Midbrain. Medial longitudinal bundle Group of nerves of the eye muscles

Bundle system (fasciculi proprii)

Bundle system (fasciculi proprii). Basic bundles spinal cord They consist of short ascending and descending fibers that arise and end in the gray matter of the spinal cord and connect its various segments. These bundles are found in all three white columns of the spinal cord, directly surrounding the gray matter. Some fibers of fasciculi proprii ventralis, lying on the sides of the anterior longitudinal fissure and designated as fasciculus sulco-marginalis, continue directly into the brainstem, where they are called fasciculus longitudinalis medialis or fasc. longitudinalis posterior. The main beams are intended for intraspinal reflexes.

Fasciculus septo-marginalis and fasciculus interfascicularis located in the posterior columns, partly consist of fibers that arise and end in the gray matter of the spinal cord, partly from fibers that form the descending divisions of the posterior nerve roots.

Long pathways in the central nervous system represent a relatively late phase of development and evolution. nervous system vertebrates. More primitive pathways consist of a chain of short neurons. In humans, a system of main bundles is built from such short neurons.

Fasciculus longitudinalis medialis (f. longitudinalis posterior) - medial posterior longitudinal bundle. The medial longitudinal bundle is a bundle of motor coordination fibers running along the entire length brain stem and closely related to the vestibular apparatus.

Fasc. longitudinalis medialis consists mainly of thick fibers that are covered with myelin in a very early stage development, - approximately at the same time with the nerve roots. This bundle exists in almost all vertebrates. In some of the lower vertebrates it is even better expressed than in mammals; it is especially great in amphibians and reptiles. Due to its early myelination and in contrast to the thin, more or less scattered fibers of the tecto-spinal tract located in front of it, this bundle protrudes especially sharply in the brainstem of the uterine infant.

Like a clearly defined bunch of fasc. longitudinalis medialis extends upward to the posterior commissure and the nucleus of the common oculomotor nerve. At this level, it comes into contact with the interstitial nucleus of Cajal, which is usually called the initial nucleus of the longitudinal medial bundle and which is located immediately anterior to the red nucleus. The interstitial nucleus, says Ranson, should not be confused with the nucleus of the posterior commissure (Darshkevich's nucleus), which is located in the midbrain, immediately anterior to the nucleus of the oculomotor nerve. From Darshkevich's nucleus, fibers can also be directed to the medial longitudinal bundle.

Down fasc. longitudinalis medialis can be traced to the intersection of the pyramids, after which it continues into its own bundle (fasciculus proprius) of the anterior columns and stretches along the entire length of the spinal cord.

Changing the position of fasc. longitudinalis medialis, as well as fasc. tecto-spinalis from the ventral, which they have in the spinal cord, to the dorsal, which they have in the oblongata; depends on the fact that immediately anterior to these pathways in the medulla oblongata is the intersection of the medial lemniscus, and even more anterior to the intersection of the pyramidal pathways.

Top section fasc. longitudinalis medialis is placed under the bottom of the Sylvian aqueduct, lying on the sides of the median plane between the lower part of the gray matter surrounding the Sylvian aqueduct, where the motor nuclei of the eye muscles are located, and the reticular formation (formatio reticularis) of the midbrain. In the pons and medulla oblongata, it lies at the bottom of the IV ventricle along the boxes of the median groove. Along the midline, the fibers of the bundle of one side can pass into the bundle of the other side.

A significant part of the fibers of the longitudinal medial tract comes from nerve cells lateral vestibular macaw (nucleus of Deiters). The axons of these cells, having passed through the adjacent sections of the reticular formation, enter the longitudinal medial bundle of the same or opposite side and divide in it into ascending and descending branches. The ascending branches, establishing a connection between the lateral vestibular nucleus and the motor nuclei of the abducens, trochlear and oculomotor nerves, cause the eyeball to respond appropriately to proprioceptive impulses that occur in the semicircular canals. The descending branches, in turn, establish a connection with the motor nucleus of the cranial accessory nerve (XI) and with the anterior horns of the spinal cord. Thus, with the help of these descending fibers, the muscles of the head and trunk also come under the direct control of proprioceptive impulses coming from the semicircular canals. Other fibers included in fasc. longitudinalis medialis, may begin: 1) from cells scattered in the reticular formation of the midbrain, pons and medulla oblongata; 2) from cells located in the sensory nuclei of some of the cranial nerves, mainly trigeminal nerve, and 3) from Cajal interstitial nucleus and Darshkevich nucleus cells.

Latin name: fasciculus longitudinalis medialis.

Where is?

In the brainstem, the MPP is located close to the central line, ventral to the central gray matter, and passes slightly anterior to the nuclei of the oculomotor nerve. In the thickness of the brainstem, the medial longitudinal bundle can be found in any part of the longitudinal section. The MPP originates from the rostral interstitial nucleus of the longitudinal bundle (riMPP). Descending a little lower, bundles from the nucleus of Darkshevich and Kahal join the fibers from riMPP. Thus, the tip of the medial longitudinal bundle resembles a flower bouquet.

Anatomy

Recall that speaking of a separate structure in the brain, we should not forget that the human brain has two hemispheres, two hemispheres. This means that the structure we are describing is also a pair structure. Often, the pairing of brain structures means that the exchange of data between them is carried out due to decussations, jumpers (anastomoses), and special fibers. However, there are exceptions. Among them is the medial longitudinal bundle.

MPP is formed by a group of fibers tightly pressed to each other. The proximity of the fibers of one side with the opposite, allows you to do without switching, jumpers, individual fibers and freely exchange signals.

What is the function?

The main role of the MPP is participation in oculomotor functions. The fibers of the Medial Longitudinal Bundle are connected to the nuclei, which provide a wide variety of movements eyeball. In the MPP, signals flow mainly from the oculomotor innervation, as well as vestibular and auditory ones. Due to this special structure, a number of important functions of the body are carried out. The fibers of some cranial nuclei pour into the medial longitudinal bundle to coordinate the response of the innervated structures.

And how does it work?

A personal command comes from each core and, merging into the MPP, the command is distributed to all fibers connected to the system. To give an example, a MSP can be compared to a section of a freeway. Gathering into a single stream, any signal can turn in the direction it needs.

Pathology

Knowing what functions are provided by the structures, the fibers of which are part of the MPP, it can be assumed that there are violations when this structure is damaged.

Most often, these are various manifestations of oculomotor functions: gaze paresis (the impossibility of simultaneously looking in any direction), strabismus, a symptom of floating eyes (separated movements). All these symptoms are characteristic of the so-called internuclear ophthalmoplegia.

midbrain (mesencephalon)(Fig. 4.4.1, 4.1.24) develops in the process of phylogenesis under the predominant influence of the visual receptor. For this reason, its formations are related to the innervation of the eye. Hearing centers also formed here, which, together with the centers of vision, later grew in the form of four mounds of the roof of the midbrain. With the appearance in higher animals and humans of the cortical end of the auditory and visual analyzers, the auditory and visual centers of the midbrain fell into a subordinate position. At the same time, they became intermediate, subcortical.

With the development of the forebrain in higher mammals and humans through midbrain conduction pathways began to pass, connecting the cortex of the telencephalon with the spinal cord

through the legs of the brain. As a result, in the human midbrain there are:

1. Subcortical centers of vision and nuclei of the nerve
vas that innervates the muscles of the eye.

2. Subcortical auditory centers.

3. All ascending and descending swiping
tracts that connect the cerebral cortex
with the spinal cord.

4. White matter bundles that bind
midbrain with other parts of the central
nervous system.

Accordingly, the midbrain has two main parts: the roof of the midbrain (tectum mesencephalicum), where are the subcortical centers of hearing and vision, and the legs of the brain (cms cerebri), where the conducting paths predominantly pass.

1. The roof of the midbrain (Fig. 4.1.24) is hidden under the posterior end of the corpus callosum and is subdivided by means of two grooves running crosswise - longitudinal and transverse - into four mounds located in pairs.

Upper two mounds (colliculi superiores) are subcortical centers of vision, both lower (colliculi inferiores)- subcortical

Rice. 4.1.24. The brain stem, which includes the midbrain (mesencephalon), hindbrain

(metencephalon) and medulla oblongata (myelencephalon):

a- front view (/-motor root of the trigeminal nerve; 2 - sensitive root of the trigeminal nerve; 3 - basal sulcus of the bridge; 4 - vestibulocochlear nerve; 5 - facial nerve; 6 - ventrolateral sulcus of the medulla oblongata; 7 - olive; 8 - circummolition bundle; 9 - pyramid of the medulla oblongata; 10 - anterior median fissure; // - intersection of pyramidal fibers); b - rear view (/ - pineal gland; 2 - superior tubercles of the quadrigemina; 3 - inferior tubercles of the quadrigemina; 4 - rhomboid fossa; 5 - knee facial nerve; 6 - median fissure of the rhomboid fossa; 7 - superior cerebellar peduncle 8 - middle cerebellar peduncle; 9 - inferior cerebellar peduncle 10 - vestibular area; //- triangle of the hypoglossal nerve; 12 - triangle vagus nerve; 13 - tubercle of the wedge-shaped bundle; 14 - tubercle of tender nucleus; /5 - median sulcus)

hearing centers. The pineal body lies in a flat groove between the superior tubercles. Each hillock passes into the so-called knob of the hillock (brachium colliculum), going laterally, anteriorly and upward to the diencephalon. Upper mound handle (brachium colliculum superiores) goes under the pillow of the thalamus to the lateral geniculate body (corpus geniculatum laterale). Inferior colliculus handle (brachium colliculum inferiores), running along the top edge trigo-pita lemnisci before sulcus lateralis mesencephali, disappears under the medial geniculate body (corpus geniculatum mediale). The named geniculate bodies already belong to the diencephalon.

2. Legs of the brain (pedunculi cerebri) contain
all pathways to the forebrain.
The legs of the brain look like two thick semi-circles
lindric white strands that diverge
from the edge of the bridge at an angle and plunge into
the thickness of the cerebral hemispheres.

3. The cavity of the midbrain, which is the OS
tacoma of the primary cavity of the midcerebral
bubble, looks like a narrow channel and is called
aqueduct of the brain (aqueductus cerebri). He
represents a narrow, ependymal-lined ca
cash 1.5-2.0 cm length connecting III and IV
ventricles. Dorsal aqueduct restrict
is covered by the roof of the midbrain, and ventrally -
cover of the legs of the brain.

On a transverse section of the midbrain, three main parts are distinguished:

1. Roof plate (lamina tecti).

2. Tire (tegmentum), representing
the upper part of the legs of the brain.

3. Ventral part of the legs of the brain, or wasps
pedunculation of the brain (basis pedunculi cerebri).
According to the development of the midbrain under
the influence of the visual receptor in it
we have different kernels related to in
nervation of the eye (Fig. 4.1.25).

The aqueduct of the brain is surrounded by a central gray matter, which in its function is related to the autonomic system. In it, under the ventral wall of the aqueduct, in the tire of the brain stem, the nuclei of two motor cranial nerves are laid - n. oculomotorius(III pair) at the level of the superior colliculus and n. trochlearis(IV pair) at the level of the inferior colliculus. The nucleus of the oculomotor nerve consists of several sections, respectively, of the innervation of several muscles of the eyeball. Medially and posteriorly from it, a small, also paired, vegetative additional nucleus is placed. (nucleus accessorius) and an unpaired median nucleus.

The accessory nucleus and the unpaired median nucleus innervate the involuntary muscles of the eye. (t. ciliaris and t. sphincter pupillae). Above (rostral) the nucleus of the oculomotor nerve in the tegmentum of the brain stem is the nucleus of the medial longitudinal bundle.

Rice. 4.1.25. Nuclei and connections of the midbrain and its stem (according to Leigh, Zee, 1991):

1 - lower tubercles; 2 - intermediate core of Cajal; 3 - medial longitudinal bundle; 4 - reticular formation of the medulla oblongata; 5 - Darkshevich core; 6 - n. perihypoglos-sal; 7- rostral intermediate medial longitudinal bundle; 8 - superior tubercles; 9 - paramedian reticular formation of the bridge; III, IV, VI - cranial nerves

Lateral to the aqueduct of the brain is the nucleus of the mesencephalic tract of the trigeminal nerve (nucleus mesencephalicus n. trigemini).

Between the base of the brain stem (basis pedunculi cerebralis) and tire (tegmentum) black matter is located (substantia nigra). In the cytoplasm of neurons of this substance, a pigment, melanin, is found.

From the tegmentum of the midbrain (tegmentum mesencephali) departs the central tire track (tractus tegmentalis centralis). It is a projection descending path that contains fibers coming from the thalamus, globus pallidus, red nucleus, and the reticular formation of the midbrain in the direction of the reticular formation and olive of the medulla oblongata. These fibers and nuclear formations belong to the extrapyramidal system. Functionally, the substantia nigra also belongs to the extrapyramidal system.

Located ventrally from the substantia nigra, the base of the brain stem contains longitudinal nerve fibers descending from the cerebral cortex to all the underlying parts of the central nervous system. (tractus corticopontinus, corticonuclearis, cortico-spinalis and etc.). The tire, located dorsally from the black substance, contains mainly

Anatomy of the brain

significantly ascending fibers, including the medial and lateral loops. As part of these loops, all sensory pathways ascend to the large brain, with the exception of the visual and olfactory ones.

Among the nuclei of gray matter, the most significant nucleus is the red nucleus. (nucleus ruber). This elongated formation extends in the tegmentum of the brain stem from the hypothalamus of the diencephalon to the inferior colliculus, where an important descending pathway begins from it. (tractus rubrospinalis), connects the red nucleus with the anterior horns of the spinal cord. The bundle of nerve fibers after exiting the red nucleus intersects with a similar bundle of fibers of the opposite side in the ventral part of the median suture - the ventral decussation of the tire. The red nucleus is a very important focal point of the extrapyramidal system. Fibers from the cerebellum pass to it, after they cross under the roof of the midbrain. Thanks to these connections, the cerebellum and the extrapyramidal system, through the red nucleus and the red nuclear-spinal tract extending from it, influence the entire striated muscles.

The reticular formation also continues into the tegmentum of the midbrain. (formatio reticularis) and a longitudinal medial bundle. The structure of the reticular formation is described below. It is worth dwelling in more detail on the medial longitudinal bundle, which is of great importance in the functioning of the visual system.

Medial longitudinal bundle(fasciculus longitudinalis medialis). The medial longitudinal bundle consists of fibers coming from the nuclei of the brain various levels. It extends from the rostral midbrain to the spinal cord. At all levels, the bundle is located near the midline and somewhat ventral to the Sylvian aqueduct, the fourth ventricle. Below the level of the nucleus of the abducens nerve, most fibers are descending, and above this level, ascending fibers predominate.

The medial longitudinal bundle connects the nuclei of the oculomotor, trochlear, and abducens nerves (Fig. 4.1.26).

The medial longitudinal bundle coordinates the activity of the motor and four vestibular nuclei. It also provides intersegmental integration of movements associated with vision and hearing.

Through the vestibular nuclei, the medial bundle has extensive connections with the flocculent-nodular lobe of the cerebellum. (lobus flocculonodularis), which coordinates the complex functions of eight cranial and spinal nerves (optic, oculomotor, trochlear, trigeminal, abducens,

Rice. 4.1.26. Communication between the nuclei of the oculomotor, trochlear and abducens nerves using the medial longitudinal bundle

facial, vestibulocochlear nerves).

Descending fibers form mainly in the medial vestibular nucleus (nucleus vestibularis medialis), reticular formation, superior colliculus, and intermediate nucleus of Cajal.

Descending fibers from the medial vestibular nucleus (crossed and non-crossed) provide monosynaptic inhibition of the upper cervical neurons in the labyrinth regulation of the position of the head relative to the body.

Ascending fibers originate from the vestibular nuclei. They are projected onto the nuclei of the oculomotor nerves. The projection from the superior vestibular nucleus passes in the medial longitudinal bundle to the trochlear and dorsal oculomotor nucleus on the same side (neurons of the motor of the inferior rectus muscle of the eye).

Ventral parts of the lateral vestibular nucleus (nucleus vestibularis lateralis) are projected onto the opposite nuclei of the abducens and trochlear nerves, as well as onto a part of the nuclei of the oculomotor complex.

Mutual connections of the medial longitudinal bundle are axons of intercalary neurons in the nuclei of the oculomotor and abducens nerves. The intersection of the fibers occurs at the level of the nucleus of the abducens nerve. There is also a bilateral projection of the oculomotor nucleus on the nucleus of the abducens nerve.

Interneurons oculomotor nerves and neurons of the superior colliculi of the quadrigemina are projected onto the reticular formation. The latter, in turn, project onto the cerebellar vermis. In the reticular

Chapter 4. BRAIN AND EYE

Formations are switching fibers, heading from the supranuclear structures to the cerebral cortex.

The abducens internuclear neurons project mainly to the contralateral oculomotor neurons of the internal and inferior rectus muscles.

Superior tubercles (knolls) of the quadrigemina(collicilus superior)(Fig. 4.1.24-4.1.27).

The superior colliculi of the quadrigemina are two rounded elevations located on the dorsal surface of the midbrain. They are separated from each other by a vertical groove containing the epiphysis. The transverse furrow separates the superior colliculi from the inferior colliculi. Above the upper hillocks is the visual tubercle. Above the midline lies the great vein of the brain.

The superior colliculi of the quadrigemina have a multilayer cellular structure(see "Visual Path"). Numerous nerve tracts approach and exit from them.

Each colliculus receives an accurate topographic projection of the retina (Fig. 4.1.27). The dorsal part of the quadrigemina is mostly sensory. It is projected onto the outer geniculate body and the pillow.

Pillow thalamus

Pretectal area

Rice. 4.1.27. Schematic representation of the main connections of the superior tubercles of the quadrigemina

The ventral portion is motorized and projects to motor subthalamic areas and the brainstem.

The superficial layers of the quadrigemina carry out the processing of visual information and, together with the deep layers, provide the orientation of the head and eyes in the process of determining new visual stimuli.

Stimulation of the superior colliculus in a monkey causes saccadic movements, the amplitude and direction of which depend on the location of the stimulus. Vertical saccades occur with bilateral stimulation.

Surface cells respond to stationary and moving visual stimuli. Deep cells usually fire before the saccade.

The third type of cell combines information about the position of the eye with information received from the retina. Thanks to this, the necessary position of the eye relative to the head is controlled and specified. This signal is used for

reproduction of a saccade, the direction of which is turned towards a visual target. Superficial and deep layers can function independently.

The inferior colliculi are part of the auditory pathway.

The midbrain tegmentum is located anterior or ventral to the colliculi. In the longitudinal direction, between the roof and the tire of the midbrain, the Sylvian aqueduct passes. The midbrain tegmentum contains numerous descending and ascending fibers related to the somatosensory and motor systems. In addition, there are several nuclear groups in the tire, among which the nuclei III and IV pairs of cranial nerves, the red nucleus, as well as the accumulation of neurons belonging to the reticular formation. The midbrain tegmentum is considered as a central accumulation of motor and reticular fibers that run from the diencephalon to the medulla oblongata.

Ventral or anterior to the midbrain tegmentum is a large paired bundle of fibers - the brain stem, which contains mainly thick descending motor fibers originating in the cerebral cortex. They transmit motor efferent impulses from the cortex to the nuclei of the cranial nerves and the nuclei of the bridge (tractus corticobulbaris sen corticinuclearis), as well as to the motor nuclei of the spinal cord (tractus corticispinalis). Between these important bundles of fibers on the anterior surface of the midbrain and its tegmentum is a large nucleus of pigmented nerve cells containing melanin.

The pretectal region receives adductor fibers from the optic tract (see Fig. 4.1.27). It also receives occipital and frontal corticotectal fibers to aid in vertical gaze, vergence, and accommodation of the eye. The neurons of this area selectively respond to visual information, taking into account changes in the localization of the object image on both retinas.

The pretectal region also contains pupillary reflex synapses. Some of the efferent fibers intersect in the area of ​​gray matter located around the Sylvian aqueduct. The fibers are sent to the small cell nuclei of the oculomotor nerve, which control the pupillomotor fibers.

It is also necessary to point out the presence of three tegmental pathways, which are of great functional importance. This is the lateral spinothalamic tract. (tractus spinothalamicus lateralis), medial lemniscal pathway (medial lemniscus; lemniscus medialis) and medial

Anatomy of the brain

New longitudinal bundle. The lateral spinal-thalamic pathway carries afferent pain fibers and is located in the tegmentum of the midbrain from the outside. The medial lemniscus provides the transmission of sensory and tactile information, as well as information about the position of the body. It is located in the region of the bridge medially, but is displaced laterally in the midbrain. It is a continuation of the medial loops. The lemniscus connects the thin and wedge-shaped nuclei with the nuclei of the thalamus.

• vestibular system
• Medial longitudinal bundle

Normal eye movements are always simultaneous and combined. The association of movements of the eyeballs requires not only the preservation of the morphology and functions of the nuclear apparatus of the cranial nerves involved in providing such movements, the roots, trunks of these nerves and eye muscles. It also requires the integrity of the associative links between the cell groups (nuclei) included in the oculomotor apparatus, their adequate interaction with the vestibular system. This requires the preservation of the function of the medial longitudinal bundles and the structures of the reticular formation associated with them, subcortical and cortical oculomotor centers.

vestibular system, coordinating the work of the oculomotor apparatus, is actively involved in ensuring the synchronization of gaze, coordinating it with the position in space of the body, mainly the head. When the vestibular receptor apparatus, vestibular nerves and their nuclei are affected, vestibular reflexes. Irritation of the vestibular structures can cause excessive involuntary eye movements like nystagmus, tonic muscle reactions, coordination disorders, dizziness, autonomic reactions.

vestibular system

The threshold of the labyrinth (labyrinthine vestibule) - part of the inner ear - connects the semicircular canals and the cochlea. Three semicircular bone canals related to the vestibular system are located in three mutually perpendicular planes and are interconnected. These channels, the vestibule and the cochlear duct connecting them are located in the pyramid of the temporal bone.

They contain a membranous labyrinth (labyrinthus membranaceus) consisting of membrane tissue, including three membrane semicircular ducts (ductus semicirculares membranaceus), as well as an otolith apparatus - an elliptical and spherical sac ki (sacculus et utriculus). The membranous labyrinth is surrounded by perilymph, which is an ultrafiltrate of cerebrospinal fluid. It is filled with endolymph, probably secreted by the cells of the labyrinth itself.

Receptors of the vestibular system are located in the semicircular ducts and in the otolith apparatus of the inner ear. All three semicircular ducts end in ampullae containing receptor hair cells that make up the ampullar ridges. These scallops are embedded in the gelatinous substance, which forms a dome above them. The receptor hair cells of the scallops are sensitive to the movement of the endolymph in the semicircular ducts of the canals and respond to changes in the speed of its movement - acceleration and deceleration. In this regard, they are called kinetic receptors.

Receptors of the otolithic apparatus are concentrated in areas called spots (maculae). In one of the bags, such a spot occupies a horizontal position, in the other - a vertical position. The receptor hair cells of each spot are embedded in the gelatinous tissue containing sodium carbonate crystals - otoliths, a change in the position of which causes irritation of the receptor cells, while nerve impulses appear in them, signaling the position of the head in space.

From the peripheral apparatus of the vestibular system, impulses follow the dendrites of the first neurons of the vestibular pathways to the vestibular mind (ganglion vestibularis, or Scarpe's node) - an analogue of the spinal nodes located in the internal auditory canal. It contains the bodies of the first neurons of the pathway of vestibular impulses. From here, vestibular impulses follow the axons of the same nerve cells that make up the vestibular portion VIII cranial nerve (n. vestibulocochlearis). VIII nerve leaves temporal bone through internal ear canal, crosses the lateral cistern of the pons and enters the brainstem in the lateral part of the sulcus that delimits the basal surfaces of the pons and medulla oblongata.

Entering the brain stem vestibular portion of the VIII nerve divided into ascending and descending parts.

• The ascending part ends mainly in the cells of the superior vestibular nucleus of Bechterew (nucleus superior). Some ascending fibers, bypassing Bekhterev's nucleus, enter the cerebellar vermis through the inferior cerebellar peduncle and end in its nuclei.
• The descending fibers of the vestibular portion VIII terminate in the triangular medial vestibular nucleus of Schwalbe (nucleus mediais) and the lateral nucleus of Deiters (nucleus lateralis), as well as in the most caudally located nucleus of the descending root - the lower nucleus of Roller (nucleus inferior).

The bodies of the second neurons of the vestibular analyzer are located in the vestibular nuclei, the axons of which then follow in different directions, providing the formation of numerous vestibular connections. A significant part of the axons of the nerve cells of the superior, lateral, medial and inferior vestibular nuclei are directly or indirectly involved in the formation of the vestibular longitudinal bundle. They go up, partially pass to the opposite side and end at the cells of the nuclei of the III, IV and VI nerves, which provide innervation of the external eye muscles of both eyes.

The presence of vestibulo-oculomotor connections creates the possibility of synchronizing the tension of the striated eye agonist muscles and, at the same time, reducing the tension of the antagonist muscles, which is necessary to maintain the friendliness of the movements of the eyeballs and gaze with changes in body position. The axons of the vestibular cells, which take a downward direction, are involved in the formation of the vestibulospinal tracts, which in the cervical spinal cord are located in the medial part of its anterior cords and here enter into synaptic connections with the motor neurons of the anterior horns. All this leads to the fact that the vestibular system is actively involved in ensuring coordination between the position of body parts in space and the direction of gaze.

Medial longitudinal bundle

The development of strabismus and diplopia is often the result of disorganization of the coordinating function medial longitudinal bundle , which plays an important role in ensuring the association of movements of the eyeballs.

The medial (or posterior) longitudinal bundle (fasciculis longitudinalis medialis) is a paired formation, complex in composition and function, located in the tegmentum of the brain stem, near the midline, under the aqueduct of the brain and the bottom of the rhomboid fossa of the IV ventricle. The medial longitudinal bundle plays an important role in ensuring the combined movements of the eyeballs (gaze). Starting, as is commonly believed, from the posterior commissural nucleus of Darkshevich and the intermediate nucleus of Kohal, located near the border between the upper part of the trunk and the diencephalon, the medial longitudinal bundle descends as part of the trunk tire to cervical spinal cord.

At the same time, part of the fibers coming from the Darkshevich nucleus enters the medial longitudinal bundle of the same side, and some first passes through the posterior commissure of the brain to the other side, after which it is included in the medial longitudinal bundle of the opposite side. From here, the medial longitudinal bundles pass through the tegmentum of the brainstem throughout its entire length, after which they penetrate into the anterior cords of the spinal cord. In the spinal cord, they end at the cells of its anterior horns, mainly at the cervical level, as well as in motor neurons located in the ventrolateral sections of the C 2 -C 6 segments of the spinal mole and constituting the nuclear apparatus of the spinal portion of the accessory (XI) cranial nerves.

The medial longitudinal bundles are especially developed at the level of the midbrain and pons. They can be considered as a set of nerve fibers belonging to various systems, consisting of descending, ascending and transverse associative pathways. These pathways connect paired cell formations of the brain stem, in particular, the nuclei of the first cranial (III, IV and VI), which provide eye movements, the vestibular nuclei and the adjacent sections of the reticular formation, as well as the motor neurons of the anterior horns of the cervical spinal cord and accessory (XI) nerves.

Normally, the excitation of any of the eye muscles is never isolated. The contraction of one muscle of the eye in order to change its position is always accompanied by a reaction of other muscles of both eyeballs, which ensures the combined movements of both eyes. So, when the gaze is turned to the left, due to the contraction of the external rectus muscle of the left eye, which occurs under the influence of the left abducens nerve, the right eye also turns to the left. This movement is provided mainly by its internal rectus muscle, innervated by the right oculomotor nerve, which in this case manifests itself as an agonist of the external rectus muscle of the opposite eye.

Simultaneously and necessarily in accordance with the law reciprocal innervation Sherrington, relaxation of muscles occurs, which are antagonists in relation to contracting muscles.
It can be recognized that with any change in the direction of gaze, almost all oculomotor muscles take part in one way or another. Such synchrony of eye movements is possible due to the associative connections of the nuclei of the cranial nerves that are part of the medial longitudinal bundle, innervating the external eye muscles and, thus, taking one or another part in the implementation of gaze movement. Associative eye movements provide direct and feedback connections between the nuclei of the nerves innervating the eye muscles, as well as their bilateral connections with the vestibular nuclei, with the nuclei of the adjacent sections of the reticular formation and with other nervous structures that affect the state of the oculomotor apparatus.

Thus, the medial longitudinal bundles form the anatomical basis for the combined contractions and relaxation of the eye muscles and the resulting synchronous, simultaneous movements of both eyes. To a large extent, due to the medial longitudinal fascicles, normal movements of the eyeballs always occur simultaneously, in combination, friendly. Any change in the direction of gaze when tracking a moving object is manifested by simultaneous synchronous eye movements (eye conjugation phenomenon), which ensures their fixation on a specific object, accompanied by its combined reflection in the optical center (in the central fovea of ​​the spot) of the retinas of both eyes.

R. Bing and R. Brückner (1959) recognized that the axons of the vestibular nuclei (mainly the superior nucleus of Bechterew, the medial nucleus of Schwalbe and the lateral nucleus of Deiters) occupy an important place in the composition of the medial longitudinal bundle, making a partial decussation and participating in the formation of bilateral connections, providing labyrinth reflexes. These reflexes play a leading role in ensuring a certain direction of gaze and its fixation on an object during changes in the position of the body, especially with changes in the position of the head.

Head movements lead to the fact that in the receptor structures of the vestibular apparatus (in the membranous labyrinth, in the otolith apparatus) impulses arise that are transmitted to the vestibular nuclei. Synchronously with the change in muscle tone, aimed at keeping the head in the given position, through the medial longitudinal bundle, a reaction of the eye muscles occurs, providing tracking of the object of interest, while the gaze is fixed on it, and when the position of the head changes, it will mix in the opposite direction. In the case of a fast movement of an object, the gaze fixed on it periodically jumps in the opposite direction. After that, eye tracking of the object continues. The combined eye movements that occur in such cases are manifestations of optokinetic nystagmus.

It is assumed that there are associative links between the structures of the medial longitudinal bundle and the trigeminal nerve, which ensure the conduction of impulses of pain, tactile and proprioceptive sensitivity from the tissues of the eye and its appendages, in particular from the eye muscles. They take part in the formation of reflex arcs of the corneal and conjunctival reflexes, as well as optokinetic reflexes, which are based on a change in the position of the gaze fixed on a moving object through the medial fibers of the medial longitudinal bundles.

An example of an optokinetic reflex is the so-called railway nystagmus, in which the gaze of a passenger looking out the window of a moving train is fixed for some time on objects located outside the window and follows them, gradually shifting to the side opposite to the movement of the train, and when they disappear, it abruptly returns to starting position.

Thus, the medial bundle includes the axons of the nerve cells that make up the nuclei of the III, IV and VI cranial nerves, the vestibular portion of the VIII cranial nerve, the axons of the nerve cells of the Darkshevich nucleus and the intermediate Kochal nucleus. In addition, the medial bundle has connections with the nuclei of the colliculi of the quadrigemina, the trigeminal nerve and the reticular formation, as well as with the subcortical gaze centers, the superior olive, the cerebellum and the basal ganglia.

The axons of the cells of the reticular formation of the brain stem, which take part in the formation of the medial longitudinal bundles, have bilateral connections with various parts of the central nervous system. Thus, the reticular system affects the functional state of the vestibulo-oculomotor connections and, participating in the coordination of visual, vestibular and proprioceptive impulses, maintains the associated nature of the activity of the oculomotor apparatus. There is reason to say that damage to the reticular formation can cause various disorders of the functional state of the oculomotor apparatus in the form of ocular ataxia, pathological nystagmus, and difficulties in fixing a moving object with the gaze.
The nuclei of the oculomotor nerves through vestibular structures and cells of the reticular formation are associated with the cerebellum, which, along with influencing the state of the visual and proprioceptive systems, is involved in providing eimetry, correcting active movements by extinguishing inertia, and also providing the most rational regulation of the tone of reciprocal mice.

All brain structures that direct nerve signals directly or indirectly to the medial longitudinal bundle directly or indirectly affect the functions of the nuclei of III, IV and VI cranial nerves. Some of these structures, primarily the vestibular nuclei, the nuclei of Darkshevich and Cajal, the nuclei of the anterior hills of the quadrigemina, other subcortical oculomotor centers are usually considered as supranuclear. The implementation of gaze reactions depends on the impulses emanating from them, which can be influenced by other supranuclear influences: optical, vestibular, acoustic, proprioceptive, tactile and pain stimuli.

Thus, gaze movements depend on the state of many nervous structures, primarily on those that are involved in the formation of the medial longitudinal bundle. The association of eye movements is possible only if the medial longitudinal fasciculus and the formations of the nervous system that form it are preserved. The defeat of the medial longitudinal bundle leads to the emergence of various oculomotor disorders, the nature of which depends on the localization and prevalence of the pathological process. Possible various forms disorders of combined eye movements (gaze), pathological forms of nystagmus, ophthalmoparesis or ophthalmoplegia.

The red nucleus is the main motor coordination center of the extrapyramidal system. It has numerous connections with the cerebral cortex, with the striopallidar system, with the thalamus, with the subthalamic region and with the cerebellum. Nerve impulses arriving at the neurons of the red nucleus from the cerebral cortex, nuclei of the striopallidar system and nuclei of the diencephalon, after appropriate processing, follow the red nuclear-spinal path, which ensures the execution of complex habitual movements (walking, running), making these movements plastic, helping to maintain a certain posture for a long time, as well as causing the maintenance of skeletal muscle tone.

From the neurons of the cerebral hemispheres, mainly from the frontal lobe, axons form the cortical-striatal tract, which passes through the anterior leg of the internal capsule. Only a small part of the fibers of this tract ends directly on the small multipolar cells of the red nucleus of the midbrain. Most of the fibers go to the nuclei of the striatal system (basal nuclei of the brain), in particular to the caudate nucleus and putamen. From the neurons of the striatal system to the red nucleus, the striatal-red nuclear pathway is directed.

From the structures of the diencephalon, neurons of the medial nuclei of the thalamus (subcortical sensory center of the extrapyramidal system), neurons of the pale ball (pallidar system) and neurons of the posterior nuclei of the hypothalamus are connected with the red nucleus. The axons of the cells of the nuclei of the diencephalon are collected in the thalamo-red nuclear bundle, which ends on the cells of the red nucleus and black substance. Neurons of the black matter also have connections with the red nucleus.

Nerve impulses coming to the neurons of the red nucleus from the cerebellum carry out the so-called corrective activity. They ensure the performance of fine targeted movements and prevent inertial manifestations during movements.

The cerebellum is connected to the red nuclei through a two-neuron pathway - the cerebellar-red nuclear tract. The first neurons of this path are the cells of the cortex of the cerebellar hemispheres, the axons of which end in the dentate nucleus. The second neurons are cells of the dentate nucleus, the axons of which leave the cerebellum through the superior peduncles. The cerebellar-red-nuclear tract enters the midbrain, at the level of the lower colliculus, crosses with the same tract of the opposite side (Wernecking's cross) and ends on the cells of the red nucleus (Fig. 4.10).

Rice. 4.10.

1 - gear-red nuclear path; 2 - cerebellum; 3 - cerebellar cortex; 4 - dentate nucleus; 5 - cervical segment; 6 - lumbar segment; 7 - motor nuclei of the anterior horns of the spinal cord; 8 - red nuclear-spinal path; 9 - bridge; 10 - red core; 11 - midbrain

From the neurons of each red nucleus, the descending red-nuclear-spinal path (Monakov's bundle) and the red-nuclear-nuclear path begin, which immediately pass to the opposite side in the midbrain tegmentum and form the anterior decussation of the tegmentum (Forel cross).

The red nuclear pathway passes through the tegmentum of the brain stem and ends at the motor neurons of the motor nuclei of the cranial nerves. The axons of motor neurons of the nuclei of the cranial nerves are sent to the skeletal muscles of the eyeball, head, pharynx, larynx and upper esophagus, providing their efferent innervation.

The red nuclear-spinal tract runs in the lateral funiculus of the spinal cord. In the latter, it is located anterior to the lateral cortico-spinal tract. Gradually, the bundle of fibers becomes thinner, as the axons end segment by segment on the motoneurons of the motor nuclei of the anterior horns of the spinal cord of their side. Axons of motor neurons leave the spinal cord as part of the anterior roots spinal nerves, and then, as part of the nerves themselves and their branches, they are sent to the skeletal muscles.

performs unconditioned reflex motor reactions in response to sudden strong visual, auditory, tactile and olfactory stimuli. The first neurons of the roof-spinal tract are located in the superior colliculi of the midbrain - the subcortical integration center of the midbrain (Fig. 4.11). Information enters this integration center from the subcortical centers of vision (the nucleus of the superior colliculus), subcortical center hearing (the core of the lower colliculus), the subcortical center of smell (the core of the mastoid body) and collaterals from the pathways of general sensitivity (spinal, medial and trigeminal loops).

The axons of the first neurons go ventrally and upward, bypass the central gray matter of the midbrain and pass to the opposite side, forming the posterior tegmental decussation (Meinert's decussation). Further, the tract passes in the dorsal part of the bridge next to the medial longitudinal bundle. In the course of the tract, fibers depart in the brainstem, which end on the motor neurons of the motor nuclei of the cranial nerves. These fibers are combined under the name of the roof-nuclear bundle. They provide protective reactions involving the muscles of the head and neck.

In the region of the medulla oblongata, the roof-spinal tract approaches the dorsal surface of the pyramids and goes to the anterior funiculus of the spinal cord. In the spinal cord, it occupies the most medial part of the anterior funiculus, limiting the anterior median fissure.

The roof-spinal tract is traced throughout the entire spinal cord. Gradually thinning, it gradually gives off branches to the motoneurons of the motor nuclei of the anterior horns of the spinal cord of its side. Axons of motor neurons conduct nerve impulses to the muscles of the trunk and limbs.

Rice. 4.11.

1 - superior colliculus of the midbrain; 2 - rear cross tire; 3 - roof-spinal path; 4 - motor nuclei of the anterior horns of the spinal cord; 5 - lumbar segment; 6 - cervical segment; 7 - medulla oblongata; 8 - midbrain

When the roof-spinal tract is damaged, starting reflexes, reflexes to sudden sound, auditory, olfactory and tactile irritations disappear.

3. Reticular-spinal tract ensures the implementation of complex reflex acts (respiratory, grasping movements, etc.), requiring the simultaneous participation of many groups of skeletal muscles. Therefore, it performs a coordinating role in these movements. The reticular-spinal tract conducts nerve impulses that have an activating or, conversely, inhibitory effect on the motor neurons of the motor nuclei of the anterior horns of the spinal cord. In addition, this pathway transmits impulses that provide skeletal muscle tone.

The first neurons of the reticular-spinal tract are located in the reticular formation of the brain stem. The axons of these neurons go in a downward direction. In the spinal cord, they form a bundle, which is located in the anterior funiculus. The bundle is well expressed only in the cervical and upper thoracic regions of the spinal cord. Segmentally, it becomes thinner, giving fibers to the gamma motor neurons of the motor nuclei of the anterior horns of the spinal cord. The axons of these neurons travel to the skeletal muscles.

• 4. Vestibulo-spinal tract provides unconditioned reflex motor acts when changing the position of the body in space. The vestibulospinal tract is formed by the axons of the cells of the lateral and inferior vestibular nuclei (the nuclei of Deiters and Roller). In the medulla oblongata, it is located in the dorsal region. In the spinal cord, it passes at the border of the lateral and anterior cords, therefore it is penetrated by horizontally oriented fibers of the anterior roots of the spinal nerves. The fibers of the vestibulo-spinal tract end in segments on the motor neurons of the motor nuclei of the anterior horns of the spinal cord. The axons of motor neurons as part of the roots of the spinal nerves leave the spinal cord and go to the skeletal muscles, providing a redistribution of muscle tone in response to a change in body position in space.
• 5. Olivo-spinal tract provides unconditional reflex maintenance of the tone of the muscles of the neck and motor acts aimed at maintaining balance.

The olivo-spinal tract starts from the neurons of the inferior olive nucleus of the medulla oblongata. Being a phylogenetically new formation, the inferior olive nucleus has direct connections with the cortex of the frontal hemispheres (cortical-olive path), with the red nucleus (red-nuclear-olive path) and with the cortex of the cerebellar hemispheres (olive-cerebellar path). The axons of the cells of the inferior olive nucleus are assembled into a bundle - the olive-spinal tract, which runs in the anteromedial section of the lateral funiculus. It can be traced only at the level of the six upper cervical segments of the spinal cord.

The fibers of the olivo-spinal tract terminate in segments on the motor neurons of the motor nuclei of the anterior horns of the spinal cord, the axons of which, as part of the anterior roots of the spinal nerves, leave the spinal cord and go to the muscles of the neck.

6. Medial longitudinal bundle performs coordinated movements of the eyeballs and head. This function is necessary to maintain the balance of the body. The performance of this function becomes possible only as a result of a morphofunctional relationship between nerve centers, providing innervation of the muscles of the eyeball (motor nuclei of the III, IV and VI pairs of cranial nerves), centers responsible for the innervation of the neck muscles (motor nucleus of the XI pair and motor nuclei of the anterior horns of the cervical segments of the spinal cord), the center of balance (Deiters' nucleus) . The work of these centers is coordinated by the neurons of large nuclei of the reticular formation - the interstitial nucleus (Kahal's nucleus) and the nucleus of the posterior commissure (Darkshevich's nucleus).

The interstitial nucleus and the nucleus of the posterior commissure are located in the rostral midbrain in its central gray matter. The axons of the neurons of these nuclei form a medial longitudinal bundle that runs under the central gray matter near the midline. Without changing its position, it continues in the dorsal part of the bridge and deviates ventrally in the medulla oblongata. In the spinal cord, it is located in the anterior funiculus, in the angle between the medial surface of the anterior horn and the anterior white commissure. The medial longitudinal fasciculus is traced only at the level of the upper six cervical segments.

From the medial longitudinal bundle, fibers are directed to the motor nucleus of the oculomotor nerve, which innervates most of the muscles of the eyeball. Further, within the midbrain, from the composition of the medial longitudinal bundle, fibers are sent to the neurons of the motor nucleus of the trochlear nerve of the side. This nucleus is responsible for the innervation of the superior oblique muscle of the eyeball.

In the bridge, the axons of the cells of the nucleus of Deiters (VIII pair) enter the medial longitudinal bundle, which go in an ascending direction to the neurons of the interstitial nucleus. Fibers depart from the medial longitudinal bundle to the neurons of the motor nucleus of the abducens nerve (VI pair), which is responsible for the innervation of the lateral rectus muscle of the eyeball. And, finally, within the medulla oblongata and spinal cord from the medial longitudinal bundle, the fibers are sent to the neurons of the motor nucleus of the accessory nerve (XI pair) and the motor nuclei of the anterior horns of the six upper cervical segments responsible for the function of the neck muscles.

In addition to the general coordination of the work of the muscles of the eyeball and the head, the medial longitudinal bundle plays an important integrative role in the activity of the muscles of the eye. By communicating with the cells of the nucleus of the oculomotor and abducens nerves, it ensures the coordinated function of the external and internal rectus muscles of the eye, which manifests itself in a combined turn of the eyes to the side. In this case, there is a simultaneous contraction of the lateral rectus muscle of one eye and the medial rectus muscle of the other eye.

With damage to the interstitial nucleus or medial longitudinal bundle, there is a violation of the coordinated work of the muscles of the eyeball. Most often, this manifests itself in the form of nystagmus (frequent contractions of the muscles of the eyeball, directed in the direction of movement, when the gaze stops). Nystagmus can be horizontal, vertical, and even rotatory (rotational). Often these disorders are supplemented by vestibular disorders (dizziness) and vegetative disorders (nausea, vomiting, etc.).

7. Rear longitudinal beam carries out connections between the vegetative centers of the brain stem and spinal cord.

The posterior longitudinal bundle (Schütze bundle) originates from the cells of the posterior nuclei of the hypothalamus. The axons of these cells unite into a bundle only at the border of the diencephalon and midbrain. Further, it passes in close proximity to the aqueduct of the midbrain. Already in the midbrain, part of the fibers of the posterior longitudinal bundle is directed to the accessory nuclei of the oculomotor nerve. In the region of the bridge, fibers depart from the posterior longitudinal bundle to the lacrimal and superior salivary nuclei of the facial nerve. In the medulla, fibers branch off to the inferior salivary nucleus of the glossopharyngeal nerve and the dorsal nucleus of the vagus nerve.

In the spinal cord, the posterior longitudinal bundle is located in the form of a narrow ribbon in the lateral funiculus, next to the lateral cortical-spinal tract. The fibers of the Schütze bundle end in segments on the neurons of the intermediate-lateral intermediate nuclei, which are the autonomic sympathetic centers of the spinal cord.

Only a small part of the fibers of the posterior longitudinal bundle separates at the level of the lumbar segments and is located near the central canal. This bundle is called the near-ependymal. The fibers of this bundle end on the neurons of the sacral parasympathetic nuclei.

The axons of the cells of the parasympathetic and sympathetic nuclei leave the brainstem or spinal cord as part of the cranial or spinal nerves and are sent to internal organs, vessels and glands. Thus, the posterior longitudinal bundle plays a very important integrative role in the regulation of vital body functions.