Anatomy Dissected: Cranial Nerve III (oculomotor nerve)

Anatomy Dissected: Cranial Nerve III (oculomotor nerve)


Welcome back to our brand new series
Anatomy Dissected by Complete Anatomy Continuing on with our cranial nerve
series, it’s now time to take a look at Cranial Nerve III: the oculomotor nerve In this video will first explore the pathway of this nerve Examine the muscles it innervates and their functions and finish off by looking at some of the clinical correlates Let’s start at the brainstem, where a collection of both somatic and visceral motor axons exit on the anterior surface as the oculomotor nerve From here the nerve runs anteriorly in the subarachnoid space, piercing the dura and passing through the wall of
the cavernous sinus upon exiting the cavernous sinus the oculomotor nerve runs below the lesser wing of the sphenoid bone to enter the
orbit through the superior orbital fissure As the nerve enters the orbit, it divides into its superior and inferior branches Both branches will pass into the orbit within the boundaries of the common tendinous ring From here the superior and inferior branches will pass anteriorly to supply the extraocular
muscles of the eye. As we said already, this nerve carries both somatic and
autonomic nerve fibres Somatic functions of the nerve include movement of the eye and eyelid The muscles that are innervated by the oculomotor nerve are the Levator Palpebrae Superioris muscle which is responsible for elevating the
eyelid The Superior Rectus muscle which predominantly moves the eyeball
superiorly or elevators it. The Inferior Rectus muscle primarily depresses and adducts eyeball The Medial Rectus muscle adducts the eyeball, moving it towards the midline Finally, the Inferior Oblique muscle
elevates, abducts and laterally rotates the eyeball Autonomic functions of cranial
nerve III include control of the pupil and lens innervation to the Sphincter Pupillae muscle allows for pupil constriction This nerve also innovates the ciliary muscles which when contracted alters the curvature of the lens and and allows an individual to focus Like all of the nerves in the human body the oculomotor nerve can be damaged Though it has a relatively protected course through the base of the skull and in the orbit it has a number of vulnerable points increased pressure in the cavernous
sinus can force the nerve against other structures causing it to become
compressed An aneurysm of the posterior communicating artery can apply local pressure to the nerve close to its emergence from the brainstem reducing its functionality Compression or damage to the nerve results in oculomotor nerve palsy which commonly presents as ptosis a down and outward gaze and mydriasis in the affected eye So that’s it Hopefully now you have a much better
understanding of cranial nerve III You should now be able to discuss the
pathway of the nerve from the anterior surface of the brainstem all the way to
the muscles You should now be able to identify the muscles that rely on this
nerve and their functions and you should be familiar with some of the clinical
features and causes of cranial nerve 3 damage Remember to stay tuned for the rest of our series on cranial nerves Hit the like button below and subscribe for more top class anatomy content