The fibers of the oculomotor nerve arise from a nucleus in the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

, which lies in the gray substance of the floor of the

cerebral aqueduct The cerebral aqueduct (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is a conduit for cerebrospinal fluid (CSF) that connects the third ventricle to the fourth ventricle of the ventricular system of the br ...

and extends in front of the aqueduct for a short distance into the floor of the

third ventricle The third ventricle is one of the four connected ventricles of the ventricular system within the mammalian brain. It is a slit-like cavity formed in the diencephalon between the two thalami, in the midline between the right and left lateral ...

. From this nucleus the fibers pass forward through the

tegmentum The tegmentum (from Latin for "covering") is a general area within the brainstem. The tegmentum is the ventral part of the midbrain and the tectum is the dorsal part of the midbrain. It is located between the ventricular system and distinctive ba ...

, the

red nucleus The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. ...

, and the medial part of the substantia nigra, forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the

cerebral peduncle The cerebral peduncles are the two stalks that attach the cerebrum to the brainstem. They are structures at the front of the midbrain which arise from the ventral pons and contain the large ascending (sensory) and descending (motor) nerve tract ...

. The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on the two sides of the middle line, while the sixth is centrally placed and is common to the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral. The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several smaller groups of cells, each group controlling a particular muscle. A nearby nucleus, the Edinger-Westphal nucleus lies dorsal to the main oculomotor nucleus. It is responsible for the autonomic functions of the oculomotor nerve, including

pupil The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...

lary constriction and lens accommodation.

Additional images

File:Gray697.png, Nuclei of origin of cranial motor nerves schematically represented; lateral view. File:Gray710.png, Coronal section through mid-brain. File:Gray711.png, Transverse section of mid-brain at level of inferior colliculi. File:Gray774.png, Scheme showing central connections of the optic nerves and optic tracts. File:Gray775.png, Plan of oculomotor nerve. File:Gray785.png, Figure showing the mode of innervation of the Recti medialis and lateralis of the eye. File:ThreeNeuronArc.png , Vestibulo-ocular reflex

External links

* - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View" * * * {{Authority control Cranial nerve nuclei Oculomotor nerve Midbrain