That is, the third pair of brain nerves, which are motor brain nerves, including somatic movement andVisceraExercise two fibers.It starts from the intercostal fossa on the ventral side of the midbrain, goes forward close to the notch edge of the tentorium cerebelli and the side of the posterior clinoid process of the sella turcica, passes through the upper part of the lateral wall of the cavernous sinus, enters the orbit through the supraorbital fissure, controls eye muscle movement, and participates in regulating reflex and pupillary light reflex.
The oculomotor nucleus is located in the ventral gray matter around the aqueduct at the level of the superior colliculus of the mesencephalon.The fibers from the nucleus pass through the medial longitudinal tract, the red nucleus and the substantia nigra ventrally, leaving the brain stem at the medial side of the cerebral foot, between the posterior cerebral artery and the superior cerebellar artery.It passes through the dura mater near the posterior clinoid process of the sella turcica in a small triangle between the free and fixed edges of the tentorium cerebelli, enters the cavernous sinus, is located at the outer upper corner of the sinus, and then divides into two branches through the supraorbital fissure to enter the orbit.The upper branch supplies the levator palpebrae superioris and rectus superioris, and occasionally some fibers reach the orbicularis oculi;The inferior branch supplies the medial rectus, inferior rectus and inferior oblique muscles, and provides the short root of the ciliary ganglion. The latter's postganglionic fibers form the short ciliary nerve to supply the pupillary sphincter and ciliary muscle.
The oculomotor nucleus can be divided into three parts: the main nucleus of the lateral nucleus is the largest and contains a group of large neurons, which innervate the levator palpebrae superioris, rectus superioris, rectus medius, oblique inferior and rectus inferior muscles. However, the location of the nucleus innervating each eye muscle and its intersection have not been clarified.The paired Ai Wei nuclei are located at the posterior and medial sides of the lateral nucleus and are composed of smaller neurons. Their fibers innervate the pupillary sphincter and ciliary muscles.There are also medial nuclei between the lateral side, Aiwei nucleus and medial nucleus belong to the parasympathetic nervous system. Through these nuclei, the oculomotor nerve participates in some pupillary reflex activities.
Anatomical structure:
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（1） Segments:
The researchers divided the oculomotor nerve into five segments, which are cisternal segment, petrosal segment, cavernous sinus segment, supraorbital fissure segment, and orbital segment. The segmentation criteria are: ① cisternal segment: after the oculomotor nerve leaves the midbrain, it exits the cerebral peduncle on the lateral surface of the intercostal fossa and runs to the anterolateral and upper part of the posterior clinoid process ligament. ②The petrous segment: from the posterior petrous process ligament to the dural entrance into the cavernous sinus. ③Cavernous sinus segment: from the oculomotor nerve entering the cavernous sinus to the lower or front edge of the anterior clinoid process tip. ④Supraorbital fissure segment: from the oculomotor nerve entering the supraorbital fissure to exiting the supraorbital fissure. ⑤Orbital segment: The oculomotor nerve innervates each eye muscle through the superior and inferior branches of the superior orbital fissure.
（2） Relationship between cistern segment and surrounding vessels:
The oculomotor nerve is closely related to the peripheral blood vessels after exiting the interpedullary fossa. The ventral blood vessels include the small branches at the end of the basilar artery, the superior cerebellar artery, the posterolateral pontine artery and the interpedullary perforating branches of these arteries.The superior cerebellar artery originates from the end of the basilar artery and runs laterally at the ventral level of the oculomotor nerve.The posterolateral pontine artery originates from the basilar artery at the caudal side of the superior cerebellar artery and runs outward at the level of the dorsal inferior side of the superior cerebellar artery, and is located at the caudal side of the oculomotor nerve.The perforating branch between the feet from the above artery enters the posterior part of the interpedullary fossa and walks on the ventral side of the root of the oculomotor nerve.
The blood vessels adjacent to the back of the cistern segment of the oculomotor nerve are mainly the posterior cerebral artery, the posterior communicating artery and the thalamus artery.The posterior cerebral artery is the terminal branch of the basilar artery, and the oculomotor nerve usually contacts the medial main trunk of its interpedullary fossa.The posterior communicating artery originates from the internal carotid artery, passes under the optic tract, and is anastomosed with the posterior cerebral artery. Generally, it is separated from the root of the oculomotor nerve by the posterior cerebral artery without contacting it.The thalamus artery generally originates from the caudal side of the origin of the posterior cerebral artery, runs between the posterior cerebral artery and the oculomotor nerve, and contacts it across the oculomotor nerve.The accessory colliculus artery is a branch of the colliculus artery, and part of it is also adjacent to the back of the cistern segment of the oculomotor nerve.In addition, the posterior medial choroidal artery, the mesencephalic and diencephalic perforating arteries are adjacent to the cistern segment of the oculomotor nerve.
