CRANIAL NERVE III: OCULOMOTOR NERVE

INFERIOR DIVISION: Somatic innervation to the medial and inferior rectus muscles.

• The inferior division also carries Parasympathetic Fibers, via the Short Ciliary Nerve, to the Sphincter Pupillae and Ciliary Muscles (constrict eye and accommodate for near vision).

UNILATERAL LESION OF OCULOMOTOR NERVE: Damage would be as follows.

1. "Lateral Strabismus" = the eyeball will point downward and outward.

Unchecked tension of the Lateral Rectus (CN VI) will abduct it (pull it outward)

• Unchecked tension of the Superior Oblique (CN IV) will pull the eye down and outward -- not upward!

1. "Ptosis" = the eyelid will droop.

• This is due to lost innervation of the Levator Palpebrae muscle.
• There may be tonic tension of the Frontalis Muscle as well, in order to compensate for drooping eyelid.

2. "Mydriasis" = The pupil will be dilated.

• Due to lost innervation of the Sphincter Pupillae.

3. Accommodation of the lens will be lost.

• Due to lost innervation to Ciliary Muscle.

Category: Anatomy Notes