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
Involuntary
- 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.!