The The oculomotor nerveoculomotor nerve is the third of twelve is the third of twelve paired paired cranial nervescranial nerves. It controls most of the . It controls most of the

eye movementseye movements (cranial nerves (cranial nerves IVIV and and VIVI also do some), constriction of the pupil, and also do some), constriction of the pupil, and

holding the eyelid openholding the eyelid open

PathPath

NucleiNucleiThe fibers of the The fibers of the oculomotoroculomotor nerve nerve arise from a nucleus in the arise from a nucleus in the midbrainmidbrain, which , which

lies in the gray substance of the floor of the lies in the gray substance of the floor of the cerebral aqueductcerebral aqueduct and extends in and extends in front of the aqueduct for a short distance into the floor of the front of the aqueduct for a short distance into the floor of the third ventriclethird ventricle. . From this nucleus the fibers pass forward through the From this nucleus the fibers pass forward through the tegmentumtegmentum, the , the red nucleusred nucleus, and the medial part of the , and the medial part of the substantia nigrasubstantia nigra, forming a series of , forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the the medial side of the cerebral pedunclecerebral peduncle..

The nucleus of the oculomotor nerve does not consist of a continuous column of 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 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 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, 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. 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-The anterior group consists of two nuclei, an antero-medial and an antero-lateral .lateral .

The nucleus of the oculomotor nerve, considered from a physiological The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several smaller groups of cells, each group standpoint, can be subdivided into several smaller groups of cells, each group controlling a particular muscle.controlling a particular muscle.

A nearby nucleus, the A nearby nucleus, the EdingerEdinger--WestphalWestphal nucleus nucleus, is responsible for the autonomic functions of the , is responsible for the autonomic functions of the oculomotor nerve, including oculomotor nerve, including pupillarypupillary constriction and lens accommodation constriction and lens accommodation

The oculomotor nerve arises from the anterior aspect of The oculomotor nerve arises from the anterior aspect of mesencephalonmesencephalon (midbrain). There are two nuclei for the (midbrain). There are two nuclei for the

oculomotor nerve:oculomotor nerve:

The The oculomotor nucleusoculomotor nucleus originates at the level of the originates at the level of the superior colliculussuperior colliculus. The muscles it controls are the . The muscles it controls are the ciliary muscleciliary muscle (affecting (affecting accommodationaccommodation), and all ), and all extraocular musclesextraocular muscles except for the except for the superior oblique musclesuperior oblique muscle and the and the lateral rectus musclelateral rectus muscle..

The The Edinger-Edinger-Westphal nucleusWestphal nucleus supplies supplies parasympatheticparasympathetic fibres to the eye via the fibres to the eye via the ciliary ganglionciliary ganglion, and thus controls , and thus controls pupil constrictionpupil constriction..

Superior and inferior ramiSuperior and inferior rami the the superior branch of the oculomotor nervesuperior branch of the oculomotor nerve or the or the

superior divisionsuperior division, the smaller, passes medialward over , the smaller, passes medialward over the the optic nerveoptic nerve..

It supplies the It supplies the SuperiorSuperior rectus rectus and and Levator palpebrae superiorisLevator palpebrae superioris

The The inferior branch of the oculomotor nerveinferior branch of the oculomotor nerve or the or the inferior inferior divisiondivision, the larger, divides into three branches., the larger, divides into three branches.

One passes beneath the optic nerve to the One passes beneath the optic nerve to the medial rectusmedial rectus.. Another, to the Another, to the inferior rectusinferior rectus.. The third and longest runs forward between the inferior recti and lateralis to the The third and longest runs forward between the inferior recti and lateralis to the

inferior obliqueinferior oblique. From the last a short thick branch is given off to the lower part of . From the last a short thick branch is given off to the lower part of the the ciliary ganglionciliary ganglion, and forms its short root., and forms its short root.

Testing the oculomotor nerveTesting the oculomotor nerve Eye musclesEye muscles Cranial nerves III, IV and VI are usually tested together. The examiner Cranial nerves III, IV and VI are usually tested together. The examiner

typically instructs the patient to hold his head still and follow only with typically instructs the patient to hold his head still and follow only with the eyes a finger or penlight that circumscribes a large "H" in front of the eyes a finger or penlight that circumscribes a large "H" in front of the patient. By observing the the patient. By observing the eye movementseye movements and and eyelidseyelids, the examiner , the examiner is able to obtain more information about the is able to obtain more information about the extraocularextraocular muscles muscles, the , the levator palpebrae superioris muscle, and cranial nerves III, IV, and VI.levator palpebrae superioris muscle, and cranial nerves III, IV, and VI.

Since the oculomotor nerve controls most of the eye muscles, it may be Since the oculomotor nerve controls most of the eye muscles, it may be easier to detect damage to it. Damage to this nerve, termed easier to detect damage to it. Damage to this nerve, termed oculomotor nerve palsyoculomotor nerve palsy is also known by the is also known by the down n' outdown n' out symptoms, symptoms, because of the position of the affected eye.because of the position of the affected eye.

Pupillary reflexPupillary reflex The oculomotor nerve also controls the constriction of the pupils. This The oculomotor nerve also controls the constriction of the pupils. This

can be tested in two main ways. By moving a finger towards a person's can be tested in two main ways. By moving a finger towards a person's face to induce accommodation, as well as them going cross-eyed, their face to induce accommodation, as well as them going cross-eyed, their pupils should constrict.pupils should constrict.

Shining a light into their eyes should also make their pupils constrict. Shining a light into their eyes should also make their pupils constrict. Both pupils should constrict at the same time, independent of what eye Both pupils should constrict at the same time, independent of what eye the light is actually shone on.the light is actually shone on.