CN III, IV, VI

Question 1

Parasympathetics travelling on CN III innervate what structures?

Answer 1

Sphincter pupillae - Pupil constriction
and
Ciliary muscles - Lens acomodation.

Question 2

What is the pathway of the CN III from the brain?

Answer 2

Pieces the dura mater entering cavernous sinus passing through the superior orbital fissure to dissminate.

Question 3

Where is the occulomotor nucleus located?

Answer 3

Ventral to periaqueductal gray in rostral midbrain.

Contains motor neurons for CN III

Question 4

Where is teh Edinger- Wesphal nucleus located and what functions does it have?

Answer 4

Pre ganglionic parasympathetic neurons.

Question 5

Describe the Edinger-Wesphal nucleus pathway.

Answer 5

Pre-ganglionic parasympathetics joint the occulomotor nerve and synapse onto the ciliary ganglion.

Post ganglionic parasymps leave the ciliary ganglion and travel via the short ciliary fibers of CN V.

Question 6

Describe what occurs if the CN III is compressed

Answer 6

All muscles of the eye except for the lateral recturs and superior oblique are paralyzed.

Presents with:
Ptosis
Eye turns down and out due to lateral rectus and superior oblique.

Dilated pupil
Non-acomodating pupil.

Question 7

Describe Horners syndrome

Answer 7

Loss of sympathetic input:
Ptosis due to loss of Mullers muscl

Constricted pupil (Miosis) due to lack of sympathetic tone.

Question 8

Where is the trochlear nucleus located and what is its pathway to the SOM

Answer 8

Trochlear nucleus is located in the inferior colliculus in the cuadal midbrain where it will send nerves that desucate posteriorly and exit the brainstem inferior to inferior colliculus!

Question 9

Why is Trochlear nerve unique?

Answer 9

Longest Cranial nerve
Thinniest Cranial nerve
Dessucates
emerges from posterior aspect of brainstem.

Question 10

What occurs if there is a lesion to the trochlear nucleus?

Answer 10

Paralysis of the contralateral SO

Question 11

What happens if there is a lesion to the trochlear nerve after it leaves the brainstem?

Answer 11

Paralysis of the ipsilateral SO.

Question 12

What actions does the SOM have?

Answer 12

Intorsion, depression, and abduction.

Question 13

Damage to the trochlear nerve will cause the eye to move in which way?

Answer 13

Eye will become hypertropic.

This is worsened when looking at a book or walking down stairs.

Question 14

How can a person with a trochlar nerve injury compensate?

Answer 14

Tilting head to good side and tilting the chin down!

Question 15

Where is the abducens nuclei located and what other cell bodies are located in this area?

Answer 15

The abducens nuclei are located within the caudal pons.

The internuclear MLF cell bodies are also contained here that cross the midline to join the occulomotor nucleus in the rostral midbrain!

Question 16

What happens if the Abducens nerve is lesioned?

Answer 16

Ipsilateral lateral rectus become paralyzed causing the eye to drift medially (esotropia with medial strabismus causing horizontal diplopia.)

Question 17

What happens if there is a lesion to the abducens nuclei in the caudal pons?

Answer 17

Loss to lateral rectus ipsilaterally as well as loss of LMN to contralateral eye thus cannot move eyes conjugately horizontally.

Question 18

What occurs if the right MLF is damaged?

Answer 18

There is a disconnect between the left abducens nuclei and the right oculomotor nuclei.
Thus the left eye will abduct but the right eye will not adduct.

Question 19

Why is it that a patient that has lost an abducens nuclei is still able to converge eye sight on a pencil?

Answer 19

The supranuclear controls in the reticular formation are able to overide the system and activate the muscle.

Question 20

What is one and a half syndrome?

Answer 20

abducens nucleus completely desroyed on one side (including interneurons) = ipsilateral gaze paralysis when looking to side of lesion.

AND

Ipsilateral MLF fibers from contralateral nucleus are broken thus the eye is stuck and the other eye can only abduct!