Midbrain. Medial longitudinal fasciculus Posterior longitudinal fasciculus

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Midbrain(mesencephalon) develops from the mesencephalon and is part of the brain stem. On the ventral side it is adjacent to the posterior surface of the mastoid bodies in front and the anterior edge of the bridge behind (). On the dorsal surface, the anterior border of the midbrain is the level of the posterior commissure and the base of the pineal gland (epiphysis), and the posterior border is the anterior edge of the medullary velum. The midbrain includes the cerebral peduncles and the roof of the midbrain (Fig. 3.27; Atl.). The cavity of this part of the brain stem is brain aqueduct - a narrow canal that communicates below with the fourth ventricle, and above with the third (Fig. 3.27). In the midbrain there are subcortical visual and auditory centers and pathways that connect the cerebral cortex with other brain structures, as well as pathways that transit through the midbrain and its own pathways.

1 – third ventricle;
2 – epiphysis (retracted);
3 – thalamic cushion;
4 – lateral geniculate body;
5 – handle of the superior colliculus (6);
7 – leash;
8 – cerebral peduncle;
9 – medial geniculate body;
10 – inferior colliculus and
11 – his handle;
12 – bridge;
13 – superior medullary velum;
14 – superior cerebellar peduncle;
15 – fourth ventricle;
16 – lower cerebellar peduncles;
17 – middle cerebellar peduncle;
IV – cranial nerve root

Quadrigemina, or roof of the midbrain

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Four Hills, or roof of the midbrain (tectum mesencephali)(Fig. 3.27) is divided into superior and inferior colliculi by grooves perpendicular to each other. They are covered by the corpus callosum and the cerebral hemispheres. On the surface of the mounds there is a layer of white matter. Below it, in the superior colliculus, lie layers of gray matter, and in the lower colliculus, the gray matter forms nuclei. Some pathways end and begin from gray matter neurons. The right and left colliculi in each colliculus are connected by commissures. From each hillock extend laterally handles of mounds, which reach the geniculate bodies of the diencephalon.

Superior colliculus

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Superior colliculus contains centers of orienting reflexes to visual stimuli. The fibers of the optic tract reach the lateral geniculate bodies, and then some of them along the handles of the upper mounds continues into the superior colliculi, the rest of the fibers go to the thalamus.

Inferior colliculus

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Inferior colliculus serves as the center of orienting reflexes to auditory stimuli. Handles extend forward and outward from the mounds, ending at the medial geniculate bodies. The mounds receive some of the fibers lateral loop the rest of its fibers go as part of the handles of the lower colliculi to the medial geniculate body.

Tectospinal tract

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Originates from the roof of the midbrain tectospinal tract. Its fibers after cross in the tegmentum of the midbrain they go to the motor nuclei of the brain and to the cells of the anterior horns of the spinal cord. The pathway carries efferent impulses in response to visual and auditory stimuli.

Preopercular nuclei

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At the border of the midbrain and diencephalon lie preopercular(pretectal) kernels, having connections with the superior colliculus and parasympathetic nuclei of the oculomotor nerve. The function of these nuclei is the synchronous reaction of both pupils when the retina of one eye is illuminated.

Brain stems

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Pedunculi cerebri occupy the anterior part of the midbrain and are located above the pons. Between them, the roots of the oculomotor nerve (III pair) appear on the surface. The legs consist of a base and a tegmentum, which are separated by highly pigmented cells of the substantia nigra (see Atl.).

IN base of the legs passes a pyramidal path consisting of corticospinal, traveling through the pons to the spinal cord, and corticonuclear, the fibers of which reach the neurons of the motor nuclei of the cranial nerves located in the area of ​​the fourth ventricle and aqueduct, as well as cortical-pontine pathway, ending on the cells of the base of the bridge. Since the base of the peduncles consists of descending pathways from the cerebral cortex, this part of the midbrain is the same phylogenetically new formation as the base of the pons or pyramid of the medulla oblongata.

Black substance

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Black substance separates the base and tegmentum of the cerebral peduncles. Its cells contain the pigment melanin. This pigment exists only in humans and appears at the age of 3–4 years. The substantia nigra receives impulses from the cerebral cortex, striatum and cerebellum and transmits them to the neurons of the superior colliculus and brainstem nuclei, and then to the motor neurons of the spinal cord. The substantia nigra plays an essential role in the integration of all movements and in the regulation of the plastic tone of the muscular system. Disruption of the structure and function of these cells causes parkinsonism.

Leg cover

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Leg cover continues the tegmentum of the pons and medulla oblongata and consists of phylogenetically ancient structures. Its upper surface serves as the bottom of the brain's aqueduct. The kernels are located in the tire bloc(IV) and oculomotor(III) nerves. These nuclei develop in embryogenesis from the main plate lying under the marginal sulcus, consist of motor neurons and are homologous to the anterior horns of the spinal cord. Lateral to the aqueduct, it extends along the entire midbrain nucleus of the mesencephalic tract trigeminal nerve. It receives proprioceptive sensitivity from the muscles of mastication and the muscles of the eyeball.

Medial longitudinal fasciculus

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Underneath the gray matter surrounding the aqueduct, from neurons intermediate core the phylogenetically old path begins - medial longitudinal fasciculus. It contains fibers connecting the nuclei of the oculomotor, trochlear and abducens nerves. The bundle is also joined by fibers starting from the nucleus of the vestibular nerve (VIII) and carrying impulses to the nuclei of the III, IV, VI and XI cranial nerves, as well as descending ones to the motor neurons of the spinal cord. The bundle passes into the pons and medulla oblongata, where it lies under the bottom of the fourth ventricle near the midline, and then into the anterior column of the spinal cord. Thanks to such connections, when the balance apparatus is irritated, the eyes, head and limbs move.

Red core

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In the region of the nuclei of the third pair of nerves lies the parasympathetic nucleus; it develops at the site of the border sulcus and consists of interneurons of the autonomic nervous system. In the upper part of the tegmentum of the midbrain there passes the dorsal longitudinal fasciculus, connecting the thalamus and hypothalamus with the nuclei of the brain stem.

At the level of the inferior colliculus it occurs cross fibers of the superior cerebellar peduncles. Most of them end up in massive cellular clusters lying in front - red nuclei (nucleus ruber), and the smaller part passes through the red nucleus and continues to the thalamus, forming dentate-thalamic tract.

Fibers from the cerebral hemispheres also end in the red nucleus. From its neurons there are ascending pathways, in particular to the thalamus. The main descending pathway of the red nuclei is rubrospinal (rednuclear-spinal cord). Its fibers, immediately upon exiting the nucleus, cross over and are directed along the tegmentum of the brain stem and the lateral cord of the spinal cord to the motor neurons of the anterior horns of the spinal cord. In lower mammals, this pathway transmits to them, and then to the muscles of the body, impulses switched in the red nucleus, mainly from the cerebellum. In higher mammals, the red nuclei function under the control of the cerebral cortex. They are an important part of the extrapyramidal system, which regulates muscle tone and has an inhibitory effect on the structures of the medulla oblongata.

The red nucleus consists of large cell and small cell parts. The large cell part is developed to a large extent in lower mammals, while the small cell part is developed in higher mammals and in humans. The progressive development of the small cell part proceeds in parallel with the development of the forebrain. This part of the nucleus is like an intermediate node between the cerebellum and the forebrain. The large cell part in humans is gradually reduced.

Lateral to the red nucleus in the tegmentum is located medial loop. Between it and the gray matter surrounding the aqueduct lie nerve cells and fibers reticular formation(continuation of the reticular formation of the pons and medulla oblongata) and pass through ascending and descending pathways.

Midbrain Development

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The midbrain develops in the process of evolution under the influence of visual afferentation. In lower vertebrates, which have almost no cerebral cortex, the midbrain is highly developed. It reaches significant sizes and, together with the basal ganglia, serves as a higher integrative center. However, only the superior colliculus is developed in it.

In mammals, in connection with the development of hearing, in addition to the upper ones, the lower tubercles also develop. In higher mammals and, in particular, in humans, in connection with the development of the cerebral cortex, the higher centers of visual and auditory functions move into the cortex. In this case, the corresponding centers of the midbrain find themselves in a subordinate position.

• Vestibular system
• Medial longitudinal fasciculus

Normally, eye movements are always simultaneous and combined. For the association of movements of the eyeballs, it is necessary not only to preserve the morphology and functions of the nuclear apparatus of the cranial nerves involved in ensuring such movements, the roots, trunks of these nerves and the eye muscles. The integrity of the associative connections between the cell groups (nuclei) included in the oculomotor apparatus and their adequate interaction with the vestibular system are also required. This requires preservation of the function of the medial longitudinal fasciculi and associated structures of the reticular formation, subcortical and cortical oculomotor centers.

Vestibular system, coordinating the work of the oculomotor system, actively participates in ensuring 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 damaged, vestibular reflexes are inhibited. Irritation of the vestibular structures can cause excessive involuntary eye movements such as nystagmus, tonic muscle reactions, coordination disorders, dizziness, and autonomic reactions.

Vestibular system

Vestibule of the labyrinth (labyrinthine vestibule) - part of the inner ear - connects the semicircular canals and the cochlea. Three semicircular bone canals belonging to the vestibular system are located in three mutually perpendicular planes and are interconnected. These canals, 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 the 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 otolithic apparatus of the inner ear. All three semicircular ducts end in ampoules containing receptor hair cells that make up the ampullar ridges. These scallops are embedded in a gelatinous substance that forms a dome over them. Receptor hair cells of the scallops are sensitive to the movement of 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.

The receptors of the otolith 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 gelatinous tissue containing sodium carbonate crystals - otoliths, a change in the position of which causes irritation of the receptor cells, and nerve impulses arise in them, signaling the position of the head in space.

From the peripheral apparatus of the vestibular system, impulses follow along 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. The bodies of the first neurons of the vestibular impulse pathway are located in it. From here, vestibular impulses follow along the axons of the same nerve cells that make up the vestibular portion of the VIII cranial nerve (n. vestibulocochlearis). The VIII nerve leaves the temporal bone through the internal auditory canal, crosses the lateral pontine cistern and enters the brainstem in the lateral part of the groove delimiting the basal surfaces of the pons and medulla oblongata.

Entering the brain stem, vestibular portion of the VIII nerve is 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 the ankylosing spondylitis 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 inferior nucleus of Roller (nucleus inferior).

The vestibular nuclei contain the bodies of the second neurons of the vestibular analyzer, the axons of which then follow in various directions, ensuring the formation of numerous vestibular connections. A significant part of the axons of nerve cells of the superior, lateral, medial and inferior vestibular nuclei take direct or indirect participation in the formation of the vestibular longitudinal fasciculus. They are directed upward, partially moving to the opposite side and ending at the cells of the nuclei of the III, IV and VI nerves, which provide innervation to the external ocular muscles of both eyes.

The presence of vestibulo-oculomotor connections creates the possibility of synchronizing the tension of the striated ocular agonist muscles and at the same time reducing the tension of the antagonist muscles, which is necessary to maintain the concordance of the movements of the eyeballs and gaze with changes in body position. The axons of the vestibular cells, taking a descending direction, participate 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 fasciculus

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

The medial (or posterior) longitudinal fasciculus (fasciculis longitudinalis medialis) is a paired formation, complex in composition and function, located in the covering of the brain stem, near the midline, under the cerebral aqueduct and the bottom of the rhomboid fossa of the fourth ventricle. The medial longitudinal fasciculus plays an important role in ensuring 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 brainstem and the diencephalon, the medial longitudinal fasciculus descends as part of the tegmentum of the trunk to the cervical spinal cord.

In this case, part of the fibers coming from the Darkshevich nucleus enters the medial longitudinal fasciculus of the same side, and part of it first passes through the posterior commissure of the brain to the other side, after which it is included in the medial longitudinal fasciculus of the opposite side. The medial longitudinal bundles from here pass through the tegmentum of the brain stem along its entire length, after which they penetrate 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 pier and constituting the nuclear apparatus of the spinal portion of the accessory (XI) cranial nerves.

The medial longitudinal fasciculi 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 cranial nuclei of the first (III, IV and VI), providing eye movements, the vestibular nuclei and adjacent sections of the reticular formation, as well as motor neurons of the anterior horns of the cervical spinal cord and accessory (XI) nerves.

Normally, excitation of any of the eye muscles is never isolated. 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 combined movements of both eyes. So, when you turn your gaze 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.

At the same time and necessarily in accordance with Sherrington’s law of reciprocal innervation, muscles that are antagonistic to contracting muscles relax.
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 fasciculus, innervating the external eye muscles and, thus, taking one or another part in the implementation of gaze movements. 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 influence the state of the oculomotor system.

Thus, the medial longitudinal fascicles form the anatomical basis of combined contractions and relaxations of the eye muscles and the resulting synchronous, simultaneous movements of both eyes. Largely thanks to the medial longitudinal fasciculi, normal movements of the eyeballs always occur simultaneously, in combination, in a friendly manner. Any change in the direction of gaze when tracking a moving object is manifested by simultaneous synchronous movements of the eyes (the phenomenon of eye conjugation), 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 in the composition of the medial longitudinal fasciculus, an important place is occupied by the axons of the vestibular nuclei (mainly the superior nucleus of Bechterew, the medial nucleus of Schwalbe and the lateral nucleus of Deiters), which make a partial decussation and are involved in the formation of bilateral connections, providing labyrinthine reflexes. These reflexes play a leading role in ensuring a certain direction of gaze and its fixation on an object when changing body position, especially when changing the position of the head.

Movements of the head lead to the generation of impulses in the receptor structures of the vestibular apparatus (in the membranous labyrinth, in the otolithic apparatus) that are transmitted to the vestibular nuclei. Synchronously with the change in muscle tone, aimed at holding the head in a given position, through the medial longitudinal fasciculus, 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 move in the opposite direction. In the case of rapid movement of an object, the gaze fixed on it will periodically move abruptly in the opposite direction. After this, the eyes continue to track the object. The combined eye movements that occur in such cases are manifestations of optokinetic nystagmus.

It is assumed that there are associative connections between the structures of the medial longitudinal fasciculus and the trigeminal nerve, ensuring 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 gaze fixed on a moving object through the fibers of the medial longitudinal fascicles.

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

Thus, the medial fascicle includes the axons of 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 nerve cells of the Darkshevich nucleus and the intermediate nucleus of Kohal. In addition, the medial fasciculus has connections with the nuclei of the colliculi, trigeminal nerve and reticular formation, as well as with the subcortical gaze centers, superior olive, cerebellum and 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 fasciculi, have bilateral connections with various parts of the central nervous system. Thus, the reticular system influences the functional state of the vestibulo-oculomotor connections and, by 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 disturbances in the functional state of the oculomotor system in the form of the appearance of ocular ataxia, pathological nystagmus, and difficulties in ensuring the gaze fixes a moving object.
The nuclei of the oculomotor nerves, through the 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 ensuring eimetry, correcting active movements by extinguishing inertia, as well as providing the most rational regulation of the tone of the reciprocal muscles.

All brain structures that send nerve signals directly or indirectly to the medial longitudinal fasciculus directly or indirectly affect the functions of the nuclei of the 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 colliculi quadrigemina, other subcortical oculomotor centers are usually considered supranuclear. The implementation of gaze reactions, which can be influenced by other supranuclear influences: optical, vestibular, acoustic, proprioceptive, tactile and painful stimuli, depends on the impulses emanating from them.

Thus, gaze movements depend on the state of many nerve structures, primarily on those that participate in the formation of the medial longitudinal fasciculus. Association of eye movements is possible only if the medial longitudinal fasciculus and the formations of the nervous system that form it are intact. Damage to the medial longitudinal fasciculus leads to various oculomotor disorders, the nature of which depends on the location and extent of the pathological process. Various forms of disorder of combined eye movements (gaze), pathological forms of nystagmus, ophthalmoparesis or ophthalmoplegia are possible.

In the dorsolateral parts of the medulla oblongata, fibers of the so-called spinal tract of the trigeminal nerve, tr. spinalis nervi trigemini. It is formed by processes of cells of the trigeminal (Gasserian) ganglion and is a conductor of impulses of tactile, pain, temperature and proprioceptive sensitivity on the face. The fibers that make up this tract end in the spinal nucleus of the trigeminal nerve, n. spinalis n. trigemini.

Posterior longitudinal fasciculus, fasciculus longitudinalis dorsalis, (Schütz's bundle) is a visceral coordinating system and is a bundle of longitudinally oriented fibers that runs along the bottom of the rhomboid fossa and connects the hypothalamic nuclei, the superior and inferior salivary nuclei, the double nucleus, and the posterior vagus nucleus into a single functioning chain nerve, solitary nucleus, motor nuclei of the facial and hypoglossal nerves.

Medial longitudinal fasciculus, fasciculus longitudinalis medialis, as well as the previous bundle, is an important coordinating system, in the formation of which the intermediate nucleus of Cajal, Darkshevich’s nucleus, motor nuclei of III, IV, VI pairs, nuclei of the vestibulocochlear and accessory nerves and motor neurons of the spinal cord innervating muscles take part neck. Thanks to the presence of these vertical projections, the work of the muscles of the neck and eyeballs is coordinated when turning the head. In addition, there are suggestions that the function of the medial longitudinal fasciculus is also to conduct impulses that coordinate the work of the muscles involved in the acts of swallowing, chewing, and voice formation.

Dorsal tegmental tract, tractus tegmentalis dorsalis, belongs to the extrapyramidal system. It originates in the red nuclei and central gray matter of the midbrain, caudate nucleus, putamen (belong to the basal nuclei of the cerebrum) and goes down, ending in the main olivary and double nuclei.

Mainly motor pathways.

The motor fibers of the medulla oblongata are represented mainly by the descending transit tracts of the pyramidal system, which originate from the Betz giant pyramidal cells in the motor zone of the cerebral cortex (precentral gyrus). The pyramidal tracts lie in the pyramids, are responsible for the implementation of voluntary motor acts and include two systems of descending pathways: corticospinal and corticonuclear.

Corticospinal tracts,tr. corticospinales, connect the upper two-thirds of the precentral gyrus with motor neurons of the anterior columns of the spinal cord and conduct impulses that provide voluntary movements of the trunk and limbs.

Fibers included in the composition corticonuclear tracts, tr. corticonucleares, connect the lower third of the precentral gyrus with the motor nuclei of the glossopharyngeal, vagus, accessory and hypoglossal nerves and are conductors of impulses that provide voluntary movements of the organs of the head and neck.

tectospinal tract,tr. tectospinalis, located between the medial lemniscus ventrally and the medial longitudinal fasciculus dorsally. Contains transit fibers descending from the subcortical centers of vision and hearing (midbrain quadrigeminal) to the motor neurons of the spinal cord. In a single connection with this tract there are projections of the so-called tegmental-bulbar tract,tr. tectobulbaris, which connects the quadrigeminal tract with the motor nuclei of the glossopharyngeal, vagus, accessory and hypoglossal nerves. These tracts belong to the extrapyramidal system and are the conducting link of reflex arcs responsible for the implementation of protective and orienting reflexes to visual and auditory stimuli.

Red nuclear spinal tract,tr. rubrospinalis, (Monakov's bundle) originates from the red nuclei, passes through the medulla oblongata in transit somewhat posterior to the Govers' bundle and ends in the motor neurons of the anterior columns of the spinal cord of the contralateral side. The functional purpose of this pathway is to redistribute muscle tone necessary to maintain balance without effort of will.

11.1. MIDDLE BRAIN

Midbrain (mesencephalon) can be seen as an extension of the bridge and upper headsail. It is 1.5 cm long and consists of the cerebral peduncles (pedunculi cerebri) and roofs (tectum mesencephali), or quadrigeminal plates. The conventional boundary between the roof and the underlying tegmentum of the midbrain passes at the level of the cerebral aqueduct (aqueduct of Sylvius), which is the cavity of the midbrain and connects the third and fourth ventricles of the brain.

The cerebral peduncles are clearly visible on the ventral side of the trunk. They are two thick cords that emerge from the substance of the bridge and, gradually diverging to the sides, enter the cerebral hemispheres. In the place where the cerebral peduncles depart from each other, between them there is an interpeduncular fossa (fossa interpeduncularis), closed by the so-called posterior perforated substance (substance perforata posterior).

The base of the midbrain is formed by the ventral sections of the cerebral peduncles. Unlike the base of the bridge, there are no transversely located nerve fibers and cell clusters. The base of the midbrain consists only of longitudinal efferent pathways running from the cerebral hemispheres through the midbrain to the lower parts of the brainstem and to the spinal cord. Only a small part of them, which is part of the cortical-nuclear pathway, ends in the tegmentum of the midbrain, in the nuclei of the III and IV cranial nerves located here.

The fibers that make up the base of the midbrain are arranged in a certain order. The middle part (3/5) of the base of each cerebral peduncle consists of pyramidal and corticonuclear pathways; medial to them are the fibers of the frontopontine tract of Arnold; laterally - fibers going to the pontine nuclei from the parietal, temporal and occipital lobes of the cerebral hemispheres - the Turk's path.

Above these bundles of efferent pathways are the structures of the midbrain tegmentum, containing the nuclei of the IV and III cranial nerves, paired formations related to the extrapyramidal system (substantia nigra and red nuclei), as well as structures of the reticular formation, fragments of the medial longitudinal bundles, as well as numerous conductive paths of different directions.

Between the tegmentum and the roof of the midbrain there is a narrow cavity, which has a sagittal orientation and provides communication between the III and IV cerebral ventricles, called the cerebral aqueduct.

The midbrain has its “own” roof - the quadrigeminal plate (lamina quadrigemini), which consists of two lower and two upper hillocks. The posterior colliculi belong to the auditory system, the anterior colliculi to the visual system.

Let us consider the composition of two transverse sections of the midbrain, made at the level of the anterior and posterior colliculi.

Section at the level of the posterior colliculus. At the border between the base and the tegmentum of the midbrain, in its caudal sections, there is a medial (sensitive) loop, which soon, rising upward, diverges to the sides, giving way to the medial parts of the anterior sections of the tegmentum red kernels (nucleus ruber), and the border with the base of the midbrain - substantia nigra (substance nigra). The lateral loop, consisting of conductors of the auditory pathway, in the caudal part of the tegmentum of the midbrain is displaced medially and part of it ends in the posterior tubercles of the quadrigeminal plate.

The substantia nigra has the shape of a strip - wide in the middle part, tapering at the edges. It consists of cells rich in the pigment myelin and myelin fibers, in the loops of which, as in the globus pallidus, rare large cells are located. The substantia nigra has connections with the hypothalamic region of the brain, as well as with formations of the extrapyramidal system, including the striatum (nigrostriatal tracts), the subthalamic Lewis nucleus and the red nucleus.

Above the substantia nigra and medially from the medial lemniscus there are cerebellar-red nuclear tracts that penetrate here as part of the upper cerebellar peduncles (decussatio peduncularum cerebellarum superiorum), which, passing to the opposite side of the brain stem (Wernecking's decussation), end at the cells of the red nuclei.

Above the cerebellar-red nuclear tract is the reticular formation of the midbrain. Between the reticular formation and the central gray matter lining the aqueduct, medial longitudinal fascicles pass. These bundles begin at the level of the metathalamic part of the diencephalon, where they have connections with the nuclei of Darkshevich and the intermediate nuclei of Cajal located here. Each of the medial bundles passes along its side through the entire brain stem close to the midline under the aqueduct and the bottom of the fourth ventricle of the brain. These bundles anastomose with each other and have numerous connections with the nuclei of the cranial nerves, in particular with the nuclei of the oculomotor, trochlear and abducens nerves, which ensure synchronization of eye movements, as well as with the vestibular and parasympathetic nuclei of the trunk, with the reticular formation. The tectospinal tract passes near the posterior longitudinal fasciculus (tractus tectospinalis), starting from the cells of the anterior and posterior colliculi of the quadrigeminal. Upon leaving them, the fibers of this pathway bend around the gray matter surrounding the aqueduct and form the cross of Meynert (decussatio tractus tigmenti), after which the tectospinal tract descends through the underlying parts of the trunk into the spinal cord, where they end in its anterior horns at the peripheral motor neurons. Above the medial longitudinal fasciculus, partly as if pressed into it, is the nucleus of the fourth cranial nerve (nucleus trochlearis), innervating the superior oblique muscle of the eye.

The posterior colliculus of the quadrigeminal is the center of complex unconditioned auditory reflexes; they are interconnected by commissural fibers. Each of them contains four cores, consisting of different sizes

Rice. 11.1.Section of the midbrain at the level of the cerebral peduncles and the anterior tuberculum. 1 - nucleus of the III (oculomotor) nerve; 2 - medial loop; 3 - occipital-temporal-pontine tract; 4 - substantia nigra; 5 - corticospinal (pyramidal) tract; 6 - frontal-pontine tract; 7 - red core; 8 - medial longitudinal fasciculus.

and cell shape. From the fibers of the part of the lateral loop included here, capsules are formed around these nuclei.

Cut at the level of the anterior colliculus (Fig. 11.1). At this level, the base of the midbrain appears wider than in the previous section. The decussation of the cerebellar pathways has already completed, and the red nuclei dominate on both sides of the median suture in the central part of the tegmentum (nuclei rubri), in which the efferent pathways of the cerebellum passing through the superior cerebellar peduncle (cerebellar-red nuclear pathways) mainly end. Fibers coming from the globus pallidus are also suitable here. (fibre pallidorubralis), from the thalamus (tractus thalamorubralis) and from the cerebral cortex, mainly from their frontal lobes (tractus frontorubralis). The red nucleus-spinal tract of Monakov originates from large cells of the red nucleus (tractus rubrospinalis), which, upon leaving the red core, immediately passes to the other side, forming a cross (dicussatio fasciculi rubrospinalis) or Trout Cross. The red nucleus spinal tract descends as part of the tegmentum of the brain stem to the spinal cord and participates in the formation of its lateral cords; it ends in the anterior horns of the spinal cord at the peripheral motor neurons. In addition, bundles of fibers extend from the red nucleus to the inferior olive of the medulla oblongata, to the thalamus, and to the cerebral cortex.

In the central gray matter, under the bottom of the aqueduct, there are caudal sections of the nuclei of Darkshevich and the intermediate nuclei of Cajal, from which the medial longitudinal fasciculi begin. The fibers of the posterior commissure, related to the diencephalon, also originate from the Darkshevich nuclei. Above the medial longitudinal fasciculus, at the level of the superior colliculus, in the tegmentum of the midbrain are located the nuclei of the third cranial nerve. As on

In the previous section, on the section made through the superior colliculus, the same descending and ascending pathways pass through, which occupy a similar position here.

The anterior (upper) colliculi of the quadrigeminal have a complex structure. They consist of seven alternating fibrous cell layers. There are commissural connections between them. They are also connected to other parts of the brain. Some of the fibers of the optic tract end there. The anterior colliculi are involved in the formation of unconditioned visual and pupillary reflexes. Fibers also depart from them and are included in the tegnospinal tracts belonging to the extrapyramidal system.

11.2. CRANIAL NERVES OF THE MIDDLEBRAIN

11.2.1. Trochlear (IV) nerve (n. trochlearis)

Trochlear nerve (n. trochlearis, IV cranial nerve) is motor. It innervates only one striated muscle, the superior oblique muscle of the eye. (m. obliquus superior), turning the eyeball down and slightly outward. Its nucleus is located in the tegmentum of the midbrain at the level of the posterior colliculus. The axons of the cells located in this nucleus constitute the nerve roots, which pass through the central gray matter of the midbrain and the anterior medullary velum, where, unlike other cranial nerves of the brainstem, they make a partial decussation, after which they emerge from the upper surface of the brainstem near the frenulum of the forebrain. sail. Having circled the lateral surface of the cerebral peduncle, the trochlear nerve passes to the base of the skull; here it enters the outer wall of the cavernous sinus, and then through the superior orbital fissure it penetrates into the orbital cavity and reaches the eye muscle innervated by it. Since the IV cranial nerve in the anterior medullary velum makes a partial decussation, alternating syndromes involving this nerve do not occur. Unilateral damage to the trunk of the IV cranial nerve leads to paralysis or paresis of the superior oblique muscle of the eye, manifested by strabismus and diplopia, especially significant when turning the gaze downward and inward, for example, when descending stairs. When the IV cranial nerve is damaged, a slight tilt of the head in the direction opposite to the affected eye is also characteristic (compensatory posture due to diplopia).

11.2.2. Oculomotor (III) nerve (n. oculomotorius)

oculomotor nerve, n. oculomotorius(III cranial nerve) is mixed. It consists of motor and autonomic (parasympathetic) structures. In the tegmentum of the midbrain at the level of the superior colliculus there is a group of heterogeneous nuclei (Fig. 11.2). The motor paired magnocellular nuclei, which provide innervation to most of the external striated muscles of the eye, occupy a lateral position. They consist of cell groups, each of which is related to the innervation of a specific muscle. In the anterior part of these nuclei there is a group of cells, the axons of which provide innervation to the muscle that lifts the upper eyelid

Rice. 11.2.Location of the nuclei of the oculomotor (III) nerve [According to L.O. Darkshevich]. 1 - core for the muscle that lifts the upper eyelid (m. levator palpebrae); 2 - core for the superior rectus muscle (m. rectus superior); 3 - core for the inferior rectus muscle (m. rectus inferior); 4 - core for the inferior oblique muscle (m. obliquus inferior); 5 - nucleus for the medial rectus muscle of the eye (m. rectus medialis); 6 - nucleus for the muscle that constricts the pupil (m. sphincter pupillae, Yakubovich-Edinger-Westphal kernel); 7 - accommodation nucleus (Perlia nucleus).

(m. levator palpebrae superioris), followed by cell groups for the muscles that rotate the eyeball upward (m. rectus superior), up and out (m. obliquus inferior), inside (m. rectus medialis) and down (m. rectus inferior).

Medial to the paired large cell nuclei are the paired small cell parasympathetic nuclei of Yakubovich-Edinger-Westphal. Impulses coming from here pass through the ciliary vegetative node (ganglion ciliare) and reach two smooth muscles - the internal muscles of the eye - the muscle that constricts the pupil and the ciliary muscle (m. sphincter pupillae et m. ciliaris). The first of them provides constriction of the pupil, the second - accommodation of the lens. On the midline between the Yakubovich-Edinger-Westphal nuclei there is an unpaired nucleus of Perlia, which, apparently, is related to the convergence of the eyeballs.

Damage to individual cell groups belonging to the system of nuclei of the third cranial nerve leads to disruption of only those functions that they directly influence. In this regard, when the tegmentum of the midbrain is damaged, the dysfunction of the third cranial nerve may be partial.

The axons of the cells of the nuclei of the oculomotor nerve go down, while those that begin from the cells located in the caudal cell groups of the lateral magnocellular nucleus partially pass to the other side. The root of the third cranial nerve thus formed crosses the red nucleus and leaves the midbrain, emerging at the base of the skull from the medial groove of the cerebral peduncle at the edge of the posterior perforated substance. Subsequently, the trunk of the III cranial nerve is directed forward and outward and enters the upper, and then moves into the outer wall of the cavernous sinus, where it is located next to the IV and VI cranial nerves and the first branch of the V cranial nerve. Coming out of the sinus wall, the III nerve, again together with the IV and VI nerves and the first branch of the V nerve, enters the orbital cavity through the superior orbital fissure, where it divides into branches going to the indicated external striated muscles of the eye, and the parasympathetic portion of the III nerve ends in the ciliary ganglion, from which they extend to the internal smooth muscles of the eye (m. sphincter pupillae et m. ciliaris) parasympathetic postganglionic fibers. If damage to the nuclear apparatus of the third cranial nerve can manifest itself as a selective disorder of the functions of individual muscles innervated by it, then pathological changes in the trunk of this nerve usually lead to a disorder of the functions of all muscles that it innervates

Rice. 11.3.Muscles that provide movement of the eyeballs and their innervation (III, IV, VI cranial nerves). Directions of displacement of the eyeballs during contraction of these muscles. R. ext. - external rectus muscle (it is innervated by the VI cranial nerve); O. inf. - inferior oblique muscle (III nerve); R. sup. - superior rectus muscle (III nerve); R. med. - medial rectus muscle (III nerve); R. inf. - inferior rectus muscle (III nerve); O. sup. (III nerve) - superior oblique muscle (IV nerve).

must provide. Concomitant neurological disorders depend on the level of damage to the third cranial nerve and on the nature of the pathological process (Fig. 11.3).

Damage to the oculomotor nerve can cause drooping (ptosis) of the upper eyelid and divergent strabismus, which occurs due to the predominant influence on the position of the eyeball of the rectus externus muscle of the eye, innervated by the sixth cranial nerve (Fig. 11.4). Double vision (diplopia) occurs, and movements of the eyeball in all directions except outer are absent or severely limited. No convergence

Rice. 11.4.Damage to the right oculomotor (III) nerve:

a - ptosis of the upper eyelid; b - divergent strabismus and anisocoria, revealed by passive elevation of the upper eyelid.

eyeball (normally observed when an object moving in the sagittal plane approaches the bridge of the nose). Due to paralysis of the muscle that constricts the pupil, it becomes dilated and does not respond to light, while both the direct and conjugate reaction of the pupil to light is disrupted (see Chapters 13, 30).

11.3. MEDIAL LONGITUDINAL FASCILUS AND SIGNS OF ITS DAMAGE

Medial (posterior) longitudinal fasciculus (fasciculis longitudinalis medialis)- a paired formation, complex in composition and function, starting from the Darkshevich nucleus and the intermediate nucleus of Cajal at the level of the metathalamus. The medial longitudinal fasciculus passes through the entire brain stem near the midline, ventral to the central periaqueductal gray matter, and under the bottom of the fourth ventricle of the brain penetrates the anterior cords of the spinal cord, ending at the cells of its anterior horns at the cervical level. It is a collection of nerve fibers belonging to various systems. It consists of descending and ascending pathways that connect paired cellular formations of the brain stem, in particular the III, IV and VI nuclei of the cranial nerves, innervating the muscles that provide eye movements, as well as the vestibular nuclei and cellular structures that are part of the reticular formation, and anterior horns of the cervical spinal cord.

Due to the associative function of the medial longitudinal fasciculus, normal movements of the eyeballs are always friendly and combined. Involvement of the medial longitudinal fasciculus in the pathological process leads to the occurrence of various oculovestibular disorders, the nature of which depends on the location and extent of the pathological focus. Damage to the medial longitudinal fasciculus can cause various forms of gaze disturbance, strabismus and nystagmus. Damage to the medial fasciculus most often occurs with severe traumatic brain injury, with impaired blood circulation in the brain stem, with its ea8 compression as a result of herniation of the structures of the mediobasal parts of the temporal lobe into Bichat's fissure (the gap between the edge of the notch of the tentorium of the cerebellum and the cerebellar peduncle), with compression of the brain stem tumor of subtentorial localization, etc. (Fig. 11.5).

When the medial longitudinal fasciculus is damaged, the following syndromes are possible.

Gaze paresis- a consequence of dysfunction of the medial fasciculus - the inability or limitation of a friendly rotation of the eyeballs in one direction or another horizontally or vertically.

To assess gaze mobility, the patient is asked to follow an object moving horizontally and vertically. Normally, when turning the eyeballs to the sides, the lateral and medial edges of the cornea should touch the outer and inner commissure of the eyelids, respectively, or approach them at a distance of no more than 1-2 mm. Rotation of the eyeballs is normally possible downward by 45?, upward - by 45-20? depending on the age of the patient.

Paresis of gaze in the vertical plane - usually results from damage to the midbrain tegmentum and metathalamus at the level of the posterior commissure of the brain and the part of the medial longitudinal fasciculus located at this level.

Rice. 11.5.Innervation of the eye muscles and medial longitudinal fasciculi, ensuring their connections with each other and with other brain structures.

1 - nucleus of the oculomotor nerve; 2 - accessory nucleus of the oculomotor nerve (Yakubovich-Edinger-Westphal nucleus); 3 - posterior central nucleus of the oculomotor nerve (Perlia's nucleus), 4 - ciliary ganglion; 5 - nucleus of the trochlear nerve; 6 - nucleus of the abducens nerve; 7 - proper nucleus of the medial longitudinal fasciculus (Darkshevich nucleus); 8 - medial longitudinal fascicle; 9 - adversive center of the premotor zone of the cerebral cortex; 10 - lateral vestibular nucleus.

Syndromes of damage to 1a and 1b - magnocellular nucleus of the oculomotor (III) nerve,

II - accessory nucleus of the oculomotor nerve; III - nuclei of the IV nerve; IV - nuclei of the VI nerve; V and VI - damage to the right adversive field or the left pontine gaze center. Paths that provide conjugal eye movements are indicated in red.

Paresis of gaze in the horizontal plane develops when the pontine tegmentum is damaged at the level of the nucleus of the VI cranial nerve, the so-called pontine center of gaze (paresis of gaze towards the pathological process).

Gaze paresis in the horizontal plane also occurs when the cortical gaze center, located in the posterior part of the middle frontal gyrus, is damaged. In this case, the eyeballs turn towards the pathological lesion (the patient “looks” at the lesion). Irritation of the cortical center of gaze may be accompanied by a combined rotation of the eyeballs in the direction opposite to the pathological focus (the patient “turns away” from the focus), as sometimes happens, for example, during an epileptic seizure.

Floating eye symptom lies in the fact that in comatose patients, in the absence of paresis of the ocular muscles, due to dysfunction of the medial fasciculi, the eyes spontaneously perform floating movements. They are slow in tempo, non-rhythmic, chaotic, can be either friendly or asynchronous, appear more often in the horizontal direction, but individual movements of the eyes in the vertical direction and diagonally are also possible. During floating movements of the eyeballs, the oculocephalic reflex is usually preserved. These eye movements are a consequence of gaze disorganization and cannot be reproduced voluntarily, always indicating the presence of severe organic brain pathology. With pronounced inhibition of brainstem functions, floating eye movements disappear.

Hertwig-Magendie sign - a special form of acquired strabismus, in which the eyeball on the affected side is turned downward and inward, and the other is turned upward and outward. This dissociated eye position persists even with changes in gaze position. The symptom is caused by damage to the medial longitudinal fasciculus in the tegmentum of the midbrain. More often it occurs as a result of circulatory disorders in the brain stem, and is possible with a tumor of subtentorial localization or traumatic brain injury. Described in 1826 by the German physiologist K.H. Hertwig (1798-1887) and in 1839 the French physiologist F. Magendie (1783-1855).

Internuclear ophthalmoplegia - a consequence of unilateral damage to the medial longitudinal fasciculus in the tegmentum of the brain stem in the area between the middle part of the pons and the nuclei of the oculomotor nerve and the resulting deefferentation of these nuclei. Leads to gaze disturbance (conjugate movements of the eyeballs) due to a disorder of the innervation of the ipsilateral internal (medial) rectus muscle of the eye. As a result, paralysis of this muscle occurs and the inability to rotate the eyeball in the medial direction beyond the midline or moderate (subclinical) paresis, leading to a decrease in the speed of adduction of the eye (to its adduction delay), while on the side opposite the affected medial longitudinal fasciculus, monocular abduction nystagmus. The convergence of the eyeballs is preserved. With unilateral internuclear ophthalmoplegia, divergence of the eyeballs in the vertical plane is possible; in such cases, the eye is located higher on the side of the lesion of the medial longitudinal fasciculus. Bilateral internuclear ophthalmoplegia is characterized by paresis of the muscle that adducts the eyeball on both sides, a violation of conjugate eye movements in the vertical plane and gaze turns when checking the oculocephalic reflex. Damage to the medial longitudinal fasciculus in the anterior part of the midbrain can also lead to a violation of the convergence of the eyeballs. Cause of internuclear

Ophthalmoplegia can be multiple sclerosis, circulatory disorders in the brain stem, metabolic intoxication (in particular, with paraneoplastic syndrome), etc.

Lutz syndrome- a variant of internuclear ophthalmoplegia, characterized by supranuclear abduction palsy, in which voluntary outward movements of the eye are impaired, but reflexively, with caloric stimulation of the vestibular apparatus, its complete abduction is possible. Described by the French doctor H. Lutz.

One and a half syndrome - a combination of pontine paresis of gaze in one direction and manifestations of internuclear ophthalmoplegia when looking in the other direction. The anatomical basis of one-and-a-half syndrome is a combined lesion of the ipsilateral medial longitudinal fasciculus and the pontine center of gaze or the pontine paramedian reticular formation. The clinical picture is based on impaired eye movements in the horizontal plane with intact vertical excursion and convergence. The only possible movement in the horizontal plane is the abduction of the eye opposite to the pathological focus with the occurrence of its mononuclear abduction nystagmus with complete immobility of the eye ipsilateral to the pathological focus. The name “one and a half” has the following origin: if the usual friendly movement in one direction is taken as 1 point, then gaze movements in both directions amount to 2 points. With one-and-a-half syndrome, the patient retains the ability to avert only one eye, which corresponds to 0.5 points from the normal range of eye movements in the horizontal plane. Consequently, 1.5 points are lost. Described in 1967 by the American neurologist C. Fisher.

Oculocephalic reflex (the “doll’s head and eyes” phenomenon, the “doll’s eyes” test, Cantelli’s symptom) - reflex deviation of the eyeballs in the opposite direction when turning the patient’s head in the horizontal and vertical planes, which is carried out by the examiner first slowly and then quickly (do not check if damage to the cervical spine is suspected!). After each rotation, the patient’s head should be held in the extreme position for some time. These gaze movements are carried out with the participation of brain stem mechanisms, and the sources of impulses going to them are the labyrinth, vestibular nuclei and cervical proprioceptors. In patients in a coma, the test is considered positive if, when tested, the eyes move in the direction opposite to the turn of the head, maintaining their position in relation to external objects. A negative test (lack of eye movements or incoordination) indicates damage to the pons or midbrain or barbiturate poisoning. Normally, reflex movements of the gaze when checking the oculocephalic reflex in a awake person are suppressed. When consciousness is preserved or slightly suppressed, the vestibular reflex, which causes the phenomenon, is completely or partially suppressed, and the integrity of the structures responsible for its development is checked by asking the patient to fix his gaze on a certain object, while passively turning his head. If the patient is in a drowsy state, in the process of testing the oculocephalic reflex, during the first two or three turns of the head, friendly turns of the gaze in the opposite direction appear, but then disappear, since the test leads to the awakening of the patient. Described the disease by Cantelli.

Convergent nystagmus. It is characterized by spontaneous slow convergent movements such as drift, interrupted by fast convergent shocks. Occurs when the tegmentum of the midbrain and its connections are damaged, and can alternate with retraction nystagmus. Described in 1979 by Ochs et al.

Vestibulo-ocular reflex - reflex coordinated movements of the eyeballs, ensuring that the point of fixation is maintained in the zone of best vision in cases of changes in the position of the head, as well as gravity and acceleration. They are carried out with the participation of the vestibular system and cranial nerves that innervate the muscles that provide gaze movements.

11.4. CENTRAL SYMPATHETIC PATHWAY

The central sympathetic pathway presumably begins in the nuclei of the posterior part of the hypothalamus and in the reticular formation of the anterior parts of the trunk. At the level of the midbrain and pons, it passes under the cerebral aqueduct and under the lateral parts of the floor of the fourth ventricle of the brain near the spinothalamic tract. The autonomic sympathetic fibers that make up the central sympathetic pathway end at the sympathetic cells of the lateral horns of the spinal cord, in particular at the cells of the ciliospinal sympathetic center. Damage to the central sympathetic pathway and this center located in the spinal cord segments C VIII - Th I is manifested primarily by Horner syndrome (Claude Bernard-Horner) (see Chapter 13).

11.5. SOME SYNDROMES OF DAMAGE TO THE MIDNBRAIN AND ITS CRANIAL NERVES

Quadrigeminal syndrome. When the midbrain is damaged on both sides, there is a violation of upward gaze rotation, combined with a weakening or absence of a direct and friendly reaction to light on both sides and with a violation of the convergence of the eyeballs.

When the pathological focus is localized in one half of the midbrain, the following syndromes may occur.

Knapp syndrome- dilation of the pupil (paralytic mydriasis) on the side of the pathological process in combination with central hemiparesis on the opposite side, manifests itself when the autonomic portion of the third cranial nerve or the parasympathetic nucleus of the midbrain is affected, as well as the pyramidal tract, in particular with the mediobasal herniation syndrome temporal lobe into Bichat's fissure (see Chapter 21). Refers to alternating syndromes. Described by the German ophthalmologist H.J. Knapp (1832-1911).

Weber syndrome (Weber-Hübler-Gendre syndrome) - alternating syndrome that occurs when the base of the cerebral peduncle is damaged in the area where it is crossed by the root of the oculomotor nerve. It manifests itself on the affected side as paresis or paralysis of the external and internal muscles of the eye (ptosis of the upper eyelid, ophthalmoparesis or ophthalmoplegia, mydriasis); on the opposite side, central hemiparesis is noted (Fig. 11.6). More often it occurs due to circulatory problems in the oral part of the brain stem. Opi-

Rice. 11.6.Schematic representation of the development of alternating syndromes of Weber (a) and Benedict (b).

1 - nuclei of the oculomotor nerve;

2 - medial longitudinal fasciculus;

3 - substantia nigra; 4 - occipital-temporo-parietal tract; 5, 6 - frontopontine tract; 7 - red nucleus, 8 - medial longitudinal fasciculus. Lesions are shaded.

The English doctor H. Weber (1823-1918) and the French doctors A. Gubler (1821-1879) and A. Gendrin (1796-1890) were born.

Benedict's syndrome - alternating syndrome when the pathological focus is localized in the tegmentum of the midbrain, at the level of the nuclei of the oculomotor nerve, the red nucleus and cerebellar-red nuclear connections. It manifests itself on the affected side as pupil dilation in combination with paralysis of the striated muscles innervated by the oculomotor nerve, and on the opposite side - intention tremor, sometimes hyperkinesis of the choreoathetosis type and hemihypesthesia. Described in 1889 by the Austrian neuropathologist M. Benedikt (1835-1920).

Superior red nucleus syndrome (Foix syndrome) occurs if the pathological focus is located in the tegmentum of the midbrain in the area of ​​​​the upper part of the red nucleus, and manifests itself on the opposite side as cerebellar hemitremor (intentional tremors), which can be combined with hemiataxia and choreoathetosis. The oculomotor nerves are not involved in the process. Described by the French neuropathologist Ch. Foix (1882-1927).

Inferior red nucleus syndrome (Claude syndrome) - alternating syndrome caused by damage to the lower part of the red nucleus, through which the root of the third cranial nerve passes. On the side of the pathological process there are signs of damage to the oculomotor nerve (ptosis of the upper eyelid, dilated pupil, divergent strabismus), and on the opposite side

on the side, cerebellar disorders (intentional tremors, hemiataxia, muscle hypotonia). Described in 1912 by the French neuropathologist N. Claude (1869-1946).

Nothnagel syndrome - a combination of signs of damage to the nuclear apparatus of the oculomotor nerve with hearing loss and cerebellar ataxia, which can be observed on both sides and at the same time be unevenly expressed. Occurs when there is damage or compression of the roof and tegmentum of the midbrain, as well as the superior cerebellar peduncles and structures of the metathalamus, primarily the internal geniculate bodies. More often it appears with tumors of the anterior parts of the trunk or pineal gland. Described in 1879 by the Austrian neuropathologist K. Nothnagel (1841-1905).

Cerebral aqueduct syndrome (Korber-Salus-Elschnig syndrome) - retraction and trembling of the eyelids, anisocoria, convergence spasm, vertical gaze paresis, nystagmus - a manifestation of damage to the gray matter surrounding the cerebral aqueduct, signs of occlusive hydrocephalus. Described by the German ophthalmologist R. Koerber and the Austrian ophthalmologists R. Salus (born in 1877) and A. Elschnig (1863-1939).

11.6. SYNDROMES OF DAMAGE TO THE BRAINSTEM AND CRANIAL NERVES AT DIFFERENT LEVELS

Oculofacial congenital paralysis (Mobius syndrome) - agnesia (aplasia) or atrophy of the motor nuclei, underdevelopment of the roots and trunks of III, VI, VII, less often - V, XI and XII cranial nerves, and sometimes the muscles innervated by them. It is characterized by lagophthalmos, manifestations of Bell's symptom, congenital, persistent, bilateral (less often unilateral) paralysis or paresis of the facial muscles, which is manifested, in particular, by difficulties in sucking, inexpressiveness or lack of facial reactions, drooping corners of the mouth from which saliva flows. In addition, various forms of strabismus, sagging of the lower jaw, atrophy and immobility of the tongue are possible, which leads to disruption of food intake, and subsequently articulation, etc. It can be combined with other developmental defects (microophthalmia, underdevelopment of the cochleovestibular system, hypoplasia of the lower jaw, aplasia of the pectoralis major muscle, syndactyly, clubfoot), mental retardation. There are both hereditary and sporadic cases. Etiology unknown. Described in 1888-1892. German neuropathologist P. Moebius (1853-1907).

Paralytic strabismus - strabismus, which occurs with acquired paralysis or paresis of the muscles that provide movement of the eyeballs (a consequence of damage to the system of III, IV or VI cranial nerves), is usually combined with double vision (diplopia).

Non-paralytic strabismus - congenital strabismus (squint). It is characterized by the absence of diplopia, since in such cases the perception of one of the images is compensatory suppressed. Reduced vision in the eye that does not capture the image is called amblyopia without anopia.

Synkinesis of the Hun (Marcus Hun) - a type of pathological synkinesis in some lesions of the brain stem accompanied by ptosis. Due to the preservation of embryonic connections between the motor nuclei of the trigeminal and oculomotor nerves, combined movements of the eyes and lower

lower jaw., characterized by involuntary raising of the drooping eyelid when opening the mouth or when chewing. Described by an English ophthalmologist

R.M. Gunn (1850-1909).

Superior orbital fissure syndrome (sphenoidal fissure syndrome) - combined dysfunction of the oculomotor, trochlear, abducens, and ophthalmic branches of the trigeminal nerves passing from the cavity of the middle cranial fossa into the orbit through the superior orbital (sphenoidal) fissure, characterized by ptosis of the upper eyelid, diplopia, ophthalmoparesis or ophthalmoplegia in combination with signs irritation (trigeminal pain) or decreased function (hypalgesia) of the optic nerve. Depending on the nature of the main process, there may be various accompanying manifestations: exophthalmos, hyperemia, swelling in the orbital area, etc. It is a possible sign of a tumor or inflammatory process in the area of ​​the medial part of the lesser wing of the main bone.

Orbital apex syndrome (Rolle syndrome) - a combination of signs of superior orbital fissure syndrome and damage to the optic nerve, as well as exophthalmos, vasomotor and trophic disorders in the orbital area. Described by the French neuropathologist J. Rollet (1824-1894).

Orbital floor syndrome (Dejean syndrome) - manifested by ophthalmoplegia, diplopia, exophthalmos and hyperpathy in combination with pain in the area innervated by the ophthalmic and maxillary branches of the trigeminal nerve. This syndrome, which appears during pathological processes in the area of ​​the bottom of the orbit, was described by the French ophthalmologist Ch. Dejan (born 1888).

Diabetic polyneuropathy of cranial nerves - acutely or subacutely developing asymmetrical reversible polyneuropathy of the cranial nerves (usually oculomotor, abducens, facial, trigeminal), sometimes occurring in patients with diabetes mellitus.

Koller's syndrome (Kolle) - ophthalmoplegia in combination with pain in the area innervated by the optic nerve (the first branch of the trigeminal nerve) with periostitis in the area of ​​the superior orbital fissure. It can develop after hypothermia and during the transition of the inflammatory process from the paranasal sinuses. It is characterized by relative short duration and reversibility. Described in 1921 by the American neuropathologist J. Collier (1870-1935).

Painful ophthalmoplegia syndrome (Tolosa-Hunt syndrome, steroid-sensitive ophthalmoplegia) - non-purulent inflammation (pachymeningitis) of the outer wall of the cavernous sinus, superior orbital fissure or apex of the orbit. The inflammatory process involves all or some of the cranial nerves that provide movement of the eyeballs (III, IV and VI nerves), the ophthalmic, less commonly, the maxillary branch of the trigeminal nerve and the sympathetic plexus of the internal carotid artery due to its periarteritis, and sometimes the optic nerve. It manifests itself as a sharp, constant “drilling” or “gnawing” pain in the orbital, retroorbital and frontal areas in combination with ophthalmoparesis or ophthalmoplegia; decreased vision, Horner’s syndrome, sometimes moderate exophthalmos, signs of venous stagnation in the fundus are possible. The syndrome of painful ophthalmoplegia persists for several days or several weeks, after which spontaneous remission usually occurs, sometimes with residual neurological deficits. After remission from several weeks to many years, there may be a relapse of painful ophthalmoplegia syndrome. There are no morphological changes outside the cavernous sinus zone, and there is no basis for diagnosing systemic pathology. The infectious-allergic nature of the process is recognized. Characteristic positive reaction

for treatment with corticosteroids. Currently considered as an autoimmune disease with clinical and morphological polymorphism, it is characterized by the manifestation of benign granulomatosis in the structures of the base of the skull. Similar clinical manifestations are possible with aneurysm of the vessels of the base of the skull, parasellar tumor, and basal meningitis. Described in 1954 by the French neuropathologist F.J. Tolosa (1865-1947) and in more detail - in 1961, the American neurologist W.E. Hunt (1874-1937) et al.

Lateral wall of the cavernous sinus syndrome (Foix's syndrome) - paresis of the external rectus muscle, and then other external and internal muscles of the eye on the side of the pathological process, which leads to ophthalmoparesis or ophthalmoplegia and disorder of pupillary reactions, while exophthalmos and severe swelling of the tissues of the eyeball due to venous stagnation are possible. The causes of the syndrome may be thrombosis of the cavernous sinus, the development of a carotid artery aneurysm in it. Described in 1922 by the French doctor Ch. Foix (1882-1927).

Jefferson syndrome - aneurysm of the internal carotid artery in the anterior part of the cavernous sinus, manifested by pulsating noise in the head in combination with signs characteristic of cavernous sinus syndrome. Characterized by pain and swelling of the tissues of the fronto-orbital region, chymosis, ophthalmoplegia, mydriasis, pulsating exophthalmos, hypalgesia in the area of ​​the optic nerve. In advanced cases, expansion and deformation of the superior orbital fissure and atrophy of the anterior sphenoid process, detected on craniograms, are possible. The diagnosis is clarified by carotid angiography data. Described in 1937 by the English neurosurgeon G. Jefferson.

Superior orbital fissure syndrome (sphenoidal fissure syndrome, retrosphenoidal space syndrome, Jaco-Negri syndrome) - a combination of signs of damage to the optic, oculomotor, trochlear, trigeminal and abducens nerves on one side. It is observed with tumors of the nasopharynx growing into the middle cranial fossa and cavernous sinus, manifested by the Jacquot triad. It was described by the modern French physician M. Jacod and the Italian pathologist A. Negri (1876-1912).

Triad Jaco.On the affected side, blindness, ophthalmoplegia are noted and, due to the involvement of the trigeminal nerve in the process, intense constant, sometimes intensifying pain in the area innervated by it, as well as peripheral paresis of the masticatory muscles. Occurs with retrosphenoidal space syndrome. Described by the modern French physician M. Jacco.

Glicky's syndrome- alternating syndrome associated with damage to several levels of the brain stem. It is characterized by combined damage to the II, V, VII, X cranial nerves and the corticospinal tract. It manifests itself on the side of the pathological process as decreased vision or blindness, peripheral paresis of facial muscles, pain in the supraorbital region and difficulty swallowing, on the opposite side - spastic hemiparesis. Described by domestic doctor V.G. Glicks (1847-1887).

Garcin's syndrome (hemicranial polyneuropathy) - damage to all or almost all cranial nerves on one side without signs of damage to the brain substance, changes in the composition of the cerebrospinal fluid and manifestations of intracranial hypertension syndrome. It usually occurs in connection with an extradural malignant neoplasm of craniobasal localization. More often it is a sarcoma of the base of the skull, originating from the nasopharynx, sphenoid bone or pyramid of the temporal bone. Characterized by destruction of the bones of the base of the skull. Described in 1927 by the French physician R. Garsin (1875-1971).

Bundle system (fasciculi proprii)

Bundle system (fasciculi proprii). The main bundles of the spinal cord consist of short ascending and descending fibers that arise and terminate 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, immediately surrounding the gray matter. Some fibers of the fasciculi proprii ventralis, lying on the sides of the anterior longitudinal fissure and designated as fasciculus sulco-marginalis, directly continue into the brainstem, where they are called fasciculus longitudinalis medialis or fasc. longitudinalis posterior. The main bundles 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 in the development and evolution of the vertebrate nervous system. 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 fascicle. The medial longitudinal fasciculus is a bundle of motor coordination fibers running along the entire length of the brain stem and is closely linked to the vestibular apparatus.

Fasc. longitudinalis medialis consists mainly of thick fibers that become covered with myelin at a very early stage of development, approximately at the same time as 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 large in amphibians and reptiles. Due to its early myelination and in contrast with the thin, more or less scattered fibers of the tectospinal tract located in front of it, this bundle protrudes especially sharply in the stem part of the brain of the uterine baby.

Like a clearly defined 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 fasciculus 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 fasciculus.

Downwards fasc. longitudinalis medialis can be traced to the decussation 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 medulla; depends on the fact that immediately anterior to these pathways in the medulla oblongata there is a decussation of the medial lemniscus, and even more anterior to the decussion of the pyramidal tracts.

Upper fasc. longitudinalis medialis is located 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 ocular 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 sulcus. 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 the nerve cells of the lateral vestibular Ara (Deiters nucleus). The axons of these cells, passing through the adjacent areas of the reticular formation, enter the longitudinal medial fascicle of the same or opposite side and are divided 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, force the eyeball to respond appropriately to proprioceptive impulses arising in the semicircular canals. The descending branches, in turn, establish connections 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, can 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 the trigeminal nerve, and 3) from the cells of the interstitial nucleus of Cajal and Darshkevich's nucleus.