Anatomy & Organs

Nervus oculomotorius – structure, function & diseases

Oculomotor nerve

As the oculomotor nerve , the III. called cranial nerve. He controls numerous eye movements.

What is the oculomotor nerve?

The nervus oculomotorius ( eye movement nerve ) is one of the twelve pairs of cranial nerves . He forms the III. Cranial nerve and is responsible for the innervation of four of the six extraocular muscles . In addition, it moves two inner eye muscles and the eyelid lifter.

His work is primarily motorized. However, some parasympathetic parts are also present in it. These are noticeable in the accommodation. During this process, the ciliary muscle is controlled. In addition, together with the abducens nerve and trochlear nerve, the oculomotor nerve moves the eyeball .

Anatomy & Structure

The oculomotor nerve originates in the front part of the midbrain . It leaves this body region through the interpeduncular fossa. It crosses the dura mater (hard meninges) at the sella turcica , also called the Turkish saddle, and runs in an anterior direction along the side wall of the cavernous sinus .The oculomotor nerve enters the eye socket (orbita) through the upper eye socket fissure (fissura orbitalis superior). After crossing the tin ring (Anulus tendineus communis), which marks the origin of the eye muscles, the cranial nerve branches off into three branches. These are the inferior ramus, the superior somatomotor ramus, and the ciliary ganglion, which forms a general visceromotor branch. The musculus rectus inferior (straight lower eye muscle), the musculus rectus medialis (straight inner eye muscle) and the musculus obliquus inferior (oblique lower eye muscle) are supplied by the inferior ramus.

The innervation area of ​​the superior ramus is formed by the superior rectus muscle (straight upper eye muscle) and the levator palpebrae muscle. The branch in the ciliary ganglion is connected to the postganglionic neuron . It takes care of the supply of the musculus sphincter pupillae and the musculus ciliaris (ciliary muscle).

The oculomotor nerve is equipped with cranial nerve nuclei, which are called nucleus nervi oculomotorii and nucleus accessory nervi oculomotorii or nucleus Edinger-Westphal. The nucleus nervi oculomotorii forms the nucleus of the somatomotor fibers, while the nucleus Edinger-Westphal forms the nucleus for the general visceromotor fibers. The somatomotor fiber nucleus is found in the tegmentum of the midbrain (mesencephalon) at the superior colliculi level.

Each muscle supplied by the oculomotor nerve has its own subnucleus. However, the subnucleus of the levator palpebrae muscle is unpaired. For this reason, when one eye is closed, it is considered difficult to keep the other open. The nucleus acessorius nervi oculomotorii is located on the back of the nucleus nervi oculomotorii.

Function & Tasks

One of the tasks of the oculomotor nerve is to supply the eye muscles, which are important for the mobility of the eyeball. This allows the eyeball to be rotated in different directions. The muscle work is carried out so precisely that the image of the left and right eye is superimposed.

Regardless of the viewing angle, the same image is always fixed, which in turn ensures three-dimensional vision. The eye muscles and thus the oculomotor nerve are also important for accommodation, i.e. the change between near and far vision. In the context of accommodation, the parasympathetic part of the eye movement nerve becomes active, which takes over the control of the ciliary muscle. It also narrows the iris of the pupil through the sphincter. This process is called miosis .

The unpaired nucleus perlia nervus ocolumotorii is responsible for the special innervation of the musculus ciliaris, which in turn enables the accommodation of the eye.

Diseases

The oculomotor nerve can sometimes be affected by damage. One of the most common complaints is oculomotor nerve palsy, which is paralysis of the nerve that moves the eyes. What is meant by this is a cranial nerve disorder that affects men and women to the same extent.Physicians distinguish between an external and an internal oculomotor nerve palsy . Both unilateral and bilateral paralysis are possible. Likewise, other eye paralysis in the eye muscles can set in at the same time. Paralysis of the oculomotor nerve is caused by various causes. These are mostly circulatory disorders , aneurysms or tumors within the brainstem. In some cases, the oculomotor nerve palsy is also a side effect of other diseases. These primarily include Benedict’s syndrome, Weber’s syndrome or Nothnagel’s syndrome.

Furthermore, combination paralysis with the abducens nerve or trochlear nerve is possible. It is not uncommon for diabetics to suffer from paralysis of the oculomotor nerve. A significant symptom of oculomotor nerve palsy is absolute pupillary rigidity. In addition, the patients often squint and suffer from restricted movement of the eyes or perceive double vision. Furthermore, the accommodation of the eye is restricted. If there is an internal isolated oculomotor nerve palsy without involvement of the external eye muscles, doctors speak of ophthalmoplegia interna.

Another typical sign of oculomotor nerve palsy is the low level of the eye on which the paralysis occurs. There is a slight outward rotation of the eyes. Some patients also adopt a head restraint position in order to maintain binocular single vision.

Damage to the oculomotor nerve is treated by a neurologist . The chances of recovery depend on the cause of the disease. The prognosis is considered more favorable if the patient suffers from circulatory disorders. In the case of aneurysms or tumors, on the other hand, an unfavorable course is to be expected. In some cases, a squint operation is performed.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.