Lecture 7 - Cranial Nerves III, IV, VI

Question 1

Sensory and motor nuclei are separated in the brainstem by the _____ _____.

Answer 1

sulcus limitans

Question 2

Cranial nerve nuclei are often _____ in the brainstem.

Answer 2

discontinuous

Question 3

The oculomotor nerve (CN III) has a sympathetic _______ nuclei and the parasympathetic _____-______ nucleus. The trochlear nerve (CN IV) has the _______ nucleus, and the abducens nerve (CN VI) has the ______ nucleus.

Answer 3

• oculomotor
• Edinger-Westphal
• trochlear
• abducens

Question 4

The superior rectus ______ the eye, while the inferior rectus ______ the eye.

Answer 4

• elevates

- depresses

Question 5

The lateral rectus ______ the eye, while the medial rectus _______ the eye.

Answer 5

• abducts

- adducts

Question 6

The superior oblique causes ______ ______, while the inferior oblique causes ______ ______.

Answer 6

• internal rotation (intorsion)

- external rotation (extorsion)

Question 7

Which 4 cranial nerves innervate the eye/surrounding muscles?

Answer 7

• optic (CN II)
• oculomotor (CN III)
• trochlear (CN IV)
• abducens (CN VI)

Question 8

The oculomotor nerve (CN III) is easily seen in XS of the _____ ______. The trochlear nerve (CN IV) is easily seen in XS of the ______ _______. The abducens nerve is easily seen in XS of the ______ ______.

Answer 8

• rostral midbrain
• caudal midbrain
• caudal pons

Question 9

The Edinger-Westphal nucleus starts in the ______ ______, and supplies the preganglionic fibers to the ______ ganglion. Postganglionic fibers laterally wrap around the eye to innervate the ______ sphincter and the ______ muscle.

Answer 9

• rostral midbrain
• ciliary
• pupillary
• ciliary

Question 10

The oculomotor nucleus supplies the voluntary _____ of the eye. It goes _____ and _____ to the eye.

Answer 10

• muscles
• superior
• inferior

Question 11

The ____ ____ _____ muscle of elevation for the eyelid is innervated [bilaterally/contralaterally] by the oculomotor nerve (CN III). The _____ _____ muscle, which elevates the eye, is innerated [bilaterally/contralaterally].

Answer 11

• levator palpebrae superioris
• bilaterally
• superior rectus
• contralaterally

Question 12

The oculomotor nucleus supplies the medial rectus, inferior rectus, and inferior oblique [bilaterally/ipsilaterally]. The Edinger-Westphal nucleus innervates the ciliary ganglia [bilaterally/ipsilaterally].

Answer 12

• ipsilaterally

- ipsilaterally

Question 13

Within the brainstem, the oculomotor and Edinger-Westphal nuclei are very close, so a lesion affects ______ motor outputs. Lesions outside the brainstem affect the eyes _______, because the fibers for each eye are separate.

Answer 13

• both

- ipsilaterally (only same side affected)

Question 14

Outside the brainstem, an oculomotor lesion causing ipsilateral deviation of an eye is called _____ _____. Deviation is lateral, because the medial rectus is weakened; eyes can’t be moved ______.

Answer 14

• lateral strabismus

- medially

Question 15

4 internal muscles weakened by oculomotor nucleus/nerve injury.

Answer 15

• medial rectus
• superior rectus
• inferior rectus
• inferior oblique

Question 16

An oculomotor nerve injury causing double vision is called _______. Ipsilateral levator palpebrae superioris weakness is called ______. If the pupil does not dilate on one side in response to light, it is called ______.

Answer 16

• diplopia
• ptosis
• mydriasis

Question 17

The trochlear nucleus is in the periaqueductal gray (PAG), posterolateral to the ______ ______ _______.

Answer 17

medial longitudinal fasciculus

Question 18

The trochlear nerve is unique of the cranial nerves, because it is the only one to entirely originate from a _______ nucleus, and is the only nerve on the ______ brainstem surface.

Answer 18

• contralateral

- dorsal

Question 19

The trochlear nerve innervates the _____ ______ muscle. Trochlear fibers leave the nucleus and turn caudally in PAG, arch dorsally to _______, then leave the brainstem in the _____ - _____ junction

Answer 19

• superior oblique
• decussate
• midbrain - pons

Question 20

Trochlear lesions have less noticeable deficits, since only the ______ _____ muscle is affected, moving the eyes down and laterally. The result of lesions here is ______.

Answer 20

• superior oblique

- diplopia (double vision)

Question 21

Due to the long, inferior intracranial course of the ______ nerve, it is susceptible to increased intracranial pressure.

Answer 21

abducens

Question 22

The abducens innervates the [contralateral/ipsilateral] _____ _____ muscle, which ______ the eye.

Answer 22

• ipsilateral
• lateral rectus
• abducts (ABDUCens - ABDUCt)

Question 23

The abducens nucleus is located in the floor of the ___ ventricle in the _____ ____.

Answer 23

• 4th

- caudal pons

Question 24

Located medial to the abducens nucleus are the _____ ____ _____ and motor fibers of the ______ nerve.

Answer 24

• medial longitudinal fasciculus (MLF)

- facial (CN VII)

Question 25

Fibers of the trochlear nerve wrap around the internal _____ of the facial nerve (CN VII). This part and the trochlear nucleus form the ______ ______. The nucleus contains motor neurons and internuclear neurons that ascend up the ______ ______ ______.

Answer 25

- genu - facial colliculus - medial longitudinal fasciculus

Question 26

Injury to the abducens nerves causes ipsilateral _____ ______ and ______ _______ paralysis.

Answer 26

- medial strabismus | - lateral gaze

Question 27

The medial longitudinal fasciculus is located on the _____ aspect of the brainstem.

Answer 27

posterior

Question 28

If the abducens nucleus is injured, the ipsilateral eye will not ______ past midposition, and the contralateral eye will not ______ past midposition.

Answer 28

- abduct | - adduct

Question 29

Both eyes work together for lateral gaze. The ipsilateral eye requires the ______ rectus, while the contralateral eye requires the ______ rectus to contract simultaneously.

Answer 29

- lateral | - medial

Question 30

The medial longitudinal fasciculus (MLF) allows coordination of _____ and _____ movement. The MLF interconnects cranial nerves ___, ___, and ___ to allow this.

Answer 30

- head - eye - CN III - CN IV - CN VI

Question 31

Damage to the MLF causes "paralysis of the eye due to damage between the nuclei" called _______ ________.

Answer 31

internuclear ophthalmoplegia

Question 32

MLF damage removes excitatory input to ipsilateral _____ nucleus. Consequently, the eye ipsilateral to the lesion fails to move past midposition during _____ ____. Both ______ nuclei are intact, so lateral movements of both eyes are intact.

Answer 32

- oculomotor - horizontal gaze - abducens

Question 33

The pupillary light reflex involves 4 sets of neurons: 1. ______ _____: retinal ganglion to pretectal nuclei 2. Pretectal nuclei to ______-_____ nuclei via the posterior commissure 3. Preganglionic parasympathetic into _______ nerve, synapse in ciliary ganglion 4. Postganglionic fibers in short ciliary nerves enter iris and supply the ______ __ ______

Answer 33

- afferent limb - Edinger-Westphal - oculomotor - sphincter of pupillae

Question 34

Changes in optical power by the eye by modifying curvature of the lens in response to objects at varying distances is called ________.

Answer 34

accommodation

Question 35

At _____, the lens is flattened by tension on its capsule from the suspensory ligament. For _____ vision, the ciliary muscles contract, relaxing the lens suspensory ligaments. This causes the lens to _______ bulge.

Answer 35

- rest - near - passively

Question 36

When the pupillary sphincter contracts, _____ light enters the lens of the eye. As muscle tone changes through accommodation, closer objects cause the eyes to move together as the object nears the face, a process called ________.

Answer 36

- less | - convergence

Question 37

The process of receiving a visual stimulus and responding to it with ocular muscles is as follows: 1. Receive signal from ________ and direct it to ipsilateral fibers of midbrain and pons 2. Receive signals in preganglionic fibers of first _____ ventral nerve root. These then ascend the sympathetic chain to the _____ _______ ganglion. 3. Postganglionic fibers ascend with the ______ _____ arteries 4. Join cranial nerve ____, enter _____ nerves

Answer 37

1. hypothalamus 2. thoracic; superior cervical 3. internal carotid 4. VI (abducens); ciliary

Question 38

The eyes move as pairs. This is called _____ movement, of which there are 3 types: 1. _______: eyes move from between targets with high speed motions called saccades 2. _______: eyes follow a moving target through space 3. _______: eyes stay on target of interest while the head moves. This movement involves the vestibular system, and is called the ________ reflex

Answer 38

- conjugate - scanning - tracking - compensation - vestibulocular

Question 39

Scanning involves ______ ______ in the reticular formation. There are 4 of these, which have the movements, "left, right, up, down." 1 & 2. _______ ______: paramedian pontine reticular formation (PPRF), each pulls eye to its own side 3. _______ ______: midbrain, rostral interstitial nuclei of the MLF (riMLF) 4. _______ ______: in midbrain, next to upward center

Answer 39

- gaze centers - horizontal saccades - upward saccades - downward saccades

Question 40

Saccade (rapid scanning eye movement) to the Left: 1. RIGHT eye field activates ______ paramedian pontine reticular formation (PPRF) 2. PPRF then activates adjacent _______ neurons 3. PPRF also signal MLF to activate the ______ nerve that supplies the medial rectus Result: simultaneous contraction from BOTH rectus muscles (due to 2 dif cranial nerves used) results in saccade to the left

Answer 40

1. left 2. abducens (CN VI) 3. oculomotor (CN III)