CN III Flashcards
(28 cards)
CN III route?
Exits the interpendicular fossa of the midbrain. Passes between the posterior cerebral artery and superior cerebellar artery.
Runs lateral to which artery?
CN III runs laterally to the posterior communication Artery
It passes between the what?
anterior and posterior clinoid process attachments of tentorium cerebelli
It lies where where on the posterior clinoid process? How about the anterior clinoid process?
above posterior.
below anterior
Does it pass through the cavernous sinus? It is above what nerve.
Yes lateral to it. passes above the trochlear nerve (IV)
It enter the orbit through which fissure?
The superior orbital fissure
Where does CN III provide motor innervation?
To the skeletal muscles of the eye
What two different functions does the oculomotor nerve have?
- Levator palpebrae superioris which elevates the upper eyelid.
- The extraocular muscles that move the eyeball
- superior rectus
- medial rectus
- inferior rectus
- inferior oblique
Do CN III provide any other motor innervation?
Yes, the parasympathetic to two smooth muscles in the eye.
- sphincter muscles of the pupil-constricts the pupil
- ciliary body muscle contraction of this muscle changes the shape of the lend to allow a person to see clear at near (accommodation occurs)
CN III divides into what two divisions and where?
It divides into the superior and inferior division variable distance behind the globe (within the cavernous sinus)
The superior division innervates what?
the levator palpebrae superioris and superior rectus
The inferior division innervates what?
medial rectus
inferior rectus
inferior oblique
What is the process of the parasympathetic fibers in the CN III
they begin by being positioned superior and medial in the nerve (very superficial position). In order to maintain this superficial position they slowly shift to an inferior and medial location so they can travel in the inferior division of CN III
The blood supply to the nerves is located where? What is it called histologically?
Located in the center of the nerves. Called the vasa nervorum.
Action of the lateral rectus?
abducts the eye = turns the eye out- innervated by CN VI
Action of superior oblique muscle?
Turns the eye down and out - innervated by CN IV
Complete third nerve compression would cause what skeletal muscle affect?
levator palpebrae and superioris
Complete third nerve compression would cause what clinical sign?
large ptosis
Complete third nerve compression would cause what symptoms?
cant raise eyebrows, upper eyelid completely
Complete third nerve compression would affect which extra ocular muscles?
superior rectus, medial rectus, inferior rectus, inferior oblique
Complete third nerve compression would cause which smooth muscles?
SPH, ncter of pupil, dilated, photophobia, ciliary body muscles, cannot read near card to check vision at near, blur trying to read at near
What could cause the compression of the oculomotor nerve?
A tumor or hematoma that could push the temporal lobe medially towards the tentorial notch. if the temporal lobe herniates downward through the tentorial notch, CN III may be stretched compressed or both. there could be intracranial bleeding, raising the pressure and pushing the cerebral cortex.
What are signs of an aneurysm in the eye?
A dilated pupil, and a loss of accommodation cant see at near clearly.
What kinds of patients will have a CN III paralysis?
diabetes, hypertension, and or atherosclerosis.
