – corticospinal tract; 9 – cortical-nuclear pathway; 10 – frontopontine tract; 11 – red nucleus-spinal tract; 12 – bulbarnotalamic tract; 13 – spinothalamic tract; 14 – nuclear-thalamic pathway; 15 – auditory pathway

The base of the cerebral peduncle is formed mainly by longitudinally oriented descending fibers that go from the neurons of the cerebral cortex to the nuclei of the brain stem and spinal cord. In this regard, the base of the cerebral peduncles is a phylogenetically new formation.

The tegmentum of the midbrain contains gray and white matter. The gray matter is represented by the paired red nucleus and the central gray matter located around the cerebral aqueduct.

The red nuclei are cylindrical in shape, located throughout the entire midbrain in the center of the tegmentum of each cerebral peduncle and partially continue into the diencephalon.

The cells of the red nucleus, like the cells of the substantia nigra, contain iron, but in much smaller quantities. The neurons of the red nucleus terminate in the fibers of the dentate-red nuclear tract and the axons of the cells of the basal nuclei of the telencephalon, forming the striatal-red nuclear tract. The axons of large cells of the red nucleus unite into the red nucleus-spinal cord and red nucleus-nuclear tract. The axons of small neurons of the red nucleus end on the neurons of the reticular formation and olives of the medulla oblongata, forming the red nuclear-reticular and red nuclear-olive tracts.

Surrounding the brain's aqueduct is the central gray matter. In the ventrolateral part of this substance, at the level of the inferior colliculi, the motor nuclei of the fourth pair of cranial nerves - the trochlear nerve - are located. The axons of the neurons of these nuclei are directed dorsally, pass to the opposite side and exit the brain substance in the region of the frenulum of the superior medullary velum. Cranial to the motor nuclei of the IV pair of cranial nerves (at the level of the superior colliculi) are the nuclei of the III pair of cranial nerves - the oculomotor nerve.

The oculomotor nerve has three nuclei. The motor nucleus is the largest and has an elongated shape. It has five segments, each of which provides innervation to certain muscles of the eyeball and the muscle that lifts the upper eyelid.

In addition to this nucleus, the oculomotor nerve also has a central unpaired nucleus. This nucleus is associated with the caudal segments of the motor nuclei of both sides, which are responsible for the innervation of the medial rectus muscles. This ensures the combined work of the indicated muscles of the right and left eyeballs, which rotate the eyeball and bring the pupils closer to the median plane. Due to its function, the central unpaired nucleus is also called convergent.

Dorsal from the motor nuclei, near the midline, there are autonomic nuclei - the so-called accessory nuclei of the oculomotor nerve (Yakubovich's nuclei). The neurons of these nuclei are responsible for the innervation of the constrictor pupillary muscle and the ciliary muscle. The names of the nuclei of the cranial nerves of the midbrain and their functional purpose are given in Table. 3.4.

Table 3.4

Cranial nerves of the midbrain and their nuclei

Some fibers from the motor nuclei of the oculomotor nerve participate in the formation of the medial longitudinal fasciculus. Most of the fibers from all nuclei make up the root of the oculomotor nerve, which exits the brain substance in the groove of the same name.

In the lateral part of the central gray matter is the nucleus of the midbrain tract of the trigeminal nerve (midcerebral nucleus).

Between the central gray matter and the red nuclei is the reticular formation, which contains numerous small nuclei and two large nuclei. One of them is called the intermediate nucleus (Cajal nucleus), the second is the nucleus of the posterior commissure (Darkshevich nucleus). The axons of the cells of the Cajal nucleus and the Darkshevich nucleus are sent to the spinal cord, forming the medial longitudinal fasciculus.

The medial longitudinal fasciculus contains nerve fibers that provide connection between the nuclei of the reticular formation and the motor nuclei of the III, IV, VI and XI pairs of cranial nerves. Consequently, the Cajal nucleus and the Darkshevich nucleus are centers for coordinating the combined function of the muscles of the eyeball and the muscles of the neck. Since the function of these muscles is most pronounced during vestibular loads, the nuclei of the reticular formation receive afferent impulses from the vestibular nuclei of the pons (nuclei of the VIII pair of cranial nerves).

Next to the medial longitudinal fasciculus is the posterior longitudinal fasciculus, which starts from the structures of the diencephalon. The fibers of this bundle are directed to the autonomic nuclei of the cranial nerves and spinal cord. They ensure coordination of the activity of the autonomic centers of the brain stem and spinal cord.

Dorsal to the cerebral aqueduct is the roof of the midbrain. It consists of two pairs of mounds - upper and lower, which differ significantly in structure. In humans, the superior colliculi are more developed, since the majority of information is received through the organ of vision. The superior colliculus represents the integration center of the midbrain and, in addition, is one of the subcortical centers of vision, smell and tactile sensitivity. Some of the fibers of the lateral lemniscus end on the neurons of the inferior colliculus nuclei. They are subcortical hearing centers. Part of the fibers of the lateral lemniscus, as part of the handles of the inferior colliculi, is directed to the nucleus of the medial geniculate body of the diencephalon.

The superior colliculi have a pronounced layered arrangement of neurons, which is characteristic of integration centers (cerebellar cortex and cerebral cortex). The fibers of the optic tracts end in the superficial layers of the superior colliculi. In the deep layers, sequential synaptic switching of fibers and integration of visual, auditory, olfactory, gustatory and tactile sensitivity occurs.

The axons of neurons in the deep layers form a bundle, which is located lateral to the central gray matter. The bundle contains two tracts: the roof-spinal tract and the roof-nuclear bundle. The fibers of these tracts pass to the opposite side, forming the posterior decussation of the tegmentum (decussation of Meynert), which is located ventral to the aqueduct of Sylvius.

The fibers of the roof-spinal tract end on the neurons of the own nuclei of the anterior horns of the spinal cord. The fibers of the roof nuclear bundle end on the neurons of the motor nuclei of the cranial nerves. The roof-spinal and roof-nuclear tracts conduct nerve impulses that ensure the performance of protective reflex movements (alertness, flinching, jumping to the side) in response to various strong irritations (visual, auditory, olfactory and tactile).

The base of the cerebral peduncles is formed only in the higher cranial ones, therefore, it contains phylogenetically new pathways. They are represented by bundles of longitudinal efferent fibers that originate from the telencephalon. These fibers originate from the cells of the cerebral cortex and are directed to the cerebellum, pons, medulla oblongata and spinal cord. The pathway running from the cerebral cortex to the cerebellum is interrupted in the pons own nuclei and consists of two parts - the corticopontine and pontocerebellar tracts.

Part of the fibers of the cortical-pontine tract, originating from the neurons of the frontal lobe cortex, occupies the medial part of the base of the cerebral peduncles. These fibers make up the frontopontine tract. Fibers starting from the neurons of the cortex of the occipital and temporal lobes pass in the lateral part of the base of the cerebral peduncles and unite under the name of the occipital-temporal-pontine tract.

Pyramidal fibers, derived from the pyramidal cells of the cerebral cortex, are located in the middle of the base of the cerebral peduncles. Of these, the medial part is occupied by the cortical-nuclear tract. This pathway ends at the neurons of the motor nuclei of the cranial nerves of the brain stem. Lateral to the corticonuclear tract is the corticospinal tract. Its fibers end on the neurons of the own nuclei of the anterior horns of the spinal cord.

In the tegmentum of the cerebral peduncles, lateral to the red nuclei, there are the following bundles of afferent fibers: medial, spinal, trigeminal and lateral lemniscus.

Also in the tegmentum of the cerebral peduncles, ventral to the central gray matter, is the medial longitudinal fasciculus. It is formed by axons of neurons of the interstitial nucleus and axons of neurons of the nucleus of the posterior commissure.

Ventral to the medial longitudinal fasciculus is the roof-spinal tract, formed by the axons of the cells of the superior colliculus. Already in the midbrain, this pathway passes to the opposite side, forming the previously described posterior tegmental decussation (Meynert's decussation).

From the neurons of the red nuclei, the red nuclear-spinal tract begins, which is called the Monakov bundle. Ventral to the red nuclei, this path also passes to the opposite side, forming the anterior decussation of the tegmentum (Trout decussation).

Main manifestations of midbrain lesions

Damage to the midbrain (cerebral circulation disorders, brainstem tumors, traumatic brain injuries, neuroinfections, etc.) can lead to impaired vision, hearing, disorders of eyeball movement, pupillary reaction to light, sleep disturbances, motor activity, cerebellar disorders and etc., the severity of which depends on the location and degree of damage.

The development of divergent strabismus with damage to the midbrain is associated with dysfunction of the nuclei of the oculomotor nerve. Movement of the eyeball inwards, up and down becomes weakened or becomes impossible.

In severe illnesses and injuries, Magendie's symptom develops. It is characterized by the difference in the distance of the pupils along the vertical axis.

With midbrain roof lesion syndrome ( quadrigeminal syndrome) increased orienting reflexes to light and auditory stimuli are observed - a rapid turn of the head and eyeballs towards the stimulus, with the simultaneous addition of divergent strabismus, “floating” movements of the eyeballs and “doll” (wide open) eyes. These manifestations are often accompanied by bilateral hearing loss.

Some authors associate the development of attention disorder (or deficit) with hyperactivity disorder (ADHD or ADHD) with damage to midbrain structures. This is one of the common childhood behavioral disorders, which in some individuals persists into adulthood. The neurophysiological mechanism for the development of ADHD may be associated with the activation of midbrain structures and the reticular formation of the brain stem. ADHD manifests itself as a triad: impaired attention, hyperactivity, and a tendency to impulsive behavior.

Lesions in the midbrain area can be the cause of auditory and especially visual hallucinations described by the French neurologist J. Lhermitte. This syndrome is observed in patients with neoplasms, inflammatory and vascular disorders in the quadrigeminal region, manifesting itself as visual colorful deceptions of perception of zoological content (visions of fish, birds, small animals, people, etc.). In this case, tactile illusions of perception are also often observed. Hallucinatory visual images are mobile, bizarre, complex, often have a scene-like character, and are characterized by the predominant appearance of visual hallucinations at dusk or when falling asleep. It is important to note that patients maintain a critical attitude towards hallucinations, consciousness is not impaired, and psychomotor agitation is not noted.

Midbrain comprises:

Bugrov quadrigeminal,

red core,

substantia nigra,

Seam cores.

Red core– provides the tone of skeletal muscles, redistribution of tone when changing posture. Just stretching is a powerful activity of the brain and spinal cord, for which the red nucleus is responsible. The red core ensures the normal tone of our muscles. If the red nucleus is destroyed, decerebrate rigidity occurs, with a sharp increase in the tone of the flexors in some animals and the extensors in others. And with absolute destruction, both tones increase at once, and it all depends on which muscles are stronger.

Black substance– How is excitation from one neuron transmitted to another neuron? Excitation occurs - this is a bioelectric process. It reaches the end of the axon, where a chemical substance is released - a transmitter. Each cell has its own mediator. A transmitter is produced in the substantia nigra in nerve cells dopamine. When the substantia nigra is destroyed, Parkinson's disease occurs (the fingers and head constantly tremble, or there is stiffness as a result of a constant signal being sent to the muscles) because there is not enough dopamine in the brain. The substantia nigra provides subtle instrumental movements of the fingers and influences all motor functions. The substantia nigra exerts an inhibitory effect on the motor cortex through the stripolidal system. If it is disrupted, it is impossible to perform delicate operations and Parkinson's disease occurs (stiffness, tremors).

Above are the anterior tubercles of the quadrigeminal, and below are the posterior tubercles of the quadrigeminal. We look with our eyes, but we see with the occipital cortex of the cerebral hemispheres, where the visual field is located, where the image is formed. A nerve leaves the eye, passes through a number of subcortical formations, reaches the visual cortex, there is no visual cortex, and we will not see anything. Anterior tubercles of the quadrigeminal- This is the primary visual area. With their participation, an indicative reaction to a visual signal occurs. The indicative reaction is the “reaction what is it?” If the anterior tubercles of the quadrigeminal are destroyed, vision will be preserved, but there will be no quick reaction to the visual signal.

Posterior tubercles of the quadrigeminal This is the primary auditory zone. With its participation, an indicative reaction to the sound signal occurs. If the posterior tubercles of the quadrigeminal are destroyed, hearing will be preserved but there will be no indicative reaction.

Seam cores– this is the source of another mediator serotonin. This structure and this mediator takes part in the process of falling asleep. If the suture nuclei are destroyed, the animal is in a constant state of wakefulness and quickly dies. In addition, serotonin takes part in positive reinforcement learning (this is when a rat is given cheese). Serotonin provides character traits such as unforgivingness, goodwill; aggressive people have a lack of serotonin in the brain.

12) The thalamus is a collector of afferent impulses. Specific and nonspecific nuclei of the thalamus. The thalamus is the center of pain sensitivity.

Thalamus- visual thalamus. He was the first to discover his relationship to visual impulses. It is a collector of afferent impulses, those that come from receptors. The thalamus receives signals from all receptors except the olfactory ones. The thalamus receives information from the cortex, the cerebellum, and the basal ganglia. At the level of the thalamus, these signals are processed, only the most important information for a person at a given moment is selected, which then enters the cortex. The thalamus consists of several dozen nuclei. The nuclei of the thalamus are divided into two groups: specific and nonspecific. Through specific nuclei of the thalamus, signals arrive strictly to certain areas of the cortex, for example, visual to the occipital lobe, auditory to the temporal lobe. And through nonspecific nuclei, information diffuses to the entire cortex in order to increase its excitability in order to more clearly perceive specific information. They prepare the BP cortex for the perception of specific information. The highest center of pain sensitivity is the thalamus. The thalamus is the highest center of pain sensitivity. Pain is formed necessarily with the participation of the thalamus, and when some nuclei of the thalamus are destroyed, pain sensitivity is completely lost; when other nuclei are destroyed, barely bearable pain occurs (for example, phantom pain is formed - pain in a missing limb).

13) Hypothalamic-pituitary system. The hypothalamus is the center of regulation of the endocrine system and motivation.

The hypothalamus and pituitary gland form a single hypothalamic-pituitary system.

Hypothalamus. The pituitary stalk departs from the hypothalamus, on which it hangs pituitary- main endocrine gland. The pituitary gland regulates the functioning of other endocrine glands. The hypoplamus is connected to the pituitary gland by nerve pathways and blood vessels. The hypothalamus regulates the work of the pituitary gland, and through it the work of other endocrine glands. The pituitary gland is divided into adenohypophysis(glandular) and neurohypophysis. In the hypothalamus (this is not an endocrine gland, it is a part of the brain) there are neurosecretory cells in which hormones are secreted. This is a nerve cell; it can be excited, it can be inhibited, and at the same time hormones are secreted in it. An axon extends from it. And if these are hormones, they are released into the blood, and then go to the decision organs, i.e. to the organ whose work it regulates. Two hormones:

- vasopressin – promotes the conservation of water in the body, it affects the kidneys, and with its deficiency, dehydration occurs;

- oxytocin – produced here, but in other cells, ensures contraction of the uterus during childbirth.

Hormones are secreted in the hypothalamus and released by the pituitary gland. Thus, the hypothalamus is connected to the pituitary gland via nerve pathways. On the other hand: nothing is produced in the neurohypophysis; hormones come here, but the adenohypophysis has its own glandular cells, where a number of important hormones are produced:

- ganadotropic hormone – regulates the functioning of the sex glands;

- thyroid-stimulating hormone – regulates the functioning of the thyroid gland;

- adrenocorticotropic – regulates the functioning of the adrenal cortex;

- somatotropic hormone, or growth hormone, – ensures the growth of bone tissue and the development of muscle tissue;

- melanotropic hormone – is responsible for pigmentation in fish and amphibians, in humans it affects the retina.

All hormones are synthesized from a precursor called proopiomellanocortin. A large molecule is synthesized, which is broken down by enzymes, and other hormones, smaller in number of amino acids, are released from it. Neuroendocrinology.

The hypothalamus contains neurosecretory cells. They produce hormones:

1) ADH (antidiuretic hormone regulates the amount of urine excreted)

2) oxytocin (provides contraction of the uterus during childbirth).

3) statins

4) liberins

5) thyroid-stimulating hormone affects the production of thyroid hormones (thyroxine, triiodothyronine)

Thyroliberin -> thyroid-stimulating hormone -> thyroxine -> triiodothyronine.

The blood vessel enters the hypothalamus, where it branches into capillaries, then the capillaries gather and this vessel passes through the pituitary stalk, branches again in the glandular cells, leaves the pituitary gland and carries with it all these hormones, which each go with the blood to its own gland. Why is this “wonderful vascular network” needed? There are nerve cells in the hypothalamus that end on the blood vessels of this wonderful vascular network. These cells produce statins And liberins - This neurohormones. Statins inhibit the production of hormones in the pituitary gland, and liberins it is strengthened. If there is an excess of growth hormone, gigantism occurs, this can be stopped with the help of samatostatin. On the contrary: the dwarf is injected with samatoliberin. And apparently there are neurohormones for any hormone, but they are not yet discovered. For example, the thyroid gland produces thyroxine, and in order to regulate its production, the pituitary gland produces thyroid-stimulating hormone, but in order to control thyroid-stimulating hormone, thyreostatin has not been found, but thyroliberin is used perfectly. Although these are hormones, they are produced in nerve cells, so in addition to their endocrine effects, they have a wide range of extraendocrine functions. Thyroid hormone is called panactivin, because it improves mood, improves performance, normalizes blood pressure, and accelerates healing in case of spinal cord injuries; it is the only thing that cannot be used for disorders of the thyroid gland.

The functions associated with neurosecretory cells and cells that produce neurofebtides were previously discussed.

The hypothalamus produces statins and liberins, which are included in the body's stress response. If the body is affected by some harmful factor, then the body must somehow respond - this is the stress reaction of the body. It cannot occur without the participation of statins and liberins, which are produced in the hypothalamus. The hypothalamus necessarily takes part in the response to stress.

The following functions of the hypothalamus are:

It contains nerve cells that are sensitive to steroid hormones, i.e. sex hormones, both female and male sex hormones. This sensitivity ensures formation of a female or male type. The hypothalamus creates the conditions for motivating behavior according to the male or female type.

A very important function is thermoregulation; the hypothalamus contains cells that are sensitive to blood temperature. Body temperature can change depending on the environment. Blood flows through all structures of the brain, but thermoreceptive cells, which detect the slightest changes in temperature, are found only in the hypothalamus. The hypothalamus turns on and organizes two responses of the body: heat production or heat transfer.

Food motivation. Why does a person feel hungry?

The signaling system is the level of glucose in the blood, it should be constant ~120 milligrams% - s.

There is a mechanism of self-regulation: if our blood glucose level decreases, liver glycogen begins to break down. On the other hand, glycogen reserves are not enough. The hypothalamus contains glucoreceptive cells, i.e. cells that record the level of glucose in the blood. Glucoreceptive cells form hunger centers in the hypothalamus. When blood glucose levels drop, these blood glucose-sensing cells become excited and a feeling of hunger occurs. At the level of the hypothalamus, only food motivation arises - a feeling of hunger; to search for food, the cerebral cortex must be involved, with its participation a true food reaction arises.

The satiety center is also located in the hypothalamus, it inhibits the feeling of hunger, which protects us from overeating. When the saturation center is destroyed, overeating occurs and, as a result, bulimia.

The hypothalamus also contains the thirst center - osmoreceptive cells (osmatic pressure depends on the concentration of salts in the blood). Osmoreceptive cells record the level of salts in the blood. When salts in the blood increase, osmoreceptive cells are excited, and drinking motivation (reaction) occurs.

The hypothalamus is the highest control center of the autonomic nervous system.

The anterior sections of the hypothalamus mainly regulate the parasympathetic nervous system, the posterior sections mainly regulate the sympathetic nervous system.

The hypothalamus provides only motivation and goal-directed behavior to the cerebral cortex.

14) Neuron – structural features and functions. Differences between neurons and other cells. Glia, blood-brain barrier, cerebrospinal fluid.

I Firstly, as we have already noted, in their diversity. Any nerve cell consists of a body - soma and processes. Neurons are different:

1. by size (from 20 nm to 100 nm) and shape of the soma

2. by the number and degree of branching of short processes.

3. according to the structure, length and branching of axon endings (laterals)

4. by the number of spines

II Neurons also differ in functions:

A) perceivers information from the external environment,

b) transmitting information to the periphery,

V) processing and transmitting information within the central nervous system,

G) exciting,

d) brake.

III Differ in chemical composition: various proteins, lipids, enzymes are synthesized and, most importantly, - mediators .

WHY, WHAT FEATURES IS THIS ASSOCIATED WITH?

Such diversity is determined high activity of the genetic apparatus neurons. During neuronal induction, under the influence of neuronal growth factor, NEW GENES are turned on in the cells of the ectoderm of the embryo, which are characteristic only of neurons. These genes provide the following features of neurons ( the most important properties):

A) The ability to perceive, process, store and reproduce information

B) DEEP SPECIALIZATION:

0. Synthesis of specific RNA;

1. No reduplication DNA.

2. The proportion of genes capable of transcriptions, make up in neurons 18-20%, and in some cells – up to 40% (in other cells - 2-6%)

3. The ability to synthesize specific proteins (up to 100 in one cell)

4. Unique lipid composition

B) Privilege of nutrition => Dependence on level oxygen and glucose in blood.

Not a single tissue in the body is in such a dramatic dependence on the level of oxygen in the blood: 5-6 minutes of stopping breathing and the most important structures of the brain die, and first of all the cerebral cortex. A decrease in glucose levels below 0.11% or 80 mg% - hypoglycemia may occur and then coma.

On the other hand, the brain is fenced off from the blood flow by the BBB. It does not allow anything into the cells that could harm them. But, unfortunately, not all of them - many low-molecular toxic substances pass through the BBB. And pharmacologists always have a task: does this drug pass through the BBB? In some cases this is necessary, if we are talking about brain diseases, in others it is indifferent to the patient if the drug does not damage nerve cells, and in others it should be avoided. (NANOPARTICLES, ONCOLOGY).

The sympathetic nervous system is excited and stimulates the functioning of the adrenal medulla - the production of adrenaline; in the pancreas - glucagon - breaks down glycogen in the kidneys to glucose; glucocarticoids produced in the adrenal cortex - provides gluconeogenesis - the formation of glucose from ...)

And yet, with all the diversity of neurons, they can be divided into three groups: afferent, efferent and intercalary (intermediate).

15) Afferent neurons, their functions and structure. Receptors: structure, functions, formation of an afferent volley.