Visual System

Question 1

What 3 things does the visual system provide?

Answer 1

• sight for the recognition and location of objects
• eye movement control
• information used in postural and limb movement control

Question 2

Where do visual pathways begin?

Answer 2

with cells in the retina that convert light into neural signals

Question 3

Describe the pathways neural signals travel

Answer 3

1) optic nerve
2) optic chiasm
3) optic tract
4) synapses in the lateral geniculate nucleus of the thalamus

Question 4

What type of information does the primary visual cortex process?

Answer 4

It discriminate the shape, size, or texture of objects

Question 5

What is information conveyed to the visual association cortex/secondary visual cortex is analyzed for?

Answer 5

colors and motion

Question 6

What is the action stream used for?

Answer 6

to direct movement

Question 7

What is the perception stream used to recognize?

Answer 7

visual objects

Question 8

the action stream is a stream of visual information that flows ______, whereas the perception stream flows ______.

Answer 8

dorsally

ventrally

Question 9

Normal eye movements require synthesis of information concerning what 4 things?

Answer 9

• Head movements (vestibular information)
• Visual objects (vision information)
• Eye movement and position (proprioceptive information)
• Selection of a visual target (brainstem and cortical areas)

Question 10

The best visual acuity is available on a small region of the retina called the _____.

Answer 10

fovea

Question 11

The exquisite control of eye position that is required to view something as a single object is achieved by what 3 things?

Answer 11

• MLF
• reflexes
• cerebral centers

Question 12

What are the 2 types of eye movements?

Answer 12

• Conjugate

- Vergence

Question 13

Describe conjugate eye movement

Answer 13

both eyes move in the same direction

Question 14

Describe vergence eye movement

Answer 14

eyes move toward the midline or away from the midline (convergence vs. divergence)

Question 15

What are the 2 objectives of eye movements?

Answer 15

• Gaze stabilization

- Direction of gaze

Question 16

Gaze stabilization during head movements is achieved by what 2 reflexes?

Answer 16

• Vestibulo-Ocular Reflex (VOR)

- Optokinetic reflex

Question 17

When is the vestibulo-ocular reflex initiated?

Answer 17

During fast movements of the head

Question 18

When is the optokinetic reflex initiated?

Answer 18

during slow movements of the head

Question 19

Direction of gaze is achieved by what 3 things?

Answer 19

• Saccades
• Smooth pursuits
• Vergence movements

Question 20

What are saccades?

Answer 20

fast eye movements to switch gaze from one object to another

Question 21

Describe an example of a saccadic eye movement

Answer 21

If a person is reading and someone comes into the room, a saccadic eye movement shifts the reader’s gaze from the text to the person.

Question 22

What are smooth pursuit eye movements?

Answer 22

eye movements that follow a moving object

Question 23

What are vergence eye movements?

Answer 23

movement of the eyes toward or away from midline to adjust for different distances between the eyes and the visual target

Question 24

What do VORs stabilize?

Answer 24

visual images during head movements

Question 25

Give an example of how a VOR reflex occurs?

Answer 25

A person attempts to maintain visual fixation of a target while their head turns to the right. The movement of the eyes is matched with the same magnitude and velocity, but in the opposite direction.

Question 26

Describe the pathway a VOR reflex takes starting with rotational acceleration or deceleration of the head

Answer 26

1) rotational acceleration or deceleration of the head 2) receptors in semicircular canals are activated 3) send information to the vestibular nuclei 4) which send info to the oculomotor nuclei 5) which tell the extraocular muscles to respond accordingly

Question 27

The optokinetic reflex adjusts eye position during ____ head movements.

Answer 27

slow

Question 28

Give an example of when the optokinetic reflex is initiated

Answer 28

When a person is walking, the head moves relative to objects in the environment.

Question 29

What elicits an optokinetic reflex?

Answer 29

moving visual stimuli

Question 30

What does the optokinetic reflex allow for?

Answer 30

the eyes to follow large objects in the visual field

Question 31

Cortical centers that influence eye movements include what 3 fields?

Answer 31

- frontal - occipital - temporal

Question 32

What does the frontal eye field provide?

Answer 32

voluntary control of eye movements

Question 33

What do the occipital and temporal eye fields provide?

Answer 33

information for pursuit eye movements

Question 34

What 2 areas of the cortex influence eye movements?

Answer 34

- Posterior parietal cortex | - Dorsolateral prefrontal cortex

Question 35

What does the Posterior parietal cortex provide?

Answer 35

cortical inputs for smooth pursuit movements

Question 36

What does the dorsolateral prefrontal cortex inhibit?

Answer 36

reflexive eye movements as appropriate

Question 37

What 5 things may influence eye movements?

Answer 37

- Auditory information (via the superior colliculus) - VOR - Visual stimuli - Sensory information from extraocular muscles - Limbic system and voluntary control

Question 38

What controls horizontal saccades?

Answer 38

The paramedian pontine reticular formation (PPRF)

Question 39

The paramedian pontine reticular formation (PPRF) controls horizontal saccades via which cranial nerves?

Answer 39

CN III and VI

Question 40

What controls vertical saccades?

Answer 40

The midbrain reticular formation

Question 41

The midbrain reticular formation controls vertical saccades via which cranial nerves?

Answer 41

CN III and IV

Question 42

What controls diagonal saccades?

Answer 42

Adjusting the relative levels of activity of both the PPRF and midbrain reticular formation

Question 43

What kind of eye movements are essential for following a moving object?

Answer 43

Smooth pursuit eye movements

Question 44

What is vection?

Answer 44

the illusion of motion

Question 45

During vection what is inhibited?

Answer 45

activity in the vestibular cortex

Question 46

Activation of the vestibular cortex _____ visual areas of the cortex.

Answer 46

inhibits