OCCULOMOTOR NERVE

It is the 3rd Cranial Nerve.

It’s a motor nerve
It supplies the following extrinsic muscles of the orbit
Levator palpebrae superioris
Superior, Medial, Inferior Rectus
Inferior Oblique
Also
Sphincter pupillae and Ciliary muscles with parasympathetic fibers. (Arising from Edinger Westphal nucleus)


FUNCTIONAL COMPONENTS

Somatic Efferent for the movements of eye ball. Fibers arise from the Occulomotor nucleus which is situated in ventromedial part of central grey matter of the midbrain at the level of superior colliculus.

General Visceral Efferent (parasympathetic), for contraction of the pupil and accommodation. Fibers arise from the Edinger Westphal nucleus (that lies in mid brain close to Occulomotor nucleus) passes through the Occulomotor nerve to the ciliary ganglion to supply Sphincter pupillae and ciliary muscle.

General Somatic Afferent for the proprioceptive impulses from the muscles of the eyeball. These impulses are relayed to the mesencephalic nucleus of trigeminal nerve.



ORIGIN
It emerges from the anterior aspect of midbrain medial to the cerebral peduncle, passes close to and between posterior cerebral and superior cerebellar arteries, runs forward in the lateral wall of cavernous sinus and divide into the superior and inferior ramus.
It enters the orbit through the superior orbital fissure.

Superior Ramus
Supply superior rectus muscle, then it pierces and supplies overhanging levator palpebrae superioris.

Inferior Ramus
It enters the orbit, gives off branches to inferior rectus, medial rectus, and inferior oblique.
Nerve to inferior oblique gives off a branch that passes to the ciliary ganglion and carries parasympathetic fibers to sphincter pupillae and ciliary muscles



PARALYSIS

COMPLETE PARALYSIS
In complete and total paralysis of 3rd nerve eye cannot move upward, downward or inward..It results in ptosis (i.e. drooping of the upper eyelid), lateral squint, dilation of the pupil; loss of accommodation; slight proptosis (i.e. forward projection of the eye); diplopia (double vision)

External Strabismus or Lateral Squint
At rest eye looks laterally because of activity of lateral rectus and downwards because of superior oblique.

SUPRANUCLEAR PARALYSIS OF 3rd NERVE
It causes loss of conjugate movement of eyes

WEBER’S SYNDROME
A midbrain lesion causing contra lateral hemiplagia and ipsilateral paralysis of 3rd nerve is known as Weber’s Syndrome.

SQUINT OR STRABISMUS
It may be concomitant or paralytic.
Concomitant Squint
Concomitant squint is congenital; there is no limitation of movement or no diplopia.
Paralytic Squint
In paralytic squint movement of eye ball is limited, diplopia and vertigo are present. The head is turned in the direction of function of paralyzed muscle. There is false orientation of field of vision.

DIPLOPIA
Patient sees double

PTOSIS
Drooping of upper eyelid due to paralysis of levator palpebrae superioris.

LOSS OF ACCOMODATION
Pupil is widely dilated and non reactive to light because of paralysis of sphincter pupillae and unopposed action of dilator pupillae (supplied by Sympathetic)

CILIARY GANGLION
· It is a peripheral parasympathetic ganglion placed in the course of occulomotor nerve.
· It lies near the apex of the orbit between optic nerve and lateral rectus.
· It has motor, sensory and sympathetic roots

MOTOR ROOT

It arises from nerve to inferior oblique, contains preganglionic fibers that begin in Edenger Westphal nucleus.
The fibers relay in ganglion, pass through short ciliary nerves and supply sphincter pupillae and ciliaris muscle .

SENSORY ROOT
It comes from the nasociliary nerve contains sensory fibers from eyeball.
The fibers do not relay in the ganglion.

SYMPATHETIC ROOT
It arises from the internal carotid plexus, contains post ganglionic fibers arising in the superior cervical sympathetic ganglion. The fibers do not relay in the ciliary ganglion. They pass out of the ganglion in short ciliary nerves and supply the blood vessels of the eye ball. They may also supply dilater pupallae.

BRANCHES

Ganglion gives 8 – 10 short Ciliary nerves that divide to 15 – 20 branches. They pierce sclera around the entrance of optic nerve; contain fibers from all the three roots of the ganglion.