Medial longitudinal fasciculus and its role. Medial longitudinal fasciculus and signs of its damage
Latin name: fasciculus longitudinalis medialis.
Where is it located?
In the brainstem, the MPP is located close to the central line, ventral to the central gray matter, passing slightly anterior to the oculomotor nerve nuclei. In the thickness of the brain stem, the medial longitudinal fasciculus can be found in any section of the longitudinal section. The MPP originates from the rostral interstitial nucleus of the longitudinal fasciculus (riMPP). Going down a little lower, bundles from the Darkshevich and Cajal nucleus join the fibers from the riMPP. Thus, the tip of the medial longitudinal fasciculus resembles a flower bouquet.
Anatomy
Let us remember that when talking about a separate structure in the brain, we should not forget that the human brain has two hemispheres, two hemispheres. This means that the structure we are describing is also a pair structure. Often, the pairing of brain structures means that the exchange of data between them is carried out due to crossovers, jumpers (anastomoses), and special fibers. However, there are exceptions. Among them is the medial longitudinal fasciculus.
MPP is formed by a group of fibers pressed tightly against each other. The proximity of the fibers of one side to the opposite side allows you to avoid switching, jumpers, and individual fibers and freely exchange signals.
What function?
The main role of the MPP is participation in oculomotor functions. The fibers of the Medial longitudinal fasciculus are associated with the nuclei, which provide a wide variety of movements of the eyeball. Signals flow into the MPP mainly from oculomotor innervation, as well as vestibular and auditory ones. Due to this special structure, a number of the most important functions of the body are carried out. Fibers from some cranial nuclei enter the medial longitudinal fasciculus to coordinate the response of innervated structures.
| Midbrain nuclei | Bridge Cores | Nuclei of the medulla oblongata |
|---|---|---|
| Rostral interstitial nuclei of the medial longitudinal fasciculus | Abducens nerve nuclei | Giant cell reticular nucleus |
| Darkshevich kernels | Vestibular nuclei | Vestibular nuclei |
| Cajal nuclei | Auditory nuclei |
|
| Yakubovich-Edinger-Westphal kernels | Pontine reticular nucleus |
|
| Perlia Core |
|
|
| Proprietary nuclei of the oculomotor nerve |
|
|
| Trochlear nerve nuclei |
|
|
| Prepository kernels |
|
|
And how does it work?
A personal command comes from each core and, merging into the MPP, the command is distributed to all fibers connected to the system. To give an example, an MPP can be compared to a section of a highway. By gathering into a single stream, any signal can turn in the direction it needs.
Pathology
Knowing what functions are provided by the structures whose fibers are part of the MPP, we can assume disorders when this structure is damaged.
Most often, these are various manifestations of oculomotor functions: gaze paresis (impossibility of simultaneously looking in any direction), strabismus, symptom of floating eyes (disconnected movements). All these symptoms are characteristic of the so-called internuclear ophthalmoplegia.
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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 the 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 leaving 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.
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 appearance in higher animals and humans of the cortical end of the auditory and visual analyzers, the auditory and visual centers of the midbrain fell into a subordinate position. At the same time, they became intermediate, subcortical.
With the development of the forebrain in higher mammals and humans, 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, arranged 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 to 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 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 muscles.
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 colliculi. 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.
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 nuclei of the hypothalamus, the superior and inferior salivary nuclei, the double nucleus, the posterior nucleus of the vagus 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.
