The oculomotor nerve is the next one for you to think about. It has two functional components.
First is a general somatic efferent component as it innervates skeletal muscles. Then there’s also a general
visceral efferent component for you to keep in mind.
The third cranial nerve leaves through the superior orbital fissure of the middle cranial fossa for its distribution.
With respect to general somatic efferent innervation,
the oculomotor nerve is responsible for innervating several of the extraocular muscles as well as a muscle
that elevates the upper eyelid. That muscle is termed the levator palpebrae superioris. You can see it
along here. Then you see its insertion into the upper eyelid right in through here. This muscle also
innervates the superior rectus which is shown right in through here inserting into the sclera of the eyeball.
The inferior oblique is innervated by this muscle as well. We see the oblique course of this muscle along
the side of the eyeball in this area. Inferior rectus is also innervated by the oculomotor which is labeled here.
Then we have the medial rectus muscle that is shown right in through here. General visceral efferents
are responsible for two functions. One is these fibers will innervate the sphincter muscle of the pupil
causing it to constrict. Then the second functional component here is that it will cause contraction of the
ciliary muscles which will allow for accommodation of the lens for near vision. Some clinical
considerations for you to think about with respect to the oculomotor nerve would be that a lesion of
this nerve can lead to dilation of the pupil since it’s no longer able to constrict it. Because of the numerous
extraocular eye muscles that the oculomotor nerve innervates, if there’s partial paralysis or paralysis of
these muscles, the eye tends to then move down and out. There’s an associated loss of the pupillary reflex.
Then because of the levator palpebrae superioris no longer being able to contract, there is a drooping
of the upper eyelid and that’s termed ptosis. Causes of these clinical features could be due to
a compression from a neighboring aneurysmal artery that puts pressure on the nerve causing it to demyelinate.
Tumors can impair the function of the oculomotor nerve causing it to lesion. Lack of blood supply to the
nucleus or to the oculomotor nerve fibers can cause infarction. A thrombosis in the cavernous sinus can
impinge upon the oculomotor nerve and cause impairment. Then meningitis, an inflammatory state, can also
involve the oculomotor nerve as well.