Anatomy of the extrinsic muscles of the eye. Muscular apparatus of the eye Muscles of the orbit of the eye

Oculomotor apparatus- a complex sensorimotor mechanism, the physiological significance of which is determined by its two main functions: motor (motor) and sensory (sensitive).

The motor function of the oculomotor system ensures the guidance of both eyes, their visual axes and the central fossae of the retinas to the object of fixation; the sensory function ensures the merging of two monocular (right and left) images into a single visual image.

The innervation of the extraocular muscles by the cranial nerves determines the close connection between neurological and ocular pathologies, as a result of which an integrated approach to diagnosis is necessary.

The constant stimulus for adduction (to ensure orthophoria) caused by the divergence of the orbits explains the fact that the medial rectus muscle is the most powerful of the rectus extraocular muscles. The disappearance of the stimulus for convergence with the onset of amaurosis leads to a noticeable deviation of the blind eye towards the temple.

All rectus muscles and the superior oblique begin in the depths of the orbit on the common tendon ring (anulus tendineus communis), fixed to the sphenoid bone and periosteum around the optic canal and partially at the edges of the superior orbital fissure. This ring surrounds the optic nerve and ophthalmic artery. The muscle that lifts the upper eyelid (m. levator palpebrae superioris) also begins from the common tendon ring. It is located in the orbit above the superior rectus muscle of the eyeball, and ends in the thickness of the upper eyelid. The rectus muscles are directed along the corresponding walls of the orbit, on the sides of the optic nerve, forming a muscular funnel, pierce the vagina of the eyeball (vagina bulbi) and with short tendons are woven into the sclera in front of the equator, 5-8 mm away from the edge of the cornea. The rectus muscles rotate the eyeball around two mutually perpendicular axes: vertical and horizontal (transverse).

Movements of the eyeball are carried out with the help of six extraocular muscles: four straight - external and internal (m. rectus externum, m.rectus internum), upper and lower (m.rectus superior, m.rectus inferior) and two obliques - upper and lower ( m.obliguus superior, m.obliguus inferior).

Superior oblique muscle of the eye originates from the tendon ring between the superior and internal rectus muscles and goes anteriorly to the cartilaginous block located in the superior internal corner of the orbit at its edge. At the pulley, the muscle turns into a tendon and, passing through the pulley, turns posteriorly and outward. Located under the superior rectus muscle, it is attached to the sclera outward from the vertical meridian of the eye. Two-thirds of the entire length of the superior oblique muscle is between the apex of the orbit and the trochlea, and one-third is between the trochlea and its attachment to the eyeball. This part of the superior oblique muscle determines the direction of movement of the eyeball during its contraction.

Unlike the five muscles mentioned inferior oblique muscle of the eye begins at the lower inner edge of the orbit (in the area of ​​the entrance of the nasolacrimal canal), goes posteriorly outward between the orbital wall and the inferior rectus muscle towards the external rectus muscle and is fan-shaped attached under it to the sclera in the posteroexternal part of the eyeball, at the level of the horizontal meridian of the eye.

Numerous cords extend from the fascial membrane of the extraocular muscles and Tenon’s capsule to the orbital walls.

The fascial-muscular apparatus ensures a fixed position of the eyeball and gives smoothness to its movements.

Some elements of the anatomy of the extrinsic muscles of the eye

All these nerves pass into the orbit through the superior orbital fissure.

The oculomotor nerve, after entering the orbit, divides into two branches. The superior branch innervates the superior rectus muscle and the levator palpebrae superioris, the inferior branch innervates the internal and inferior rectus muscles, as well as the inferior oblique.

The nucleus of the oculomotor nerve and the nucleus of the trochlear nerve located behind it and next to it (provides the work of the oblique muscles) are located at the bottom of the aqueduct of Sylvius (aqueduct of the brain). The nucleus of the abducens nerve (provides the work of the external rectus muscle) is located in the pons under the bottom of the rhomboid fossa.

The rectus oculomotor muscles of the eye are attached to the sclera at a distance of 5-7 mm from the limbus, the oblique muscles - at a distance of 16-19 mm.

The width of the tendons at the muscle attachment site ranges from 6-7 to 8-10 mm. Of the rectus muscles, the widest tendon is the internal rectus muscle, which plays a major role in the function of bringing together the visual axes (convergence).

The line of attachment of the tendons of the internal and external muscles of the eye, i.e., their muscular plane, coincides with the plane of the horizontal meridian of the eye and is concentric with the limbus. This causes horizontal movements of the eyes, their adduction, rotation to the nose - adduction during contraction of the internal rectus muscle and abduction, rotation towards the temple - abduction during contraction of the external rectus muscle. Thus, these muscles are antagonistic in nature.

The superior and inferior rectus and oblique muscles of the eye perform mainly vertical movements of the eye. The line of attachment of the superior and inferior rectus muscles is located somewhat obliquely, their temporal end is further from the limbus than the nasal end. As a result, the muscular plane of these muscles does not coincide with the plane of the vertical meridian of the eye and forms an angle with it that is on average 20° and open to the temple.

This attachment ensures rotation of the eyeball under the action of these muscles, not only upward (during contraction of the superior rectus muscle) or downward (during contraction of the inferior rectus muscle), but simultaneously inwardly, i.e. adduction.

The oblique muscles form an angle of about 60° with the plane of the vertical meridian, open to the nose. This determines the complex mechanism of their action: the superior oblique muscle lowers the eye and produces its abduction (abduction), the inferior oblique muscle is an elevator and also an abductor.

In addition to horizontal and vertical movements, these four vertically acting oculomotor muscles of the eye perform torsional eye movements clockwise or counterclockwise. In this case, the upper end of the vertical meridian of the eye deviates towards the nose (intrusion) or towards the temple (extortion).

Thus, the extraocular muscles of the eye provide the following eye movements:

• adduction (adduction), i.e. its movement towards the nose; this function is performed by the internal rectus muscle, additionally by the superior and inferior rectus muscles; they are called adductors;
• abduction (abduction), i.e. movement of the eye towards the temple; this function is performed by the external rectus muscle, additionally by the superior and inferior oblique muscles; they are called abductors;
• upward movement - under the action of the superior rectus and inferior oblique muscles; they are called lifters;
• downward movement - under the action of the inferior rectus and superior oblique muscles; they are called lowerers.

The complex interactions of the extraocular muscles of the eye are manifested in the fact that when moving in some directions they act as synergists (for example, partial adductors - the superior and inferior rectus muscles, in others - as antagonists (superior rectus - levator, inferior rectus - depressor).

The extraocular muscles provide two types of conjugal movements of both eyes:

• unilateral movements (in the same direction - right, left, up, down) - so-called version movements;
• opposite movements (in different directions) - vergence, for example, to the nose - convergence (bringing together the visual axes) or to the temple - divergence (spreading the visual axes), when one eye turns to the right, the other to the left.

Vergence and version movements can also be performed in the vertical and oblique directions.

The functions of the oculomotor muscles described above characterize the motor activity of the oculomotor apparatus, while the sensory one is manifested in the function of binocular vision.

Schematic representation of the movement of the eyeballs during contraction of the corresponding muscles:

Oculomotor apparatus- a complex sensorimotor mechanism, the physiological significance of which is determined by its two main functions: motor (motor) and sensory (sensitive).

The motor function of the oculomotor system ensures the guidance of both eyes, their visual axes and the central fossae of the retinas to the object of fixation; the sensory function ensures the merging of two monocular (right and left) images into a single visual image.

The innervation of the extraocular muscles by the cranial nerves determines the close connection between neurological and ocular pathologies, as a result of which an integrated approach to diagnosis is necessary.

18.1. Anatomical and physiological features

Movements of the eyeball are carried out with the help of six extraocular muscles: four straight - external and internal (i.e. rectus externum, m.rectus internum), upper and lower (m.rectus superior, m.rectus inferior) and two obliques - upper and lower ( m.obliguus superior, m.obliguus inferior).

All rectus and superior oblique muscles begin at the tendon ring, located around the optic nerve canal at the apex of the orbit and fused with its periosteum (Fig. 18.1). The rectus muscles in the form of ribbons are directed anteriorly parallel to the corresponding walls of the orbit, forming the so-called muscular funnel. At the equator of the eye, they pierce Tenon’s capsule (the vagina of the eyeball) and, before reaching the limbus, they are woven into the superficial layers of the sclera. Tenon's capsule supplies the muscles with a fascial covering that is missing in the proximal region where the muscles begin.

The superior oblique muscle originates at the tendon ring between the superior and internal rectus muscles and goes anteriorly to the cartilaginous block located in the upper inner corner of the orbit at its edge. At the pulley, the muscle turns into a tendon and, passing through the pulley, turns posteriorly and outward. Located under the superior rectus muscle, it is attached to the sclera outward from the vertical meridian of the eye. Two-thirds of the entire length of the superior oblique muscle is between the apex of the orbit and the trochlea, and one-third is between the trochlea and its attachment to the eyeball. This part of the superior oblique muscle determines the direction of movement of the eyeball during its contraction.

In contrast to the five muscles mentioned, the inferior oblique muscle begins at the inferior internal edge of the orbit (in the area of ​​the entrance of the nasolacrimal canal), goes posteriorly outward between the orbital wall and the inferior rectus muscle towards the external rectus muscle and is fan-shaped attached under it to the sclera in the posterolateral part of the eye apple, at the level of the horizontal meridian of the eye.

Numerous cords extend from the fascial membrane of the extraocular muscles and Tenon’s capsule to the orbital walls.

The fascial-muscular apparatus ensures a fixed position of the eyeball and gives smoothness to its movements.

The muscles of the eye are innervated by three cranial nerves:

• oculomotor nerve - n. axis-lomotorius (III pair) - innervates the internal, superior and inferior rectus muscles, as well as the inferior oblique;
• trochlear nerve - n. trochlearis (IV pair) - superior oblique muscle;
• abducens nerve - n. abducens (VI pair) - external rectus muscle.

All these nerves pass into the orbit through the superior orbital fissure.

The oculomotor nerve, after entering the orbit, divides into two branches. The superior branch innervates the superior rectus muscle and the levator palpebrae superioris, the inferior branch innervates the internal and inferior rectus muscles, as well as the inferior oblique.

The nucleus of the oculomotor nerve and the nucleus of the trochlear nerve located behind it and next to it (provides the work of the oblique muscles) are located at the bottom of the aqueduct of Sylvius (aqueduct of the brain). The nucleus of the abducens nerve (provides the work of the external rectus muscle) is located in the pons under the bottom of the rhomboid fossa.

The rectus oculomotor muscles are attached to the sclera at a distance of 5-7 mm from the limbus, the oblique muscles - at a distance of 16-19 mm.

The width of the tendons at the muscle attachment site ranges from 6-7 to 8-10 mm. Of the rectus muscles, the widest tendon is the internal rectus muscle, which plays a major role in the function of bringing together the visual axes (convergence).

The line of attachment of the tendons of the internal and external muscles, i.e., their muscular plane, coincides with the plane of the horizontal meridian of the eye and is concentric with the limbus. This causes horizontal movements of the eyes, their adduction, rotation to the nose - adduction during contraction of the internal rectus muscle and abduction, rotation towards the temple - abduction during contraction of the external rectus muscle. Thus, these muscles are antagonistic in nature.

The superior and inferior rectus and oblique muscles perform mainly vertical movements of the eye. The line of attachment of the superior and inferior rectus muscles is located somewhat obliquely, their temporal end is further from the limbus than the nasal end. As a result, the muscular plane of these muscles does not coincide with the plane of the vertical meridian of the eye and forms an angle with it that is on average 20° and open to the temple.

This attachment ensures rotation of the eyeball under the action of these muscles, not only upward (during contraction of the superior rectus muscle) or downward (during contraction of the inferior rectus muscle), but simultaneously inwardly, i.e. adduction.

The oblique muscles form an angle of about 60° with the plane of the vertical meridian, open to the nose. This determines the complex mechanism of their action: the superior oblique muscle lowers the eye and produces its abduction (abduction), the inferior oblique muscle is an elevator and also an abductor.

In addition to horizontal and vertical movements, these four vertically acting oculomotor muscles perform torsional eye movements clockwise or counterclockwise. In this case, the upper end of the vertical meridian of the eye deviates towards the nose (intrusion) or towards the temple (extortion).

Thus, the extraocular muscles provide the following eye movements:

• adduction (adduction), i.e. its movement towards the nose; this function is performed by the internal rectus muscle, additionally by the superior inferior rectus muscle; they are called adductors;
• abduction (abduction), i.e. movement of the eye towards the temple; this function is performed by the external rectus muscle, additionally by the superior and inferior oblique muscles; they are called abductors;
• upward movement - under the action of the superior rectus and inferior oblique muscles; they are called lifters;
• downward movement - under the action of the inferior rectus and superior oblique muscles; they are called lowerers.

The complex interactions of the oculomotor muscles are manifested in the fact that when moving in some directions they act as synergists (for example, partial adductors - the superior and inferior rectus muscles, in others - as antagonists (superior rectus - levator, inferior rectus - depressor).

The extraocular muscles provide two types of conjugal movements of both eyes:

• unilateral movements (in the same direction - right, left, up, down) - so-called version movements;
• opposite movements (in different directions) - vergence, for example, to the nose - convergence (bringing together the visual axes) or to the temple - divergence (spreading the visual axes), when one eye turns to the right, the other to the left.

Vergence and version movements can also be performed in the vertical and oblique directions.

The functions of the oculomotor muscles described above characterize the motor activity of the oculomotor apparatus, while the sensory one is manifested in the function of binocular vision.

Binocular vision, i.e. vision with two eyes, when an object is perceived as a single image, is possible only with clear conjugal movements of the eyeballs. The eye muscles ensure that the two eyes are positioned on the object of fixation so that its image falls on identical points in the retinas of both eyes. Only in this case does a single perception of the object of fixation occur. Identical, or corresponding, are the central foveae and points of the retina, located at the same distance from the central fovea in the same meridian. The points of the retina, located at different distances from the central fovea, are called disparate, inappropriate (non-identical). They do not have the innate property of single perception. When the image of the object of fixation hits non-identical points of the retina, double vision or diplopia occurs (Greek diplos - double, opos - eye), a very painful condition. This occurs, for example, with strabismus, when one of the visual axes is shifted to one side or the other from the common point of fixation.

The two eyes are located in the same frontal plane at a certain distance from each other, so in each of them not quite identical images of objects located in front and behind the object of fixation are formed. As a result, double vision inevitably occurs, called physiological. It is neutralized in the central section of the visual analyzer, but serves as a conditioned signal for the perception of the third spatial dimension, i.e. depth.

Such a displacement of images of objects (closer and further away from the points of fixation) to the right and left of the macula on the retinas of both eyes creates the so-called transverse disparation (displacement) of the images and their entry (projection) onto disparate areas (non-identical points), which causes double vision, including physiological.

Transverse disparity- the primary factor of deep perception. There are secondary, auxiliary factors that help in assessing the third spatial dimension. This is linear perspective, the size of objects, the location of light and shadow, which helps the perception of depth, especially in the presence of one eye, when transverse disparity is excluded.

The concept of binocular vision is associated with terms such as fusion (the psychophysiological act of merging monocular images), fusion reserves that provide binocular fusion at a certain degree of convergence (convergence) and separation (divergence) of the visual axes.

There are only six oculomotor muscles, four of them are straight, two are oblique. The muscles received this name due to the peculiarities of their course in the orbit, as well as their attachment to the apple of the eye. The work of muscles is controlled by three cranial nerves: oculomotor, abducens, trochlear. Each muscle fiber of this muscle group is rich in nerve endings, which provides movements with particular precision and clarity.

Thanks to the oculomotor muscles, variability of movements of the eyeballs is ensured, including unidirectional ones - up, to the right, etc., and multidirectional ones - bringing the eyes together. The essence of such movements is that, due to coordinated muscular work, the same image of an object falls on one area of ​​the retina - the macular area, which ensures good vision and gives a sense of spatial depth.

It is customary to distinguish six oculomotor muscles, four of them go in a forward direction and are called rectus muscles: internal, external, superior, inferior. The remaining two have a slightly oblique direction of movement, as well as a way of attaching the eye to the apple, and therefore are called oblique: upper and lower.

All muscles, excluding the inferior oblique, originate in a dense connective tissue ring that surrounds the external opening in the optic canal. At the very beginning, 5 muscles form a kind of muscular funnel, where the optic nerve, blood vessels and nerves pass. Afterwards, the superior oblique muscle gradually deviates upward and inward, moving towards the so-called block. This is the place where the muscle transforms into a tendon, thrown through the pulley loop, which is why it changes direction to oblique, then attaching in the area of ​​the upper outer quadrant of the eyeball below the superior rectus muscle. The inferior oblique muscle originates from the inferior internal orbital margin, passes below the inferior rectus muscle outward and posteriorly, and is attached in the region of the inferior external quadrant of the eyeball.

In the immediate vicinity of the eyeball, a superficial layer appears on the muscles - a dense capsule of Tenon's membrane. Their attachment to the sclera occurs at different distances from the limbus. The internal rectus muscle is attached especially close to the limbus of the rectus muscles, and the superior rectus muscle is further away from the rest. The oblique muscles are attached to the apple of the eye slightly behind the equator of the eyeball - the middle of its length.

The work of muscles is largely regulated by the oculomotor nerve. It controls the internal, superior, inferior oblique and inferior rectus muscles. The functions of the external rectus muscle are controlled by the abducens nerve, while the superior oblique muscle is controlled by the trochlear nerve. The peculiarity of such nervous regulation is that one branch of the motor nerve controls the work of a very small number of muscle fibers, which allows for maximum accuracy in eye movements.

The movements of the eyeball depend entirely on the characteristics of the muscle attachment. The attachment zone of the external and internal rectus muscles corresponds to the horizontal plane of the eyeball, which provides horizontal movements: turning them towards the nose (contraction of the internal rectus muscle) or towards the temple (contraction of the external rectus muscle).

The inferior and superior rectus muscles provide mainly vertical eye movements, but due to the fact that the line of muscle attachment is localized somewhat obliquely in relation to the limbus line, along with the vertical movement of the eyes, their inward movement also occurs.

The oblique muscles, when contracting, cause more complex movements, this is due to certain features of the location of the muscles, as well as their attachment to the sclera. The function of the superior oblique muscle is to lower the eye and turn it outward, and the function of the inferior oblique muscle is to lift it and move it outward.

At the same time, the superior and inferior rectus muscles and oblique muscles are capable of providing slight rotations of the eye clockwise or counterclockwise. Good nervous regulation, as well as coordinated work of the muscles of the eyeball, make it possible to perform complex movements: unilateral or directed in different directions, which ensures the volume and quality of vision, its binocularity.

Video about the structure of the eye muscles

Diagnostic methods

• Visual study of eye mobility, assessing the completeness of movements when tracking a moving object.
• Strabometry is an assessment of the angle of deviation of the eye during strabismus from the midline.
• A test with alternate covering of the eyes, which determines hidden strabismus - heterophoria, and in the case of obvious strabismus, determines its type.
• Ultrasound diagnostics to determine lesions of the oculomotor muscles localized close to the eyeball.
• Magnetic resonance imaging, computed tomography - identification of lesions of the oculomotor muscles throughout.

Symptoms of diseases

• Double vision - the condition can be caused by obvious strabismus or severe hidden strabismus.
• Nystagmus - occurs due to a violation of the ability to fix objects with the gaze.
• Impaired conjugal eye movement, limited mobility of the affected eye.
• Pain that increases with eye movement.
• Drooping eyelid.
• Impaired binocular vision.

Diseases affecting the muscles of the eye

• Strabismus.
• Ptosis.
• Muscle inflammation (myositis).
• Lagophthalmos.
• Blepharospasm.
• Heterophoria.
• Refractive error (myopia, hypermetropia).

The extraocular muscles are innervated by the III, IV and VI pairs of cranial nerves.

Oculomotor, or III cranial nerve. The third nerve (n. osiioshoi-gish) is mixed and includes motor and parasympathetic portions (Fig. 1.6).

Looking up and outwards M. rectus superior

Looking up and inward M. obliquus inferior

Outward movement of the eye (abduction) m. rectus

Inward eye movement

(cast)

Looking down and outwards M. rectus inferior

Looking down and inward M. obliquus superior

• - Somatic motor fibers
• - Preganglionic fibers Postganglionic fibers

All rectus muscles except the lateralis;

inferior oblique muscle;

muscle that lifts the upper eyelid

Rice. 1.6.

Motor portion innervates four of the six extraocular muscles of the eye and the muscle that lifts the upper eyelid. Vegetative parasympathetic portion innervates the smooth (intrinsic) muscles of the eye.

The nuclear complex of the III cranial nerve is located in the tegmentum of the mesencephalon at the level of the superior colliculi of the quadrigemina near the midline, ventral to the aqueduct of Sylvius.

This complex includes paired somatic motor and parasympathetic nuclei. The parasympathetic nuclei include: the paired accessory nucleus (n. oculomotorius accessorius), also called the Yakubovich-Edinger-Westphal nucleus, and the unpaired central nucleus of Perlia, located in the middle between the accessory nuclei.

The nuclei of the oculomotor nerve, through the fibers of the posterior longitudinal fascicle (fasc. longitudinalis posterior), are connected with the nuclei of the trochlear and abducens nerves, the system of vestibular and auditory nuclei, the nucleus of the facial nerve and the anterior nuclei of the spinal cord. The axons of the neurons of the nuclear complex go in the ventral direction, pass through the ipsilateral red nucleus and emerge on the surface of the brain in the interpeduncular fossa fossa interpeduncularis at the border of the midbrain and the Varoliev bridge in the form of a trunk of the oculomotor nerve.

The trunk of the III nerve pierces the dura mater in front and lateral to the posterior sphenoid process (processus clinoideus posterior), runs along the lateral wall of the cavernous sinus and then enters the orbit through the fissura orbitalis superior (Fig. 1.7, 1.8).

Processus clinoideus posterior

Rice. 1.7. Places of passage of cranial nerves on the internal base of the skull

Fissura orbitalis superior

Foramen rotundum

Foramen spinosum

Porusacusticus internus

Foramen jugulare

Canalis hypoglossalis

In the orbit, the III nerve is located below the IV nerve and such branches of the I branch of the V nerve, such as the lacrimal nerve (n. lacrimalis) and the frontal nerve (n. frontalis). The nasociliary nerve (p. nasociliaris) is located between the two branches of the III nerve (Fig. 1.9, 1.10).

N. oculomotorius N. trochlearis

N. ophthalmicus N. abducens N. maxillaris

Sinus cavernosus

Sinus sphenoidalis

Rice. 1.8. Diagram of the relationship between the cavernous sinus and other anatomical structures, section in the frontal plane (according to Drake R. et al., Gray’s Anatomy, 2007)

M. rectus superior

M. rectus lateralis

M. rectus inferior

M. obliquus inferior

M. obliquus superior

M. rectus medialis

Rice. 1.9. Extrinsic muscles of the eye, anterior view of the right orbit

Entering the orbit, the oculomotor nerve divides into two branches. The superior branch (the smallest) passes medially and above the optic nerve (n. opticus) and supplies the superior rectus muscle (m. rectus superior) and the muscle that lifts the upper eyelid (i.e. levator palpebrae superioris). The lower branch, which is larger, is divided into three branches. The first of them goes under the optic nerve to the medial rectus muscle (m. rectus medialis); the other - to the inferior rectus muscle (m. rectus inferior), and the third, the longest, follows forward between the inferior and lateral rectus muscles to the inferior oblique muscle (m. obliquus inferior). From here comes a short thick connecting branch - the short root of the ciliary ganglion (radix oculomotoria parasympathetica), carrying preganglionic fibers to the lower part of the ciliary ganglion.

glia (ganglion ciliare), from which postganglionic parasympathetic fibers for m. sphincter pupillae and m. ciliaris (Fig. 1.11).

N. oculomotorius, upper branch -

N. oculomotorius, lower branch

Rice. 1.10.

NN. ciliares longi

M. obliquus superior

M. levator palpebrae superioris

M. rectus superior

Ramus superior nervi oculomotorii

A. carotis interna

Plexus caroticus catoricus

N. oculomotorius

NN. ciliares breves

Ganglion trigeminale

M. rectus inferior

Ganglion ciliare

M. obliquus inferior

Ramus inferior nervi oculomotorii

Rice. 1.11. Branches of the oculomotor nerve in the orbit, lateral view (http://www.med.yale.edu/

caim/cnerves/cn3/cn3_1.html)

The ciliary ganglion (ganglion ciliare) is located near the superior orbital fissure in the thickness of the fatty tissue at the lateral semicircle of the optic nerve.

In addition, in transit through the ciliary ganglion, without interruption, pass fibers that conduct general sensitivity (branches of the nasociliary nerve from the V nerve) and sympathetic postganglionic fibers from the internal carotid plexus.

Thus, the motor somatic part of the oculomotor nerve includes a complex of motor nuclei and axons of the neurons that make up these nuclei, which innervate the muscles of the oculomotor. levator palpebrae superioris, m. rectus superior, m. rectus medialis, m. rectus inferior, m. obliquus inferior.

The parasympathetic part of the oculomotor nerve is represented by its parasympathetic nuclei, the axons of their cells (preganglionic fibers), the ciliary ganglion and the processes of the cells of this node (postganglionic fibers), which innervate the sphincter pupillae and the ciliary muscle (m. ciliaris). In other words, each Yakubovich-Edinger-Westphal nucleus contains the bodies of preganglionic parasympathetic neurons, the axons of which go as part of the trunk of the third cranial nerve, in the orbit they pass along with its lower branch and reach the ciliary (ciliary) ganglion (see Fig. 1.11). Axons of ciliary ganglion neurons (postganglionic fibers) form short ciliary nerves (nn. ciliares breves), and the latter pass through the sclera, enter the perichoroidal space, penetrate the iris and enter the sphincter muscle in separate radial bundles, innervating it sectorally. The unpaired parasympathetic nucleus of Perlia also contains the bodies of preganglionic parasympathetic neurons; their axons switch in the ciliary ganglion, and the processes of its cells innervate the ciliary muscle. It is believed that the Perlia nucleus is directly related to ensuring the convergence of the eyes.

Parasympathetic fibers coming from the Yakubovich-Edinger-Westphal nuclei constitute the efferent part of the reflex reactions of pupil constriction (Fig. 1.12).

Normally, pupil constriction occurs: 1) in response to direct lighting (direct reaction of the pupil to light); 2) in response to illumination of the other eye (reaction to light friendly with the other pupil); 3) when focusing the gaze on a nearby object (pupil reaction to convergence and accommodation).

The afferent part of the reflex arc of the pupil's reaction to light starts from the cones and rods of the retina and is represented by fibers that go as part of the optic nerve, then cross in the chiasm and pass into the optic tracts. Without entering the external geniculate bodies, these fibers, after partial decussation, pass into the handle of the superior colliculus of the midbrain roof plate (brachium quadrigeminum) and end at the cells of the pretectal region (area pretectalis), which send their axons to the nuclei

Yakubovich-Edinger-Westphal. Afferent fibers from the macula of the retina of each eye are represented in both Yakubovich-Edinger-Westphal nuclei.

Rice. 1.12.

E.J., Stewart P.A., 1998)

The efferent pathway of innervation of the sphincter of the pupil, described above, begins from the Ya Kubovich-Edinger-Westphal nuclei (see Fig. 1.12).

The mechanisms of the pupil's response to accommodation and convergence are not well understood. It is possible that during convergence, contraction of the medial rectus muscles of the eye causes an increase in the proprioceptive impulses coming from them, which are transmitted through the trigeminal nerve system to the parasympathetic nuclei of the 111th nerve. As for accommodation, it is believed that it is stimulated by defocusing images of external objects on the retina, from where information is transmitted to the center of the eye's close position in the occipital lobe (Brodmann's 18th field). The efferent pathway of the pupillary response also ultimately includes parasympathetic fibers of the 111 pair on both sides.

The proximal part of the intracranial segment of the third nerve is supplied with blood from arterioles arising from the superior cerebellar artery.

terpi, the central branches of the posterior cerebral artery (thalamoperforating, mesencephalic paramedian and posterior villous arteries) and the posterior communicating artery. The distal part of the intracranial segment of the III nerve receives arterioles from the branches of the cavernous part of the ICA, in particular from the tentorial and inferior pituitary arteries (Fig. 1.13). The arteries give off small branches and form numerous anastomoses in the epineurium. Small vessels penetrate the perineurium and also anastomose with each other. Their terminal arterioles pass into the nerve fiber layer and form capillary plexuses along the entire length of the nerve.

A. chorioidea anterior

A. hypophysialis inferior

Rice. 1.13. Branches of the internal carotid artery (according to Gilroy A.M. et al., 2008)

The trochlear, or IV cranial, nerve (n. trochlearis) is purely motor. The nucleus of the trochlear nerve (nucl. n. trochlearis) lies in the tegmentum of the midbrain at the level of the lower colliculi of the quadrigeminal, i.e. below the level of the nuclei of the third nerve (Fig. 1.14).

The fibers of the trochlear nerve emerge on the dorsal surface of the midbrain under the lower tubercles of the quadrigeminal, cross, bend around the cerebral peduncle from the lateral side, follow under the tentorium of the cerebellum, enter the cavernous sinus, where they are located under the trunk of the III nerve (see Fig. 1.8), after exiting from which they pass into the orbit through the superior orbital fissure outward from the tendon ring of Zinn surrounding the optic nerve. The IV nerve innervates the superior oblique muscle of the opposite eye (see Fig. 1.9).

To the superior oblique muscle

Rice. 1.14. Course of trochlear nerve fibers at the level of the midbrain

The nucleus of the trochlear nerve through the fibers of the posterior longitudinal fascicle (fasc. longitudinalis posterior) is connected with the nuclei of the oculomotor and abducens nerves, the system of vestibular and auditory nuclei, and the nucleus of the facial nerve.

Blood supply. The nucleus of the IV nerve is supplied by branches of the superior cerebellar artery. The trunk of the IV nerve is supplied with blood from the subpial arteries and the posterior lateral villous branch of the posterior cerebral artery, and at the level of the superior orbital fissure - by the branches of the external carotid artery (Schwartzman R.J., 2006)

The abducens, or VI, cranial nerve (n. abducens) is purely motor. Its only motor nucleus is located in the tegmentum of the Varoliev bridge under the bottom of the IV ventricle, in the rhomboid fossa (Fig. 1.15). The abducens nucleus also contains neurons that are connected through the medial longitudinal fasciculus to the nucleus of the oculomotor nerve, which innervates the medial rectus muscle of the contralateral eye.

The axons of the cells of the nucleus of the abducens nerve emerge from the substance of the brain between the edge of the pons and the pyramid of the medulla oblongata from the bulbar-pontine groove (Fig. 1.16).

In the subarachnoid space, the VI nerve is located between the pons and the occipital bone, ascending towards the pontine cistern lateral to the basilar artery. Next, it pierces the dura mater slightly below and outward from the posterior sphenoid process (Fig. 1.17), follows in the Dorello canal, which is located under the ossified petro-sphenoid ligament of Gruber (this ligament connects the apex of the pyramid with the posterior sphenoid process -

lump of the main bone), and penetrates the cavernous sinus. In the cavernous sinus, the abducens nerve is adjacent to the III and IV cranial nerves, the first and second branches of the trigeminal nerve, as well as the ICA (see Fig. 1.8). After leaving the cavernous sinus, the abducens nerve enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye, which rotates the eyeball outward.

Rice. 1.15.

Abductor

Rice. 1.1V. Position of the abducens nerve on the ventral surface of the brainstem

brain (according to Drake R. et al., Gray’s Anatomy, 2007)

Direction of the course of the VI nerve in the cranial cavity

The muscles of the eye perform coordinated movements of the eyeballs, providing high-quality and three-dimensional vision.

There are only six oculomotor muscles in the eye, of which four are direct and two are oblique, which received this name due to the peculiarities of the muscle’s course in the orbit and attachment to the eyeball. Muscle function is controlled by three cranial nerves: oculomotor, abducens and trochlear. Each muscle fiber of this muscle group is richly supplied with nerve endings, which ensures special clarity and precision in movements.

Thanks to the extraocular muscles, numerous options for the movement of the eyeballs are possible, both unidirectional: up, to the right, and so on; and multidirectional, for example, bringing the eyes together when working at close range. The essence of such movements is that, due to the coordinated work of the muscles, the same image of objects falls on the same parts of the retina - the macular area, providing good vision and a sense of the depth of space.

Features of the structure of the eye muscles

There are 6 extraocular muscles, of which 4 are rectus muscles, running in the forward direction: internal, external, superior and inferior. The remaining 2 are called oblique, as they have an oblique direction of movement and attachment to the eyeball - the superior and inferior oblique muscles.

All muscles, with the exception of the inferior oblique, begin from a dense connective tissue ring surrounding the external opening of the optic canal. Anterior to its origin, 5 muscles form a muscular funnel, inside which the optic nerve, blood vessels, and nerves pass. Next, the superior oblique muscle gradually deviates upward and inward, following the so-called trochlea. At this point, the muscle passes into a tendon, which is thrown through the pulley loop and changes its direction to oblique, attaching in the upper outer quadrant of the eyeball under the superior rectus muscle. The inferior oblique muscle begins at the inferior inner edge of the orbit, runs outward and posteriorly under the inferior rectus muscle, and is inserted in the inferior outer quadrant of the eyeball.

Approaching the eyeball, the muscles are surrounded by a dense capsule - Tenon's membrane and join the sclera at different distances from the limbus. The closest of the rectus muscles to the limbus is the internal one, and then the superior rectus muscle, while the oblique muscles are attached to the eyeball slightly posterior to the equator, that is, the middle of the length of the eyeball.

The work of the muscles is regulated, for the most part, by the oculomotor nerve: the superior, internal, inferior rectus and inferior oblique muscles, with the exception of the external rectus muscle, the work of which is provided by the abducens nerve and the superior oblique - trochlear nerve. A peculiarity of nervous regulation is that one branch of the motor nerve controls the work of a very small number of muscle fibers, due to which maximum accuracy is achieved when moving the eyes.

The movements of the eyeball depend on the characteristics of muscle attachment. The attachment points of the internal and external rectus muscles coincide with the horizontal plane of the eyeball, due to this horizontal movements of the eye are possible: turning to the nose when the internal rectus muscle contracts and to the temple when the external rectus muscle contracts.

The superior and inferior rectus muscles mainly provide vertical eye movements, but since the line of muscle attachment is located somewhat obliquely in relation to the limbus line, simultaneously with the vertical movement, the eye also moves inwards.

When contracted, the oblique muscles cause more complex actions, this is due to the peculiarities of the location of the muscles and their attachment to the sclera. The superior oblique muscle lowers the eye and rotates it outward, and the inferior oblique muscle lifts it and also abducts it outward.

In addition, the superior and inferior rectus muscles, as well as the oblique muscles, provide slight rotations of the eyeball clockwise and counterclockwise. Thanks to good nervous regulation and coordinated work of the muscles of the eyeball, complex movements are possible, both unilateral and directed in different directions, due to which three-dimensional vision, or binocularity, occurs, and, in addition, the quality of vision improves.

Diagnostic methods

• Determination of eye mobility - the completeness of eye movements when tracking a moving object is assessed.
• Strabometry is an assessment of the angle or degree of deviation of the eyeball from the midline in case of strabismus.
• Covering test - one and the other eye are alternately covered to determine hidden strabismus - heterophoria, and in case of obvious strabismus, its type is determined.
• Ultrasound diagnostics – determination of changes in the extraocular muscles in close proximity to the eyeball.
• Computed tomography, magnetic resonance imaging - detection of changes in the extraocular muscles along their entire length.

Symptoms of diseases

• Double vision is possible with obvious strabismus and with severe hidden strabismus.
• Nystagmus occurs when the ability of the eyes to fixate objects is impaired.