CN III

Question 1

CN III route?

Answer 1

Exits the interpendicular fossa of the midbrain. Passes between the posterior cerebral artery and superior cerebellar artery.

Question 2

Runs lateral to which artery?

Answer 2

CN III runs laterally to the posterior communication Artery

Question 3

It passes between the what?

Answer 3

anterior and posterior clinoid process attachments of tentorium cerebelli

Question 4

It lies where where on the posterior clinoid process? How about the anterior clinoid process?

Answer 4

above posterior.

below anterior

Question 5

Does it pass through the cavernous sinus? It is above what nerve.

Answer 5

Yes lateral to it. passes above the trochlear nerve (IV)

Question 6

It enter the orbit through which fissure?

Answer 6

The superior orbital fissure

Question 7

Where does CN III provide motor innervation?

Answer 7

To the skeletal muscles of the eye

Question 8

What two different functions does the oculomotor nerve have?

Answer 8

1. Levator palpebrae superioris which elevates the upper eyelid.
2. The extraocular muscles that move the eyeball
   - superior rectus
   - medial rectus
   - inferior rectus
   - inferior oblique

Question 9

Do CN III provide any other motor innervation?

Answer 9

Yes, the parasympathetic to two smooth muscles in the eye.

1. sphincter muscles of the pupil-constricts the pupil
2. ciliary body muscle contraction of this muscle changes the shape of the lend to allow a person to see clear at near (accommodation occurs)

Question 10

CN III divides into what two divisions and where?

Answer 10

It divides into the superior and inferior division variable distance behind the globe (within the cavernous sinus)

Question 11

The superior division innervates what?

Answer 11

the levator palpebrae superioris and superior rectus

Question 12

The inferior division innervates what?

Answer 12

medial rectus
inferior rectus
inferior oblique

Question 13

What is the process of the parasympathetic fibers in the CN III

Answer 13

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

Question 14

The blood supply to the nerves is located where? What is it called histologically?

Answer 14

Located in the center of the nerves. Called the vasa nervorum.

Question 15

Action of the lateral rectus?

Answer 15

abducts the eye = turns the eye out- innervated by CN VI

Question 16

Action of superior oblique muscle?

Answer 16

Turns the eye down and out - innervated by CN IV

Question 17

Complete third nerve compression would cause what skeletal muscle affect?

Answer 17

levator palpebrae and superioris

Question 18

Complete third nerve compression would cause what clinical sign?

Answer 18

large ptosis

Question 19

Complete third nerve compression would cause what symptoms?

Answer 19

cant raise eyebrows, upper eyelid completely

Question 20

Complete third nerve compression would affect which extra ocular muscles?

Answer 20

superior rectus, medial rectus, inferior rectus, inferior oblique

Question 21

Complete third nerve compression would cause which smooth muscles?

Answer 21

SPH, ncter of pupil, dilated, photophobia, ciliary body muscles, cannot read near card to check vision at near, blur trying to read at near

Question 22

What could cause the compression of the oculomotor nerve?

Answer 22

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.

Question 23

What are signs of an aneurysm in the eye?

Answer 23

A dilated pupil, and a loss of accommodation cant see at near clearly.

Question 24

What kinds of patients will have a CN III paralysis?

Answer 24

diabetes, hypertension, and or atherosclerosis.

Question 25

For a vascular disorder all the EOM’s would not be able to move the eyeball except for? And the person’s eye would be looking in what direction?

Answer 25

Except for the lateral rectus and superior oblique. the eye would be looking down and out.

Question 26

Would the levator palpebrae superiors muscle function? What would you notice the person has?

Answer 26

the muscle does not function and would notice a large ptosis.

Question 27

Would the parasympathetic fibers be affected?

Answer 27

Not necessarily, because of the peripheral location they might have.

Question 28

When the parasympathetic fibers are not affected the condition is called what? the most common cause is?

Answer 28

“pupil sparing” and cause is hypertension.