Cranial nerves III, IV, VI

Question 1

What structure separates the motor and sensory nuclei in the spinal cord and in the brainstem?

Answer 1

The sulcus limitans

Question 2

What is the action of the superior rectus muscle?

Answer 2

It elevates the eye- make you look up

Question 3

What is the action of the inferior rectus muscle?

Answer 3

It depresses the eye- makes you look down

Question 4

What is the action of the lateral rectus muscle?

Answer 4

Adbducts the eyeball

Question 5

What is the action of the medial rectus muscle?

Answer 5

It adducts the eyeball

Question 6

What is the action of the superior oblique muscle?

Answer 6

Internal rotation- helps you go cross-eyed- up and in

Question 7

What is the action of the inferior oblique muscle?

Answer 7

External rotation- down and out

Question 8

Where are CN III, IV, and VI located on the brainstem?

Answer 8

III and IV are located in the midbrain and VI is located in the pons

Question 9

Which muscles does the oculomotor nucleus innervate?

Answer 9

Superior, inferior, and medial recti
Inferior oblique
Levator palpebrae superioris

Question 10

Which muscles does the Edigner-Westphal nucleus innervate?

Answer 10

The pupillary sphincter as well as (after a synapse in the parasympathetic ganglion) the ciliary muscle

Question 11

Which muscle does the trochlear and adbucens nuclei innervate respectively?

Answer 11

Trochlear- superior oblique

Lateral rectus- abducens

Question 12

What is the only CN to exit the posterior side of the brainstem?

Answer 12

The trochlear nerve (CN IV)

Question 13

The Edinger-Westphal nucleus is the autonomic component.

Answer 13

Truth.

Question 14

Which CN is the red nucleus closest to?

Answer 14

CN III- oculomotor

Question 15

Let’s talk about the results of a CN III lesion.

Holy crap- there’s a lot (ocho of them)

Answer 15

1. Ipsilateral eye deviates laterally because the medial rectus would be useless and abducens is unopposed.
2. Patient can’t move eye medially.
3. Vertical movement is impaired due to weak superior and inferior recti and inferior oblique
4. Double vision
5. Levator palpebrae superioris is weak so you get a droopy eyelid
6. Mydriasis: the pupil on the affected side is dilated because the pupillary sphincter and ciliary muscle are dysfunctional
7. Pupil doesn’t constrict in response to light
8. Lens cannot be focused for near vision.

Question 16

CN ___ is innervated contralaterally.

Answer 16

CN IV

Question 17

T/F all eyeball related CNs have ipsilateral innervation, except for CN IV?

Answer 17

Trooth. (That’s some appalachan spelling fer ya)

Question 18

T/F- it is a big deal if you’ve got a CN IV lesion?

Answer 18

Not really- the SO muscle moves the eye downwards and laterally, so patients report diplopia (double vision) when going downstairs or reading

Question 19

Because of its long intracranial course, CN ___ is susceptible to increased intracranial pressure.

Answer 19

CN VI

Question 20

Where in the brainstem is CN VI located?

Answer 20

In the caudal pons, the floor of the 4th ventricle

Question 21

CN VI nucleus and the internal genu (of CN VII) together are called:

Answer 21

the facial colliculus.

Question 22

Where do the fibers of CN VI wrap around and turn to exit?

Answer 22

The internal genu of CN VII

Question 23

What is a medial strabismus and what causes it?

Answer 23

It is where the affected eye deviates medially and is caused by a lesion in CN VI

Question 24

Describe the eye movements of someone with a medial strabismus.

Answer 24

Ipsilateral eye will not abduct past the midposition and the contralateral eye will not adduct past the midposition.

Question 25

The medial longitudinal fasciculus does what?

Answer 25

1. Allows the coordination of head and eye movement. | 2. Interconnects CN nuclei III, IV and VI

Question 26

Looking to one side requires what to happen?

Answer 26

The lateral rectus and the contralateral medial rectus to contract simultaneously. MLF allows for this to occur

Question 27

Let's talk casualties. Medial longitudinal fasciculus injuries- what happens? (3 things)

Answer 27

1. Eyeball paralysis due to damage between the nuclei- they can no longer coordinate with each other 2. MLF damage removes the excitatory input to ipsilateral III nucleus (I assume this is the sympathetic functions?) 3. Ipsilateral to the lesion, the eye can't move past the mid point during a moving horizontal gaze

Question 28

If an MLF injury exists, what happens to lateral eye movements (CN VI)?

Answer 28

Nothing- they still work because a median longitudinal fasciculus lesion doesn't damage the CN VI nuclei.

Question 29

What is the pupillary light reflex?

Answer 29

It is the constriction of pupils in response to light.

Question 30

How does the pupillary light reflex work? | 4 stages/4 neurons

Answer 30

1. (afferent limb) The retina receives light and sends the signal to the pretectal nuclei. 2. Each pretectal nucleus is linked to both EWN (Edinger-Westphal Nucleus)- one ipsilaterally and the other one via the posterior commissure. 3. Preganglionic parasympathetic fibers from the EWN enter CN III and synapse in the ciliary ganglion. 4. Postganglionic fibers in the short ciliary nerves enter the iris and supply the pupillary sphincter. 5. Boom. Constriction. In both eyes.

Question 31

The lens of the eye is involved in focusing. At rest the lens is flattened by tension on its capsule exerted by the suspensory ligament. How can you see up close (accommodation)?

Answer 31

The ciliary muscle contracts, which relaxes the suspensory ligaments- this allows the lens to bulge and focus on something close up.

Question 32

What is the near response of accommodation?

Answer 32

It is when the sphincter pupillae contracts- light is decreased through the periphery of the lens. You want to view the object through the thicker part of the middle of the lens instead of the periphery.

Question 33

T/F- there is convergence of the visual axis of both eyes due to increased tone in the lateral rectus?

Answer 33

False- it would be true if we were talking about the medial rectus.

Question 34

What is the sympathetic pathway to the eyes?

Answer 34

Well, I'm not very glad you asked- here we go: (--> means "fibers go to") Central fibers in the hypothalamus --> 1st thoracic vertral nerve root --> Superior cervical ganglion--> CN V--> ciliary nerve.

Question 35

Eyes moving as a pair is known as what type of movements?

Answer 35

Conjugate movements

Question 36

What are the three types of conjugate movements?

Answer 36

1. Scanning- eyes move from one visual target to another in high-speed movement known as saccades 2. Tracking- aka smooth pursuit- eyes follow the area of interest across the visual field 3. Compensation- gaze is held on an object of interest during head movement

Question 37

In the conjugate movements of the eyes, what is compensation also known as?

Answer 37

The vestibulo-ocular reflex

Question 38

How many gaze centers do we have?

Answer 38

4- up, down, left, right

Question 39

Where are the gaze centers located?

Answer 39

In the brainstem reticular formation

Question 40

Specifically, where are the horizontal saccades located?

Answer 40

PPRF (paramedian pontine reticular formation)

Question 41

Specifically, where are the upward saccades located?

Answer 41

In the midbrain- riMLF (rostral interstitial nuclei of the MLF)

Question 42

Specifically, where are the downward saccades located?

Answer 42

In the midbrain next to the upward center

Question 43

Concerning voluntary saccade to the left: Which frontal eye field activates the left PPRF?

Answer 43

The right frontal eye field

Question 44

Concerning voluntary saccade to the left: T/F some PPRF neurons activate adjacent VI neurons

Answer 44

Truth