Abduction nerve: description, anatomy, functions and features

The abducent nerve refers to the apparatus that regulates the movement of the eyes. His role there is not as significant as oculomotor, but in the event of a loss of function, the ability to see to some extent is lost. For the friendly movement of eyeballs, six muscles are needed, which are innervated by three cranial nerves.

Anatomy

The abducent nerve refers to the pure motor nerves. It begins in the nucleus, which is located in the middle brain. Its fibers through the bridge descend to the basal surface of the brain and move further along the furrow between the variolium bridge and the pyramids located in the medulla oblongata.

The processes of the nucleus pass through the membranes of the brain and turn out to be in the cavernous sinus. There, the fibers are located on the outside of the carotid artery. After the nerve has left the sine, it enters the upper orbital slot and finally reaches the orbit. The retracting nerve innervates only one muscle - a straight lateral one.

Function

The diverting nerve provides the only function performed by the muscle, which is innervated, namely, it removes the eye from the outside. This allows you to look around without turning your head. And also this muscle is an antagonist of the inner rectus of the eye, which pulls the eyeball toward the center, towards the nose. They compensate each other.

However, when one of them is damaged, there is a converging or diverging strabismus, since the healthy muscle will dominate and, cutting, turn the eyeball in its direction. The diverting nerve is paired, so friendly eye movement and binocular vision are provided .

Study

It is not possible to check the isolated nerve and its function at the present stage of the development of medicine. Therefore, neuropathologists and ophthalmologists examine all three nerves at once : oculomotor, diverting and block. This gives a more complete picture of the lesion.

Begin, as a rule, with complaints of double vision in the eyes, which increases when looking at the affected side. Then a visual examination of the patient's face is carried out, in order to determine its symmetry, the presence of swelling, redness and other manifestations of the inflammatory process. After that, they separately study the eyes for the object of protrusion or glancing of the eyeball, the descent of the upper eyelid.

Be sure to compare the width of the pupils and their reaction to light (friendly or not), convergence and accommodation. Convergence is the ability to focus on a closely located object. In order to check it, a pencil or a hammer is brought to the bridge of the nose. Normally, the pupils should narrow. The study of accommodation is carried out for each eye separately, but according to the technique of execution it resembles the verification of convergence.

Only after all these preliminary manipulations check, whether the patient has strabismus. And if there is, then which one. Then they ask the person to follow the eyes of the tip of the neurological malleus. This allows you to determine the amount of movement of the eyeballs. Withdrawing the malleus to the extreme points of the field of vision and holding it in this position, the doctor provokes the appearance of a horizontal nystagmus. If the patient has a pathology of the muscular apparatus of the eye, the pathological nystagmus (small horizontal or vertical eye movements) will not keep you waiting.

Defeat of the nerve

As already known, the nerve of the eye is responsible for turning the eyeball outward from the bridge of the nose. Violation of the conductivity of the nerve leads to a violation of the mobility of the direct lateral muscle. This causes convergent strabismus due to the fact that the inner muscle pulls on the eyeball. Clinically, this causes doubling in the eyes or scientific, diplopia. If the patient tries to look at the affected side, then this symptom is strengthened.

Sometimes other pathological phenomena are observed. For example, dizziness, gait disturbance and orientation in space. In order to see normally, patients, as a rule, cover their sore eyes. The defeat of the nerve alone is extremely rare, as a rule, it is a combination pathology.

Nuclear and peripheral paralysis

Neuropathy of the abducent nerve in its peripheral region occurs with meningitis, inflammation of the paranasal sinuses, cavernous sinus thrombosis, aneurysms of the intracranial segment of the carotid artery or posterior connective artery, fracture of the base of the skull or orbit, and tumors. In addition, toxic effects in botulism and diphtheria can also damage brain structures, including cranial nerves. Peripheral paralysis of the nerve is also possible with mastoiditis. In patients, the Gradenigo syndrome is observed: paresis of the nerve of the eye in combination with pain in the place of exit of the frontal branch of the trigeminal nerve.

Most often, nuclear disturbances occur against encephalitis, neurosyphilis, multiple sclerosis, hemorrhages, tumors, or chronic cerebrovascular disorders. Since the diverting and facial nerve are located side by side, the defeat of one, causes the pathology of the neighboring one. There is a so-called alternating Fauville syndrome (paresis of a part of the facial muscles on the affected side and a decrease in movements in the half of the trunk on the other side).

Bilateral defeat

The paresis of the nerve from both sides is manifested by a convergent strabismus. This condition occurs most often with increased intracranial pressure. If the amount of CSF is excessive, then a dislocation of the brain can be observed, that is, the clinging of the brain substance to the ramp at the base of the skull. With this development of events, it is easy to suffer from distracting nerves. They just in this place go to the lower surface of the brain and are practically unprotected.

There are other brain dislocations that manifest similar symptoms:
- squeezing the tonsils into the occipitone-neck funnel of the dura mater;
- wedging of the cerebellum into the brain sail and others.

They are not compatible with life, so the presence of damage to the nerve is a pathological anatomical statement. In addition, it must be remembered that the weakness of the external rectus muscle is one of the symptoms of myasthenia gravis.