Lecture 16 - Occulomotor Systems

Question 1

What are the two main reseaons we move our eyes? [2]

Answer 1

• To look at something

- To track something

Question 2

What are the five types of eye movement? [5]

Answer 2

• Saccades
• Smooth pursuit movements
• Vergence eye movements
• Vestibulo-ocular movements
• Optokinetic movements

Question 3

What are saccades?

Answer 3

Shifting the fovea to a peripheral target

Question 4

What are Smooth pursuit movements?

Answer 4

Keeping the images of a moving target on the fovea

Question 5

What are Vergence eye movements?

Answer 5

Moving the eyes in opposite directions so an image is on both foveae

Question 6

What are Vestibulo-ocular movements?

Answer 6

• Keeps image on retina during brief head movements

- Driven by the vestibular system

Question 7

What are Optokinetic movements?

Answer 7

• Keeps image on fovea during sustained head movements

- Driven by visual stimulation

Question 8

Saccades are very […].

Answer 8

Fast

Question 9

What can we change about a saccade?

Answer 9

• Direction

- Aplitude

Question 10

What direction does Abduction rotate the eye?

Answer 10

Away from the nose

Question 11

Which direction does Adduction rotate the eye?

Answer 11

Towards the nose

Question 12

Which direction does Elevation rotate the eye?

Answer 12

Vetically up

Question 13

Which direction does Depression rotate the eye?

Answer 13

Veritcally down

Question 14

Which direction does Intorsion rotate the eye?

Answer 14

Rotates top of cornea towards the nose

Question 15

Which direction does Extorsion rotate the eye?

Answer 15

Rotates top of cornea away from the nose

Question 16

What are the six muscles that move the eye? [6]

Answer 16

• Superior rectus
• Inferior rectus
• Medial rectus
• Lateral rectus
• Superior oblique
• Inferior oblique

Question 17

Which muscle is responsible for adduction of the eye?

Answer 17

Medial rectus

Question 18

Which muscle is responsible for abduction of the eye?

Answer 18

Lateral rectus

Question 19

What happens to individuals with lesion on extraocular muscles/nerves?

Answer 19

• Suffer double vision

- Image is no longer on the same point of both fovea

Question 20

What are the three cranial nerves that control the extraocular muscles? [3]

Answer 20

• The abducens nerve (CN VI)
• The occulomotor nerve (CN III)
• The trochlear nerve (CN IV)

Question 21

What is the relationship between eye velocity and extraocular motor neuron firing rate?

Answer 21

As the velocity increases the firing rate also increases

Question 22

What happens once the eye has reached its desired position?

Answer 22

It is held in place by contraction of the extraocular muscles

Question 23

Where do the motor circuits for saccades reside?

Answer 23

In the brain stem

Question 24

Where is the horizontal component of a saccade located?

Answer 24

In the pons and meddula

Question 25

Where is the vertical component of the saccade loacted?

Answer 25

In the mesencaphaluc reticular formation (in midbrain)

Question 26

What does the pulse part of the step-pulse signal show?

Answer 26

The speed of the saccade

Question 27

What does the step part of the step-pulse signal show?

Answer 27

The extent of the saccade

Question 28

Whcih neurons give rise to the pulse component?

Answer 28

Burst cells

Question 29

What is the role for medium-lead burst cells?

Answer 29

Making direct conections to the motor neurons

Question 30

What is the role for long-lead burst cells?

Answer 30

• Driving medium-lead burst cells

- Recieving inputs from higher centres

Question 31

What is the role for inhibitory burst cells?

Answer 31

• Supressing contralateral abducens neurons and excitatory burst neurons
• Driven by medium-lead burst cells

Question 32

What is the role for Omnipause cells?

Answer 32

They inhibit burst neurons

Question 33

How do omnipause cells work?

Answer 33

• Fire continuosly

- Stop firing around the time of a saccade

Question 34

Which parts of the brain stem is responsible for maintaining a signal relating to eye position? [2]

Answer 34

• Medial vestibular nucleus

- Nucleus prepositus hypoglossi

Question 35

What are saccades controlled by?

Answer 35

The cerebral cortex

Question 36

What controls the output for the pontine and mescenphalic burst cells?

Answer 36

The superior colliculus

Question 37

What are the two function regions of the superior colliculus? [2]

Answer 37

• Superficial layers

- Intermediate & Deep layers

Question 38

Where do the superficial layers recieve input from?

Answer 38

• Retina

- Primary visual cortex

Question 39

The activity in neurons of the intermediate and deep layers is related to what?

Answer 39

Occulomotor actions

Question 40

What affect do the basal ganglia have on the super colliculus?

Answer 40

They send powerful inhibitory signals

Question 41

What is the role of Frontal eye field neurons?

Answer 41

• They excite movement related neurons in the intermediate layers of the supper colliculus
• Inhibit the inhibitory projection from the basal ganglia

Question 42

Where are the neurons that are responsible for smooth pursuit located? [3]

Answer 42

• The medial vestibular nucleus
• The nucleus prepositus hypoglossi
• The pons

Question 43

Which muscles control vergence?

Answer 43

The horizontal rectus muscles

Question 44

Which neurons control vergence?

Answer 44

Neurons in the occulomotor nucleus of the midbrain