Kenyon: Eye Movements

Question 1

The external muscles of the eye are controlled by lower motor neurons in what 3 brainstem nuclei?

Answer 1

3, 4, 6

Question 2

What do eye movements accomplish?

Answer 2

they move the eye so that a point of interest is focused on the fovea

Question 3

What’s intortion? What’s extorsion?

Answer 3

medial rotation (top towards nose)
lateral rotation (top away from nose)

Question 4

What actions does the superior oblique have?

Answer 4

depression; intorsion

Question 5

What actions does the inferior oblique have?

Answer 5

elevation; extorsion

Question 6

Where does the superior oblique muscle attach? What does contraction of the superior oblique do to the eye?

Answer 6

at the back of the eyeball;

depresses the eye and rotates it

Question 7

The effect of the superior oblique muscle varies with the direction of the eye. Which ABDUCTION, contraction of the superior oblique does more (blank). With ADDUCTION, contraction of the superior oblique does more (blank)

Answer 7

intorsion; depression

Question 8

The muscles of the eye are (blank) muscles. They have (blank) in brainstem nuclei and (blank) in brainstem and cortex.

Answer 8

lower motor neurons; upper motor neurons

Question 9

1 motor neuron in the eye activates (blank) muscle fibers

Answer 9

3

Question 10

What components does CN 3 have to the eye muscles?

Answer 10

somatic muscles of eyelid

autonomic to pupil

Question 11

The nerve contains axons to contralateral superior oblique only

Answer 11

CN 4

Question 12

Motor neurons to ipsilateral lateral rectus only

Answer 12

CN 6

Question 13

What is unique about CN 4 and its exit from the brainstem?

Answer 13

exits the DORSAL surface of the brainstem, and then crosses over to the contralateral side

Question 14

What is clinically significant about the CN 4 nuclei?

Answer 14

they are close together; a lesion does not have to be large to affect both of them!

Question 15

What will paralysis of the superior oblique muscle result in? How will the patient compensate for the loss?

Answer 15

diplopia on looking downward; tilt head toward the weak muscle

Question 16

Does CN 6 cross over?

Answer 16

no; remains on ipsilateral side

Question 17

Most common palsy due to the long course of the nerve

Answer 17

loss of CN 6

Question 18

What will damage to CN 6 result in? How do patients compensate?

Answer 18

loss of lateral rectus; so eye will fail to abduct on lateral gaze and can intort causing double vision; compensate by rotation of the head

Question 19

Does CN 3 cross over?

Answer 19

no

Question 20

What happens to the eye when there is damage to CN 3?

Answer 20

eye will go down and out

*due to unopposed action of SO and LR muscles

Question 21

Neurons in the oculomotor nucleus also innervate the (blank) muscles of the eyelid.

Answer 21

levator

Question 22

CN 3 also carries axons from (blank) that drive pupillary constriction

Answer 22

Edinger-Westphal nucleus

Question 23

With damage to CN 3, ptosis occurs. Why? How can you compensate?

Answer 23

loss of levator palpebrae superioris; compensate by contracting frontalis muscle

Question 24

What is the near reflex triad to test CN 3?

Answer 24

vergence adduction of eyeballs
accomodation of the lens
pupillary constriction

Question 25

Rapid ballistic* movements that put an image on the fovea

Answer 25

saccades

Question 26

Slow tracking movements to keep an image on the fovea

Answer 26

smooth pursuit

Question 27

Align the fovea with targets at different distances (tracking something moving toward or away from you) Move the eyes in opposite directions (conjugate movements) so that the image is positioned on both foveas.

Answer 27

vergence

Question 28

Compensate for movements of the head - driven by the vestibular system Hold images stable during brief head movements

Answer 28

vestibulo-ocular movements

Question 29

When is the VOR reflex most important?

Answer 29

during acceleration or rapid rotation

Question 30

Each semicircular canal transmits a tonic signal to the vestibular nerve even when the eyes are still. A pathological imbalance in the signals from the vestibular system will result in (blank) when the head is still.

Answer 30

nystagmus

Question 31

Rapid ballistic movements (figure) that fix on a target and continue afterwards - voluntary or reflexive Shift the fovea rapidly to a target spotted at the periphery The system figures out where the eye will point and snaps it to that position. This is not tracking.

Answer 31

saccades

Question 32

Are saccades voluntary or reflexive?

Answer 32

can be either * voluntary: reading * involuntary: tomato

Question 33

The (blank) controlling the eye muscles are located in CN 3, 4, and 6 nuclei. They receive input from (blank) in two gaze centers in the reticular formation that control the saccade.

Answer 33

lower motor neurons; | upper motor neurons

Question 34

The (blank) of the reticular formation generates all kinds of horizontal movements including saccades

Answer 34

horizontal gaze center

Question 35

The (blank) of the reticular formation generates all kinds of vertical movements including saccades

Answer 35

vertical gaze center

Question 36

Why are there two kinds of neurons in the abducens nucleus? What are they?

Answer 36

abducens nucleus must send motor neurons to the lateral rectus on the ipsilateral side, and internuclear neurons across the MLF to the contralateral nucleus of 3 to activate the medial rectus

Question 37

So, nucleus of 6 sends (blank) to lateral rectus, and (blank) to PPRF and ultimately the medial rectus

Answer 37

lower motor neurons; upper motor neurons

Question 38

In addition to exciting the contralateral nucleus of 3, what do neurons in the PPRF do?

Answer 38

they drive inhibitory interneurons to the contralateral abducens nucleus to inhibit the opposing rectus muscles

Question 39

Saccades are ballistic. Where are the targeting calculations done?

Answer 39

upper motor neurons in two higher structures * superior colliculus * frontal eye field

Question 40

T/F: The saccade is to put a specific point in the visual field onto the fovea, not to move the eye a specific amount

Answer 40

True *monkey experiment Train a monkey to make a saccade, and then shift the eye to a further location, and the monkey will still look at the intended target

Question 41

What do upper motor neruons in the frontal eye field and the superior colliculus do?

Answer 41

command saccades

Question 42

What do upper motor neurons in the occipital and parietal lobes do?

Answer 42

command other movements

Question 43

What do upper motor neurons in the cortex, frontal eye fields, and superior colliculus signal to?

Answer 43

upper motor neurons in the vertical and horizontal gaze centers

Question 44

Where do upper motor neurons in the vertical and horizontal gaze centers signal to?

Answer 44

lower motor neurons *CN 3, 4, 6

Question 45

Smooth pursuit movements are driven through the (blank)

Answer 45

horizontal gaze center

Question 46

What areas provide sensory information that is essential for initiation and guidance of smooth pursuit movements?

Answer 46

visual areas in the parietal and occipital lobes

Question 47

Our eyes are moving all around all the time. Therefore, the images sent to the visual centers are constantly changing. Q: How can we make sense out of that information?

Answer 47

The visual centers also know about the commands moving the eye and use this information to construct a stable image