Eye Movements

Question 1

What are the four types of eye movements?

Answer 1

1. smooth pursuit
2. saccades
3. reflexes
4. vergence

Question 2

smooth pursuit

Answer 2

tracking

to keep an object on the fovea)

Question 3

saccades

Answer 3

1. rapid, ballistic “jumps” to bring an object onto the fovea
2. There is suppression of visual information during a saccade
3. Why you don’t see a blur of the visual world during a saccade
4. Average of 3 saccades per minute during the day!

Question 4

reflexes

Answer 4

1. neither is monosynaptic
2. VOR: Vestibular ocular reflex (vestibular system)
3. OKN: optokinetic nystagmus (visual object movement)

Question 5

vergence

Answer 5

moving the fovea to an object closer (convergence) or farther away (divergence)

Question 6

Conjugate eye movements:

Answer 6

1. both eyes move in the same direction.

2. Initiated by a variety of sensory inputs, visual and vestibular inputs most important

Question 7

Vergence eye movements:

Answer 7

1. eyes movie in opposite directions

2. Example – both eyes turn nasally (“cross-eyed”) during the near reflex

Question 8

Near reflex:

Answer 8

1. the combination of changes our eyes undergo when we attempt to focus on a near object.
2. Both medial recti contract, pulling the eyes nasally.
3. Pupils constrict to increase the depth of field
4. Ciliary muscles contract, allowing lens to become fatter and thus focus on a near object.

Question 9

near reflex is driven by

Answer 9

visual input to association areas of the visual cortex

Question 10

saccade is a

Answer 10

a rapid movement that brings the eyes to a predetermined target or position at a rate of up to 700˚/second

(contrast to smooth pursuit, which tops out at 50˚/second).

Question 11

Saccades can be used to

Answer 11

1. restore the eye toward the center of orbit during some tracking tasks, whether it was visually or vestibularly evoked.
2. used in voluntary way to rapidly foveate an interesting peripheral stimulus, moving the eye away from the center of orbit.

Question 12

Visually-evoked saccades are ballistic in character

Answer 12

1. Programmed to foveate a particular target, even if the target moves after the saccade is initiated.
2. A very high frequency burst is needed for initial acceleration
3. A carefully calculated steady rate is required to maintain the new eye position

Question 13

Optokinetic nystagmus

Answer 13

Rhythmic pattern of saccades and tracking movements elicited by a simple stimulus like a rotating striped drum

Question 14

Saccades control centers are in the ____

Answer 14

cortex and the superior colliculus.

Question 15

Motor neurons and pattern generators for saccades are located in the ___

Answer 15

midbrain and pons.

Question 16

Vertical saccades –

Answer 16

pattern generator located near the oculomotor nuclei (midbrain)

Question 17

Horizontal saccades –

Answer 17

pattern generator located in the reticular formation near the abducens nucleus
(in the paramedian pontine reticular formation (PPRF))

Question 18

motor neurons for vertical eye movements are in the _____, while motor neurons for horizontal eye movements involve the ______.

Answer 18

oculomotor nucleus

abducens nucleus

Question 19

Horizontal saccades are driven ____

Answer 19

contralaterally

E.g. saccade to the left is driven by activity in the right frontal eye field.

Question 20

The frontal eye field in the frontal lobes of the cortex can activate saccades by two pathways:

Answer 20

1. Direct to the reticular formation

2. Via the superior colliculus and then to the reticular formation

Question 21

Activation of saccades via the superior colliculus has a:

Answer 21

1. retinotopic map AND
2. an auditory spatial map AND
3. a somatotopic map

that are ALL superimposed on a motor map for the movement resulting from the saccade.