CN 13 pt 1

Question 1

Nuclear and infranuclear pathways

Answer 1

CN III, IV, and VI nuclei, their peripheral nerves, and the extraocular muscles

Question 2

Supranuclear pathways

Answer 2

Brainstem and forebrain circuits that control eye movements

• Connect with CN III, IV, and VI nuclei

Question 3

Extraocular muscles that do horizontal movement

Answer 3

Lateral rectus

• Medial rectus

Question 4

Extraocular muscles producing vertical movement

Answer 4

Superior rectus

• Inferior rectus

Question 5

Extraocular muscles origin and insertion

Answer 5

Common tendinous ring at apex of orbit

Muscles insert into the sclera

Question 6

Oblique muscles

Answer 6

Torsional movements
• Eye is slightly rotated about its axis

Superior oblique
• Inserts on superior surface
• Produces primarily intorsion
• Movement of the upper pole of the eye inward (nasally)

Inferior oblique
• Inserts on inferior surface
• Produces primarily extorsion
• Movement of the upper pole of the eye outward (temporally)

Question 7

Movement produced by an extraocular muscle depends on…

Answer 7

the direction the muscle pulls relative to the main axis of the eye

Ie. With the eye adducted, the superior oblique causes depression

Question 8

Innervation of extraocular muscles

Answer 8

(LR6 SO4)3 …LR by CN VI, SO by CN IV, the rest supplied by CN III

Question 9

CN III has two major branches

Answer 9

Superior division

• Innervates levator palpebrae superior (elevates eyelid)
• Innervates superior rectus (SR)

Inferior division
-Contains parasympathetic fibers to pupillary constrictor muscles and
ciliary muscles of the lens
-Innervates the other extraocular muscles (except LR and SO)

Question 10

CN III, CN IV, and CN VI all travel through

Answer 10

cavernous sinus and enter the orbit via the superior orbital fissure

Question 11

Table 13.1

Answer 11

Go look at it on slide 7

Question 12

CN III: oculomotor nuclei

Answer 12

In upper midbrain (level of superior colliculi and anterior to PAG) CN III exits anteriorly between posterior cerebral artery and superior cerebellar artery

Question 13

CN III: oculomotor nuclei parasympathetic fibers

Answer 13

run in the superficial and medial portion of CN III

• Susceptible to compression from PComm aneurysms

Question 14

CN IV: trochlear nuclie

Answer 14

In lower midbrain (level of inferior colliculi and anterior to PAG)

Question 15

CN VI

Answer 15

Cross over each other before exiting the brainstem dorsally
• Susceptible to compression from cerebellar tumors
• Very thin and easily damaged by shear injury from head trauma

Question 16

CN VI: abducens nuclei

Answer 16

In mid/lower, posterior pons (floor of fourth ventricle) CN VI exits at the pontomedullary junction

Question 17

CN VI

Answer 17

Ascends and exits the dura to enter Dorello’s canal
• Has a long, ascending, vertical course to reach the orbit
• Highly susceptible to downward traction injury produced by
elevated ICP

Question 18

Diplopia

Answer 18

Double vision

caused by abnormalities in several locations
Mechanical problems
• Orbital fx with muscle entrapment •

The extraocular muscles
• Orbital myositis

The neuromuscular junction
• Myasthenia gravis (MG)

CN III, IV, VI and their central pathways
The supranuclear ocular pathways
• Ingestion of toxins
• Anticonvulsant medications

Question 19

Dysconjugate gaze

Answer 19

strabismus

Visual input normally helps maintain the eyes yoked in the same direction

Occurs when an extraocular muscle is not working properly, and
the result is diplopia

Question 20

Diplopia in kids

Answer 20

Conventional muscle weakness can produce dysnconjugate gaze

Over time will cause suppression of one of the images and result in amblyopia (decreased vision in one eye)

Early intervention!!

Question 21

Diplopia worse when

Answer 21

Looking at objects that are near because the medial rectus has been affected, need adduction of both eyes for near vision

Question 22

Common causes of oculomotor palsy (CN III)

Answer 22

Diabetic neuropathy
• Head trauma (shearing forces)
• Aneurysms (junction of PComm and ICA)
• Infection
• Tumor
• Infarct of the nucleus
• Herniation of temporal lobe (over edge of tentorium cerebelli)
• Lesions of CN III fascicles

Question 23

Oculomotor palsy (CN III)

Answer 23

Superior oblique and lateral rectus are left intact so the remaining movements are ABduction, In torsion, and depression.

The eye will rest in a “down and out” position

Levator palpabrae has been affected so eye lid closed

Loss of PS fibers that constrict pupil lead to dilation

Question 24

PComm aneurysm

Answer 24

Suspected w/ pts w/ painful CN III palsy involving pupil

Diagnosis until prove otherwise
Emergency CT angiogram needed immediately

Question 25

Trochlear palsy (CN IV)

Answer 25

Eye will rest hypertrophic and extortion

Vertical diplopia

Question 26

Diplopia can be improved by

Answer 26

Tucking chin and tilting head away from affected eye because these movements produce the movements that the eye muscles would normally do

Question 27

Common causes of trochlear palsy (CN IV)

Answer 27

Head trauma
• Very commonly injured CN with head trauma
• Neoplasm • Infection • Aneurysms • Microvascular damage (DM)

Question 28

Rln b/n compensatory head positions and eye movement abnormalities

Answer 28

Head movement is always in the direction of the action normally
produced by the affected muscle

• E.g. In a right CN IV palsy, the head down/chin tucked, and head tilted
to the left (CN IV actions are normally depression and intorsion)

Question 29

Abducens palsy (CN VI)

Answer 29

Horizontal diplopia because lesion to CN VI which normally causes eye abduction

Worse when looking at objects that are far because the lateral rectus cannot abduct both eyes

Question 30

Common causes of abducens palsy

Answer 30

Downward traction from elevated ICP
• Infection
• Neoplasm
• Aneurysms
• Microvascular damage (DM)
• Pontine infarcts can damage CN VI fascicles (affecting ipsilateral eye)
• Lesions of CN VI nucleus in pons will not produce a simple abducens
palsy, but instead a horizontal gaze palsy (movements of both eyes in one direction are decreased)

Question 31

Which way will your pt turn head in attempt to compensate for horizontal diplopia?

Answer 31

Toward the affected eye (lateral rotation of head)

Question 32

Light shown in one eye causes

Answer 32

1. Pupillary constriction (direct response) in that eye

2. Pupillary constriction (consensual response) in the other eye

Question 33

Light entering one eye activates

Answer 33

CN II which projects to the optic
tracts
• Extrageniculate fibers project to
the pretectal area of the
midbrain
• Synapse occurs at the pretectal
nuclei
Fibers then project bilaterally to synapse at the Edinger-Westphal nuclei
• Most fibers cross at the
posterior commissure
Preganglionic parasympathetic fibers arise bilaterally from the Edinger-Westphal nuclei and travel with CN III
Synapse occurs at the ciliary ganglia in the orbit
Postganglionic parasympathetic fibers then target pupillary constrictor muscles

Question 34

Pupillary light reflex review

Answer 34

Light entering one eye activates CN II, which then projects to both optic tracts to the pretectal area of the midbrain. After synapsing at the pretectal nuclei, fibers project bilaterally to the Edinger-Westphal nuclei, where preganglionic parasympathetic fibers will exit bilaterally to travel w/ CN III to synapse at the ciliary ganglion. After synapse, the post - ganglionic parasympathetic fibers project to the pupillary constrictormuscles of the iris.