W21-L9: Control of Eye movements

Question 1

What are the two systems that stabilize an image of an object on the retina?

Answer 1

Oculomotor and Head-movement system

Question 2

What is the Oculomotor system?

Answer 2

Moves the eyes in the orbit (whilst head is still)`

Involves extraocular muscles and neural pathways that coordinate movement of each eye.

Question 3

What is the Head-movement system?

Answer 3

moves the eye sockets as a whole (whilst head moves).

Involves vestibular system as well as oculomotor system

Question 4

Primary actions of recti

Answer 4

Superior Rectus: Elevation
Inferior Rectus: Depression
Medial rectus: Adduction
Lateral rectus: abduction

Question 5

What is the function of Superior Oblique?

Answer 5

torsion (rotation), adduction and depression

Question 6

What is the function of Inferior Oblique?

Answer 6

torsion, adduction and elevation

Question 7

Why do muscles have multiple actions?

Answer 7

mulitple actions of the muscles on the eyeballs is due to the angle of insertion

Question 8

What is the Medial longitudinal fasciculus?

Answer 8

White matter tract that connects the various cranial nerve nuclei

Question 9

What is the Pontine paramedian reticular formation?

Answer 9

-Horizontal gaze centre
-coordination of MR and
LR of each eye
-coordination of CNIII & CNVI

Question 10

What is the Mesencephalic paramedian reticular formation?

Answer 10

• Vertical gaze centre
• Coordination of SO and SR of each eye
• Coordination of CNIV and CNIII

Question 11

What are the two types of neurones in the Pontine Paramedian reticular formation?

Answer 11

Burst neurones (drive contraction) which fire just before movement and omnipause neurones (inhibit contraction) which work all the time when not contracting

Question 12

What is the neural control of saccades?

Answer 12

1. Excitatory burst neurones receive input from the cortex
2. Stimulates ipsilateral LR via abducens nucleus
3. Via MLF stimulates contralateral CN III nucleus and contralateral MR
4. Inhibitory burst neurones inhibit contralateral abducens via MLF which inhibits contralateral LR
5. Also via MLF ipsilateral CN III nucleus and MR are inhibited

Question 13

Where do frontal eye fields control saccades?

Answer 13

controls saccades in the contralateral direction

Question 14

What do Semicircular canals signal?

Answer 14

Head position

Question 15

What does otolith signal?

Answer 15

Linear acceleration

Question 16

What is the Vestibular-ocular reflex when looking to the left?

Answer 16

Left horiztonal semicircular canal signals to left vestibular nucleus- and then contralateral Nucleus of VI, stimulates LR (of Right eye) and stimulates contralateral (Left) CN III nucleus and MR.

Left vestibular nucleus also stimulates left (ipsilateral) CN III nucleus (MR)