Medial longitudinal fasciculus. Medial longitudinal fasciculus and signs of its damage

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 VI cranial nerve (Fig. 11.4). Double vision (diplopia) occurs; 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 (Moebius 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.

Midbrain (mesencephalon)(Fig. 4.4.1, 4.1.24) develops during 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 were also formed here, which, together with the vision centers, later grew in the form of four mounds of the roof of the midbrain. With the advent of the cortical end of the auditory and visual analyzers in higher animals and humans, 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, pathways began to pass through the midbrain, connecting the telencephalon cortex with the spinal cord

through the cerebral peduncles. As a result, the human midbrain contains:

1. Subcortical centers of vision and nerve nuclei
ovs that innervate the muscles of the eye.

2. Subcortical auditory centers.

3. All ascending and descending conductions
pathways connecting the cerebral cortex
with the spinal cord.

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

Accordingly, the midbrain has two main parts: the roof of the midbrain (tectum mesencephalicum), where the subcortical centers of hearing and vision, and the cerebral peduncles are located (cms cerebri), where the conductive pathways predominantly pass.

1. The roof of the midbrain (Fig. 4.1.24) is hidden under the posterior end of the corpus callosum and is divided by two criss-crossing grooves - longitudinal and transverse - into four colliculi, 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 - sensory root of the trigeminal nerve; 3 - basal groove of the bridge; 4 - vestibulocochlear nerve; 5 - facial nerve; 6 - ventrolateral sulcus of the medulla oblongata; 7 - olive; 8 - circummolyvar bundle; 9 - pyramid of the medulla oblongata; 10 - anterior median fissure; // - cross of pyramidal fibers); b - rear view (/ - pineal gland; 2 - superior tubercles of the quadrigeminal; 3 - lower tubercles of the quadrigeminal; 4 - rhomboid fossa; 5 - knee of the facial nerve; 6 - median fissure of the rhomboid fossa; 7 - superior cerebellar peduncle; 8 - middle cerebellar peduncle; 9 - inferior cerebellar peduncle; 10 - vestibular region; //-triangle of the hypoglossal nerve; 12 - triangle of the vagus nerve; 13 - tubercle of the wedge-shaped fasciculus; 14 - tubercle of tender core; /5 - median sulcus)

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

2. Brain peduncles (pedunculi cerebri) contain
all pathways to the forebrain.
The cerebral peduncles look like two thick halves
lindrical white cords 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
tatcom of the primary cavity of the midbrain
bubble, looks like a narrow channel and is called
brain plumbing (aqueductus cerebri). He
represents a narrow, ependyma-lined ca
cash 1.5-2.0 cm length connecting III and IV
ventricles. Restrict the water supply dorsally
is formed by the roof of the midbrain, and ventrally -
covering of the cerebral peduncles.

In a cross section of the midbrain, three main parts are distinguished:

1. Roof plate (lamina tecti).

2. Tire (tegmentum), representing
upper part of the cerebral peduncles.

3. Ventral cerebral peduncle, or os
cerebral peduncle aching (basis pedunculi cerebri).
According to the development of the midbrain under
the influence of the visual receptor is embedded in it
we have various nuclei related to in
nervation of the eye (Fig. 4.1.25).

The cerebral aqueduct is surrounded by central gray matter, which in its function is related to the autonomic system. In it, under the ventral wall of the aqueduct, in the tegmentum of the cerebral peduncle, the nuclei of two motor cranial nerves are located - 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, corresponding to the innervation of several muscles of the eyeball. A small, also paired, vegetative accessory nucleus is located medially and posteriorly to it. (nucleus accessorius) and the 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 cerebral peduncle is the nucleus of the medial longitudinal fasciculus.

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

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

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

Between the base of the cerebral peduncle (basis pedunculi cerebralis) and a tire (tegmentum) the substantia nigra is located (substantia nigra). The pigment melanin is found in the cytoplasm of the neurons of this substance.

From the tegmentum of the midbrain (tegmentum mesencephali) the central tire path departs (tractus tegmentalis centralis). It is a projection descending tract, which contains fibers coming from the optic thalamus, globus pallidus, red nucleus, as well as the reticular formation of the midbrain in the direction of the reticular formation and the 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 ventral to the substantia nigra, the base of the cerebral peduncle contains longitudinal nerve fibers descending from the cerebral cortex to all underlying parts of the central nervous system. (tractus corticopontinus, corticonuclearis, cortico-spinalis and etc.). The tegmentum, located dorsal to the substantia nigra, contains predominantly

Anatomy of the brain

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

Among the gray matter nuclei, the most significant nucleus is the red nucleus (nucleus ruber). This elongated formation extends in the tegmentum of the cerebral peduncle from the hypothalamus of the diencephalon to the inferior colliculus, where an important descending pathway begins from it (tractus rubrospinalis), connecting the red nucleus to the anterior horns of the spinal cord. The bundle of nerve fibers, after leaving the red nucleus, intersects with a similar bundle of fibers on the opposite side in the ventral part of the median suture - the ventral decussation of the tegmentum. The red nucleus is a very important coordination center 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 nucleus-spinal tract extending from it, influence the entire striated muscle.

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

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

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

The medial longitudinal fasciculus 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 fasciculus has extensive connections with the floculonodular lobe of the cerebellum (lobus flocculonodularis), which ensures coordination of 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 fasciculus

facial, vestibulocochlear nerves).

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

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

Ascending fibers arise 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 fasciculus to the trochlear and dorsal oculomotor nucleus on the same side (motor neurons 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 part of the nuclei of the oculomotor complex.

The interconnections of the medial longitudinal fasciculus are the axons of interneurons 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 to the abducens nerve nucleus.

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

Chapter 4. BRAIN AND EYE

Formation switches fibers from the supranuclear structures to the cerebral cortex.

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

Superior tubercles (mounds) of the quadrigeminal(collicius superior)(Fig. 4.1.24-4.1.27).

The superior colliculi 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. A transverse groove separates the superior colliculi from the inferior colliculi. Above the superior colliculus is the visual hillock. The great cerebral vein lies above the midline.

The superior colliculi of the quadrigeminal have a multilayered cellular structure (see “Visual Pathway”). 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 quadrigeminal region is largely sensory. It is projected onto the external geniculate body and the pillow.

Pillow of the optic thalamus

Pretectal region

Rice. 4.1.27. Schematic representation of the main connections of the superior colliculi

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

The superficial layers of the quadrigeminal process process visual information and, together with the deep layers, provide orientation of the head and eyes in the process of identifying new visual stimuli.

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

Superficial cells respond to stationary and moving visual stimuli. Deep cells typically fire before a saccade.

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

reproducing a saccade, the direction of which is directed towards the visual target. The superficial and deep layers can function independently.

The inferior colliculi are part of the auditory pathway.

The tegmentum of the midbrain is located anterior or ventral to the colliculus. The aqueduct of Sylvius runs longitudinally between the roof and the tegmentum of the midbrain. The midbrain tegmentum contains numerous descending and ascending fibers related to the somatosensory and motor systems. In addition, the tire contains several nuclear groups, including nuclei III and IV pairs of cranial nerves, the red nucleus, as well as a cluster of neurons belonging to the reticular formation. The tegmentum of the midbrain is considered as a central accumulation of motor and reticular fibers that go from the diencephalon to the medulla oblongata.

Ventral or anterior to the midbrain tegmentum there is a large paired bundle of fibers - the cerebral peduncle, 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 there 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 that promote vertical gaze, vergence movements of the eye, and eye accommodation. Neurons in 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 synapses for the pupillary reflex. Some of the abducens fibers intersect in the area of gray matter located around the aqueduct of Sylvius. The fibers are directed to the parvocellular nuclei of the oculomotor nerve, which control the pupillomotor fibers.

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

Anatomy of the brain

New longitudinal beam. The lateral spinothalamic tract carries afferent pain fibers and is located in the tegmentum of the midbrain on the outside. The medial lemniscus transmits sensory and tactile information, as well as information about body position. It is located medially in the pons but moves laterally in the midbrain. It is a continuation of the medial loops. The lemniscus connects the thin and cuneate nuclei with the nuclei of the optic thalamus.

Longitudinal medial fascicle (f. longitudinalis medialis, PNA, BNA, JNA) P. nerve fibers, starting from the intermediate nucleus and the central gray matter of the midbrain (Darkshevich’s nucleus), passing near the midline through the brain stem and ending in the cervical segments of the spinal cord; also contains fibers connecting the nuclei of the VIII pair with the nuclei of the III, IV and VI pairs of cranial nerves.

Large medical dictionary. 2000 .

See what a “longitudinal medial bundle” is in other dictionaries:

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There are no isolated movements of one eyeball. Eye movements are always simultaneous and combined, which requires the joint movement of several external eye muscles, innervated by different nerves. In Fig. Figure 37 shows that, for example, when looking up, four muscles innervated from the four cell groups of the nuclei of the third nerve contract simultaneously; when looking down - two muscles innervated by the III nerves and two - from the IV nerves; when looking to the side, a simultaneous contraction of m occurs. recti externi (VI nerve) of one and m. recti interni (III nerve) of the other eye; with the convergence of the ocular axes, both mm are reduced. recti interni from nuclei nn. oculomotorium; finally, a number of other combined muscle contractions occur with “oblique” directions of gaze, for example, to the right and up, etc. If we also take into account that when any oculomotor muscles contract, the tone of the corresponding antagonist muscles must simultaneously decrease, then the need for a very subtle and precise innervation system regulating eye movements becomes clear.
Both reflex and voluntary movements of the eyeballs are always associated and combined. All this is due to the presence of a special connecting innervation system, which provides both internuclear (III, IV, VI nerves of both sides) connections, and connections between the nuclei of the eye muscles and other parts of the nervous system. Such a system is the posterior longitudinal fasciculus (fasciculus longitudinalis posterior, or medialis). The bundle nuclei or Darkshevich nuclei are located anterior to the nn nuclei. oculomotorii, near the habenula and comissura posterior.
The fibers of both bundles are directed down the brain stem, located in the bottom of the Sylvian aqueduct and the rhomboid fossa dorsally, on the sides and close to the midline and give collaterals to the cells of the nuclei of the III, IV and VI pairs of nerves, which ensures the compatibility and simultaneity of movements of the eye muscles in that or some other combination.
Other fibers that make up the posterior longitudinal fascicle are fibers from the cells of the vestibular nucleus, directed into the fascicle on both its own and the opposite side. They branch into ascending and descending branches: those heading upward contact the cells of the nuclei of the eye muscles; descending - descend into the spinal cord, pass through it as part of the anterior columns and end near the cells of the anterior horns - tractus vestibulo-spinalis.
“Variable” innervation of gaze is carried out from the so-called “center” of voluntary rotation of the eyes and head in the opposite direction, located in the posterior part of the second frontal gyrus. Fibers from the cortex, approaching the pons in its anterior section, intersect and end near the nucleus n. abducentis of the opposite side, therefore. From the nucleus of the VI nerve, the impulse simultaneously spreads along the nerve to m. rectus externus and to the cell group of the III nerve, giving fibers to m. rectus internus of the other eye, which causes a combined rotation of the eyeballs towards this nucleus (“pontine center of gaze”), but in the opposite hemisphere where the impulse originated. Consequently, when the second frontal gyrus is damaged, gaze paralysis in the opposite direction is observed, and when the pons is damaged, it is distal to the intersection of the central fibers in it or the nucleus n. abducentis, gaze paralysis is observed in the direction where the lesion is located. In both cases, due to the predominance of unaffected antagonists, a combined deviation of the eyeballs and head may occur when the bridge is affected - in the direction opposite to the focus; in case of damage to the cortical parts - towards the lesion. When the posterior part of the second frontal gyrus is irritated (Jacksonian epilepsy), tonoclonic convulsions of the eye muscles and head are observed in the direction opposite to the source of irritation.

Posterior longitudinal beam system.
1 - nucleus of the posterior longitudinal fasciculus (Darkshevich nucleus); 2 and 5 - posterior longitudinal fascicle; 3 - vestibular nerve; 4 - vestibulo-spinal bundle.

The localization of the cortical projection (pathways) of turning the eyes up and down is not well understood; Apparently, it is located close to the projection of turning to the side, at the base of the same second frontal gyrus. Fibers from here enter the system of the posterior longitudinal fasciculus through the nuclei n. oculomotorii. Processes in the area of the anterior colliculus - nuclear (III nerves) and perinuclear - are often accompanied by upward and downward gaze paralysis, similar to how lesions in the pons or in the region of the nuclei of the VI nerves cause sideways gaze paralysis.

Table 11

Group of nerves of the eye muscles

Nuclei, their localization	Exit from the brain	Exit from the skull
In the bottom of the Sylvian aqueduct, at the level of the anterior colliculus	At the border of the cerebral peduncles and the pons, on the medial side of the cerebral peduncles
In the bottom of the Sylvian aqueduct, at the level of the posterior tuberosities of the quadrigeminal	From the dorsal surface of the brain, behind the quadrigeminal, crossing in the anterior medullary velum	Via fissura orbitalis superior
In the bottom of the rhomboid fossa, in the colliculus facialis (in the bridge)	At the border of the pons and medulla oblongata, at the level of the pyramids	Via fissura orbitalis superior

When the posterior longitudinal fasciculus is damaged, nystagmus is also observed.
The connections just discussed determine the innervation of gaze from the cerebral cortex. Through the vestibular nucleus, the posterior longitudinal fasciculus establishes connections with the vestibular apparatus and the cerebellum. Connections with the extrapyramidal system appear to occur through the Darkshevich nuclei. The descending fibers of the posterior longitudinal fasciculus provide connections with the spinal cord. Finally, there are connections between the nuclei of the ocular muscles and the subcortical centers of vision and hearing (anterior and posterior colliculi), which causes an “involuntary” reflexive turn of the eyes and head towards visual or auditory stimulation.