NV - Eye Movement Review - Week 6

Question 1

What is a disadvantage of having front-facing eyes with high acuity?

Answer 1

Slight misalignment will result in diplopia

-the eyes need to be precisely controlled

Question 2

Describe the action of the medial rectus.

Answer 2

Pure adductor

-toward the midline

Question 3

Describe the action of the lateral rectus.

Answer 3

Pure abductor

-away from the midline

Question 4

Describe the three actions of the superior rectus.

Answer 4

Elevation
Intorsion
Adduction
-elevation with increasing abduction

Question 5

Describe the three actions of the inferior rectus.

Answer 5

Depression
Extorsion
Adduction
-depression increases as the eye abducts
-nil when the eye is adducted

Question 6

What muscle is the only depressor in the abducted position?

Answer 6

Inferior rectus

Question 7

Describe the three actions of the superior oblique.

Answer 7

Intorsion
Depression
Abduction
-depression increases as the eye adducts
-nil in abduction

Question 8

What muscle is the only depressor in the adducted position?

Answer 8

Superior oblique

Question 9

Describe the three actions of the inferior oblique.

Answer 9

Extorsion
Elevation
Abduction
-elevation increases with adduction
-nil in abduction

Question 10

What muscle is the only elevator in the adducted position?

Answer 10

Inferior oblique

Question 11

What are the three forms of slow eye movements?

Answer 11

Smooth pursuit
Vestibulo-ocular reflex
Optokinetic nystagmus

Question 12

Why do saccades need to be fast?

Answer 12

Because vision is poor during saccades

• our clearly seen visual world is an illusion
• what are you hiding

Question 13

Briefly describe how a leftward saccade is made, including what is happening before the saccade is made, where impulses are generated, integrated, and what each does.

Answer 13

Omnipause neurons in the PPRF normally inhibit excitatory burst neurons
When no longer dirven sufficiently by fixation cells in the superior colliculus, omnipause neurons become less active
This allows excitatory burst neurons to fire a burst of innervation to the abducens nerve nucleus, vestibular nucleus, and cerebellum
The burst is integrated into a tonic step of innervation
The burst and tonic activity are combined in the abducens nucleus producing a pulse-step
Pulse gets the eye where it needs to quickly
Step keeps it there

Question 14

Keeping in mind how saccades are generated for one eye, how are both eyes moved together? What region of the brain is da?

Answer 14

The saccadic burst originates ipsilaterally to the direction of thr saccade (step produced here as well)
The abducens has interneurons which relay the signal to the contralateral medial rectus muscle via a fibre tract
-medial longitudinal fasiculus

Question 15

For horizontal saccades, where are most of the brain structures responsible located (4)?

Answer 15

Pons and medulla
Midbrain
-3rd nerve nucleus
-superior colliculus

Question 16

What brain structure is additionally involed in downward saccades?

Answer 16

Interstitial nucleus of cajal

Question 17

What is the centre of saccadic action?

Answer 17

Superior colliculus

Question 18

Where do commands to make a saccade come from (2)? What about inhibitory inputs (2)?

Answer 18

Various cortical areas and the retina itself sometimes
Inhibitory from frontal cortex
-striatum
-substantia niagra

Question 19

What part of the brain is responsible for intentional saccade triggering?

Answer 19

FEF

-frontal eye field

Question 20

What part of the brain is responsible for reflexive saccade triggering?

Answer 20

PPC

-posterior parietal complex

Question 21

What part of the brain is responsible for reflexive saccade inhibition?

Answer 21

DLPFC

-dorsolateral prefrontal cortex

Question 22

Is smooth pursuit under voluntary control?

Answer 22

Yes

Question 23

Is the vestibulo-ocular reflex new or ancient? Explain.

Answer 23

Ancient reflex

• 3 neuron arc
• has voluntary overlay

Question 24

What does the vestibulo-ocular reflex compensate for?

Answer 24

Transient head movement

Question 25

What is optokinetic nystagmus? What reflex is it complementary to and why?

Answer 25

Reflexive response to large visual field motion

Continues to operate for constant-velocity stimulus motion, thus complementary to VOR

Question 26

What is the purpose of eye movements during fixation (2)? What is their magnitude?

Answer 26

Tiny subclinical eye movements that serve to prevent image fading and also appear to reflect shifts in attention

Question 27

What are the two roles of the vestibular system?

Answer 27

Maintains balance

Maintains stable gaze as we move in the environment

Question 28

What do semicircular canals sencse? What about the utricle and saccule?

Answer 28

Semicircular - angular acceleration

Utricle/saccule - linear acceleration (including gravity)

Question 29

Describe the three neuron arc of the vestibulo-ocular reflex.

Answer 29

Ears innervated by 8th cranial nerve, projecting to the vesibular nucleus
Vestibular nucleus neurons project to the ocular motor nuclei
Ocular motor nuclei neurons drive the eye

Question 30

What is the dolls head test?

Answer 30

Evaluates the VOR by thrusting the head suddenly and assessing how well the eyes maintain fixation

Question 31

Interaction between what two neuronal pathways can lead to motion sickness and via what?

Answer 31

OKN and vestibular system via the vestibular nuclei

Question 32

What is linearvection/cirularvection?

Answer 32

Feeling of motion despite being stationary

-linear/circular

Question 33

List two stimuli for the vergence system.

Answer 33

Disparity

Blur

Question 34

What is OKN generally integrated with?

Answer 34

Smooth pursuit