31 - Control of Eye Movements

Question 1

Two components of controlling gaze

Answer 1

1) Oculomotor system:
* Moves the eyes in the orbit (whilst head is still)
* Involves extraocular muscles and neural pathways that coordinate movement of each eye.
2) Head-movement system:
* moves the eye sockets as a whole (whilst head moves).
* Involves vestibular system as well as oculomotor system

Question 2

Saccadic eye movements

Answer 2

Shift fovea rapidly to a new visual target

Question 3

Smooth pursuit eye movements

Answer 3

Keep image of a moving target on the fovea

Question 4

Vergence eye movements

Answer 4

Moves eyes in opposite directions.

EG: When reading a book, looking at something near face

Question 5

Vestibular ocular eye movements

Answer 5

Holds image still on the retina during brief head movements

Question 6

Optokinetic eye movements

Answer 6

Holds the image stationary during sustained head rotation or translation.
EG watching things pass from a moving car/train, etc
Flicking eye movements

Question 7

Five major types of eye movements

Answer 7

1) Saccidic
2) Smooth
3) Vergence
4) Vestibular ocular
5) Optokinetic

Question 8

Where does inferior oblique insert?

Answer 8

Behind equator, just under lateral rectus

Question 9

Eye movements
1
2
3
4
5
6

Answer 9

Up - Elevation
Down - Depression
Abduction - Away from midline
Adduction - To midline
Intortion - Rotating eye to nose
Extortion - Rotating away from nose

Question 10

Superior oblique insertion

Answer 10

Inserts behind equator at an oblique angle close to the medial rectus.

Question 11

Path of superior oblique

Answer 11

Tendon runs through a fibrocartilage pulley or ‘trochlea’

Question 12

Major role of oblique muscles

Answer 12

Torsion

Question 13

Angle of superior rectus insertion to visual axis

Answer 13

~23 degrees

Question 14

*Testing each eye muscle in isolation

Answer 14

EYE MOVEMENTS

Question 15

Testing movements of obliques in isolation.

Answer 15

Superior is looking down towards nose (depression and adduction).
Inferior is looking up towards nose (elevation and adduction).

Question 16

Why is CNVI often affected in disease?

Answer 16

Has a very long path.

Can be affected by things like systemic diabetes, etc.

Question 17

How can both medial rectus muscles be affected?

Answer 17

Internuclear ophthalmoplaegia.

Question 18

Part of brain that controls movement of eyes (conscious)

Answer 18

Frontal eye fields (just in front of the motor cortex)

Question 19

Brain areas involved in coordinating eye movements
1
2

Answer 19

1) Medial longitudinal fasciculus (MLF):
* White matter tract that connects the various cranial nerve nuclei
2) Reticular formation
* Pontine paramedian reticular formation (reticular formation in the pons)
* Mesencephalic paramedian reticular formation (reticular formation in the midbrain)

Question 20

Part of brain involved in coordinating horizontal eye movements

Answer 20

Reticular formation in the pons (coordinate activity of CNVI and CNIII)

Question 21

Part of brain involved in coordinating vertical eye movements

Answer 21

Reticular formation in the midbrain (CN IV and III)

Question 22

Neuronal control of horizontal saccades
1
2

Answer 22

1) Within Pontine Paramedian reticular formation are:
* Burst neurons
- Fire at high frequency just before movement.
- Several types:
* Provide excitatory connections with ispilateral abducens.
* Inhibitory burst neurons suppress the activity of the contralateral abducens
* Omnipause neurons
- Fires continuously EXCEPT during a saccade.
- GABAergic
- Project to contralateral abducens nucleus

Question 23

Control of horizontal saccades
1
2
3

Answer 23

1) Requires simultaneous excitation of burst neurons and inhibition of omnipause neurons
2) Excitatory Burst neurons in abducens nucleus on one side receive input from Cortex.
3) Inhibitory burst neurons from activated abducens nucleus inhibit contralateral abducens nucleus

Communication between nuclei of CNIII and VI

Question 24

Effect of damage to medial longitudinal fasciculus (MLF), EG with MS

Answer 24

Lose control of coordination of horizontal eye movements.

Question 25

Where does the upper motor neuron in horizontal eye saccades originate?

Answer 25

Contralateral frontal eye fields.

Synapses with secondary neuron in superior colliculus

Question 26

Reflex controlling ability to read something while head is moving

Answer 26

Vestibular ocular reflex

Question 27

Role of semicircular canals

Answer 27

Position of head in space (Static)

Question 28

Role of otoliths

Answer 28

Acceleration/deceleration of head

Question 29

Transduction of movement in otolith organs

Answer 29

Cilia arranged in clusters, with tallest cilia on one side, and shortest on opposite side.
Cilia sit within gel, with calcium carbonate on surface.
When head is moved, cilia bend, depolarise cell.

Question 30

Action potentials sent from semicircular canals to brain on turning head

Answer 30

Fluid in horizontal canal will move in one direction, increase firing rate.
Fluid in horizontal canal on opposite side of head will move in opposite direction, and will decrease firing rate

Question 31

Path of information from vestibular system
1
2
3

Answer 31

1) Vestibular information carried by CNVIII (vestibulocochlear nerve) to vestibular nuclei in the medulla (#6).
2) To coordinate head and eye movements information from the vestibular nuclei must be coordinated with the CNIII, CNVI nuclei
3) Connect to medial longitudinal fasciculus

Question 32

*Vestibular ocular reflex

Answer 32

VESTIBULAR OCULAR REFLEX