CN's 3,4,6

Question 1

What type of nerves are CN’s 3,4 and 6

Answer 1

3: Somatic motor and Visceral motor
4: Somatic motor
6: Somatic motor

Question 2

CN 3 (Occulomotor):

1. Axon type(s)
2. CNS origin/termination
3. Peripheral origin/termination

Answer 2

1. Somatic motor
2. Occulomotor nucleus (Rostral midbrain)
3. Superior, inferior, medial recti, inferior oblique, and levator palpebrae superioris
4. Autonomic efferent
5. Edinger-Westphal nucleus
6. Pupillary sphincter, ciliary muscle (after synapse in ciliary ganglia)

Question 3

CN 4 (Trochlear):

1. Axon type(s)
2. CNS origin/termination
3. Peripheral origin/termination

Answer 3

1. Somatic motor
2. Trochlear nucleus (caudal midbrain)
3. Superior oblique

Question 4

CN 6 (Abducens):

1. Axon type(s)
2. CNS origin/termination
3. Peripheral origin/termination

Answer 4

1. Somatic motor
2. Abducens nucleus
3. Lateral rectus

Question 5

Where do the extrinsic ocular muscles insert?

Answer 5

-Sclera

Question 6

Movements of superior and inferior oblique muscles?

Answer 6

• Superior: Internal rotation (intorsion)

- Inferior: External rotation (extorsion)

Question 7

People with weakness in superior oblique contain of what?

Answer 7

-Double vision

Question 8

What structures are in the cavernous sinus?

Answer 8

• CN’s 3,4,6
• Vi and Vii
• ICA

Question 9

How is levitator palpebrae superioris innervated?

Answer 9

-Bilaterally

Question 10

How is the Superior rectus innervated?

Answer 10

-Contralaterally

Question 11

How is medial rectus, inferior oblique and inferior rectus innervated?

Answer 11

-Ipsilateral

Question 12

Results of CN III injury?

Answer 12

• Ipsilateral eye deviates laterally
• Vertical movement impaired
• Diplopia: double vision
• Ptosis: ipsilateral levator palpebrae superioris is weak
• Mydriasis: ipsilateral pupil is dilated
• Pupil does not constrict in response to light
• Lens cannot be focused for near vision

Question 13

What does CN IV (Trochlear) innervate?

Answer 13

-Contralateral Superior Oblique

Question 14

Why is CN IV unique?

Answer 14

-Only one to originate entirely from a contralateral nucleus and on dorsal brainstem surface

Question 15

What are the results of CN IV injury?

Answer 15

-Patients complain of diplopia when going downstairs or reading

Question 16

Select the true statement:
A) Trochlear deficits lead to a relatively mild deficit
B) Oculomotor nerve injury is associated with a dilated pupil
C) Oculomotor nerve injury is associated with lateral strabismus
D) All the above are true

Answer 16

D

Question 17

Results of CN VI (Abducens) injury (on left side)

Answer 17

• Medial strabismus

* Can look right, but not left. Strabismus also present when looking straight ahead

Question 18

Result of CN VI Nuclear damage?

Answer 18

• Medial strabismus and lateral gaze paralysis
• Ipsilateral eye will not abduct past mid position and contralateral eye will not adduct past mid position.
• Nucleus contains motor neurons and internuclear neurons that ascend in MLF (MLF crosses in midline)

Question 19

What is the function of the Medial Longitudinal Fasciculus?

Answer 19

-It interconnects 3,4, and 6 nuclei to allow coordination of head and eye movement

Question 20

Results of an injury to Medial Longitudinal Fasciculus?

Answer 20

• Internuclear opthalmoplegia
• removes excitatory input to ipsilateral 3 nucleus
• eye ipsilateral to lesion fails to move past mid position during horizontal gaze
• Both CN 6 nuclei are intact lateral movements of both eyes are intact

Question 21

What are the 4 sets of neurons involved in the pupillary light reflex?

Answer 21

1. Afferent limb: (CN II) Retinal ganglion cells to contralateral pretectal nuclei in midbrain
2. Each pretectal nucleus us linked to both EWN, fibers reach the contralateral EWN via posterior commisure
3. Preganglionic parasympathetic fibers enter CN III nerve, synapse in ciliary ganglion
4. Postganglionic fibers in short ciliary nerves enter iris, supply pupillary sphincter

Question 22

What should happen when light is shined into an eye?

Answer 22

-Both eyes should contract. If not, could be a lesion in CN III of midbrain

Question 23

Describe Accommodation.

Answer 23

• To view an object up close, the ciliary muscle must contract, which relaxes lens suspensory ligaments and the lens bulges.
• sphincter pupillae contracts, decreasing light through periphery of lens and forces light thru thick part of lens (center)
• Convergence: both eyes converge due to increased tone in medial rectus muscles

Question 24

Select the true response:
A) The afferent limb of the pupillary reflex is III
B) The efferent limb of the pupillary reflex is IV
C) Accommodation consists of contraction of pupillary sphincter and the ciliary body
D) All the above are true

Answer 24

C

Question 25

Describe the sympathetic pathway to the eye

Answer 25

1. Central fibers from hypothalamus cross midline in midbrain to join ipsilateral descending fibers in pons/medulla 2. Preganglionic fibers emerge from ventral root, travel up sympathetic chain to SCG 3. Postganglionic fibers run with ICA, leave to join Vi in cavernous sinus, then to ciliary nerves

Question 26

Describe the scanning movement.

Answer 26

-Eyes move from one visual target to another very fast, known as saccades

Question 27

Describe the tracking movement.

Answer 27

-AKA smooth pursuit. Eyes follow area of interest across a visual field

Question 28

Describe the compensation movement.

Answer 28

Gaze held on object of interest during head movements, known as vestibuloocular reflex

Question 29

In scanning, where are the gaze centers located?

Answer 29

-Brainstem reticular formation (4)

Question 30

Where is the gaze center for horizontal saccades? Upward? Downward?

Answer 30

1. Horizontal: Paramedian pontine reticular formation (PPRF) each pulls eye to own side 2. Upward: Midbrain, rostral interstitial nuclei of MLF (riMLF) 3. Downward: in midbrain next to upward center

Question 31

What happens during a voluntary saccade to the left?

Answer 31

1. Right frontal eye field activates left PPRF 2. Some PPRF neurons activate adjacent VI neurons (left lateral rectus) 3. Other PPRF neurons send heavily myelinated internuclear fibers in MLF to activate III (right medial rectus)

Question 32

Select the true response: A) Trochlear nerve: Exits brainstem posteriorly B) Oculomotor nerve: Superior oblique muscle C) Abducens nerve: Inferior oblique D) Lateral rectus: Eye adduction E) Inferior rectus: Eye elevation

Answer 32

A

Question 33

``` Select the correct location: A) Edinger- Westphal nucleus: Caudal midbrain B) Oculomotor nucleus: Caudal medulla C) Trochlear nucleus: Rostral midbrain D) Abducens nucleus: Caudal pons E) None of the above are correct ```

Answer 33

D

Question 34

Select correct statement: A) Oculomotor nerve injury results in a mild deficit of eye movement B) Trochlear nerve injury results in a large deficit of eye movement C) Abducens injury results in medial strabismus D) Oculomotor nerve injury results in a constricted pupil due to interruption of sympathetic fibers

Answer 34

C

Question 35

Select correct statement about pupillary reflex: A) Efferent limb is the oculomotor nerve B) Afferent limb is retina ganglion cell fibers in cranial nerve II C) Input from cranial nerve II is sent to the Edinger Westphal nucleus bilaterally D) Postganglionic fibers from the ciliary ganglion innervate the iris and supply the sphincter muscle of the pupil E) All the above are true

Answer 35

E

Question 36

Accommodation includes: A) Contraction of the ciliary muscle to allow the lens to thicken centrally B) Convergence of eyes by slight increase in medial rectus muscle tone bilaterally C) Contraction of sphincter pupillae to constrict pupils D) All the above are part of accommodation

Answer 36

D