NERVES OF EXTRAOCULAR MUSCLES
- The extraocular muscles, responsible for the movement of the eyeballs, are primarily innervated by 3 cranial nerves.
- * Each of the cranial nerves arises from a specific nucleus (a collection of nerve cell bodies) within the brainstem.
They pass through cavernous sinus (lateral wall).
* They (3 nerves) enter the orbital through the superior orbital fissure.
Oculomotor nerve(III) :
- Its functions are:
- Motor: to all extra-ocular muscles except 2 muscles (superior oblique and lateral rectus).
LR § so §
- Parasympathetic: to sphincter pupillae and ciliary muscles of the eye.
- So it has the following nuclei of origin:
- Motor nucleus: located in midbrain at the level of superior colliculus.
- Parasympathetic nucleus (Edinger Westephal nucleus): located in midbrain. It sends preganglionic parasympathetic fibers that relay in ciliary ganglion. The postganglionic fibers supply both sphincter pupillae and ciliary muscles.
Trochlear nerve (IV)
- Its function is:
- Motor: to one extra-ocular muscle (superior oblique).
- So it has only motor nucleus: located in midbrain at the level of inferior colliculus.
- N.B: each trochlear nerve emerge from back of midbrain, decussate with its fellow to supply the contralateral superior oblique muscle.
the only cranial n. 1.
pass through the cavity of the cavernous sinuses
Abducens nerves (VI) :
- Its function is:
- Motor: to one extra-ocular muscle (lateral rectus).
- So it has only motor nucleus: located in pons beneath the medial eminence of dorsal surface of pons.