Lecture 11 - Superior colliculus, pulvinar (LA)

Question 1

Pupil constriction is mediated by light via symp or para?

Answer 1

Para

Question 2

Dilation is mediated by the absence of light via symp or para?

Answer 2

Symp

Question 3

What is the accessory optic system?

Answer 3

The primary visual system in fish and birds

Question 4

Superior colliculus

Answer 4

A key area for the orienting response, directing gaze quickly to a novel stimulus (touch, sound, etc.)

Question 5

Pulvinar (part of thalamus)

Answer 5

May be involved in allocation of attention, role of visual stimulation, sensitive to emotion or relay between different cortical areas

Question 6

Not all axons leaving retina go to LGN - some also branch earlier to? Para or symp?

Answer 6

Pretectal nucleus in the midbrain -> projects bilaterally to Edinger-Westphal nuclei -> motor innervation to the pupillary sphincter (part of para - chollinergic)

Question 7

Are the pretechtal and Edinger-Westphal nucleus in or near the 3rd nerve nuclei?

Answer 7

Near - this means that damage to the 3rd nerve nuclei will not affect pupillary constriction

Question 8

What is important about the bilaterality of the pretectal nucleus projection to the Edinger-Westphal nuclei?

Answer 8

It means that shining a light into either eye causes both pupils to constrict

Question 9

What is the “near triad”?

Answer 9

When looking at things near us, there is a synergistic interrelationship between: 1) Pupillary constriction (better focus from “pinhole” effect of smaller pupil) 2) Lens accommodation (thicker lens) 3) Convergence of the two eyes (to keep image on corresponding points of both retina) Of the fibres reaching the cillary ganglion, most (by a 30:1 ratio) go to the cillary muscles of the lens, so that when the pupil constricts, the lens accommodates.

Question 10

Does “near triad” occur in blind people?

Answer 10

Yes - using finger as a target to give yourself a sense of “near

Question 11

What makes the pupil dilate?

Answer 11

-Innervation to the sphincter is inhibited so this muscle relaxes -Dilator muscles are excited via symp NS (hypothalamus)

Question 12

What is Horner’s syndrome?

Answer 12

Congenital or acquired condition where there is disruption to the pupillary circuit responsible for dilation of the pupils -Lose dilation (so results in contraction) -Lid droops -Sweating disrupted (dry face in hot room) -Blood vessels dilate in the region innervated by this nerve chain (flushed face)

Question 13

How does lung cancer result in Horner’s syndrome?

Answer 13

As the neuron for the dilator pupillary circuit goes above the apex of the lung - tumours on the apex would disrupt this circuit

Question 14

In congenital Horner’s syndrome, why does the affected eye have less pigment (is lighter) than the other?

Answer 14

During development, symp NS is important for the distribution of pigment in the iris - disrupt this and one eye will have less pigment. However, this is innocuous.

Question 15

3 things pupil is driven by?

Answer 15

Light, sense of near, psychological arousal

Question 16

Two areas in accessory optic system that is like to mammals?

Answer 16

Visual Wuist (analogous to PVC) Pretectum

Question 17

What stimuli do the directionally-selective neurones of the AOS prefer?

Answer 17

Large ans slow-moving - it is part of the circuitry for optokinetic nystagmus and visual-vestibular interaction, both of which involve motion of much or all of the visual field

*Nystagmus refers to rapid involuntary movements that may cause one or both eyes to move from side to side, up and down or around in circles.

Question 18

Differences b/n Optokinetic and Vestibular system?

Answer 18

OPTO

• Visually driven
• Responds to low freq
• Sustained responses

VEST

• Driven by acceleration of semicircular canals
• Responds to high freq
• Transient responses

Question 19

How separate are the geniculocortical and AOS pathways? How do responses vary across mammalian species then? (Cats, monkeys, humans)

Answer 19

In mammals- they’re not, they converge. This means that OKN (optokinetics) is generated from both direct input to the AOS as well as input coming back from visual cortical areas.

CATS- NOT (nucleus of the optic tract) gets both retinal and cortical inputs BUT retina dominates

MONKEYS- NOT gets both, cortex dominates

HUMANS- NOT gets both, cortex GREATLY dominates

Moral? Old CNS don’t disappear- they just get more deeply embedded in new structures

Question 20

Superior colliculus is bigger/smaller in humans compared to birds?

Answer 20

Smaller

Question 21

In birds, the colliculus has projections that resemble?

Answer 21

Primary dorsal and ventral systems- so evolution moved these functions from midbrain to cortex in primates

Question 22

SC role in mammals - rather than for conscious vision, its more focused on?

Answer 22

Gaze control- moving our eye

Question 23

Why do we move our eyes?

Answer 23

Take snapshots and our brain integrates this so we think we see clearly- other animals like birds can just move their heads hence gaze control in not important

Question 24

Where does SC receive inhibitory input from?

Answer 24

Basal ganglia (striatum- sub nigra) from the frontal cortex

Question 25

How are SC motor cells organised?

Answer 25

Retinotopically

Question 26

What gets the eyes moving/orient gaze quickly?

Answer 26

Retina -> SC -> Brainstem
(motor centres)
This is for short latency responses (fast responses) - BUT still need longer term responses mediated by genicular cortical pathways (the ones we use for conscious vision) as the direct, faster pathway doesn’t say anything about WHAT the stimulus is.

Question 27

What receptive fields overlap in SC?

Answer 27

3 senses (auditory, visual, somatosensory)- makes integration across the sense modalities possible

Allows for tactile responses as these nonvisual inputs to the SC make possible for accurate saccades to nonvisual stimuli and allow for the non-visual enhancement of response to a multisensory stimulus
eg. something lands on my arm, I can look at it

Question 28

T/F: There is redundancy in mammals as when SC is damaged, FEF can take over

Answer 28

T

Question 29

How does the FEF (Frontal eye fields) get the eyes to move on its own if the SC is damaged?

Answer 29

Through the direct FEF -> reticular formation pathway

* Only makes long responses but not the short express saccades that the colliculus is involved with

Question 30

When inhibitory input from basal ganglia is affected, what happens?

Answer 30

People lose the ability to inhibit unwanted gaze

Question 31

Where does the pulvinar receive input from? Where does it project to?

Answer 31

Both layers of SC and projects widely to the various visual cortical areas and parietal cortex

Question 32

Where is the pulvinar located?

Answer 32

On top of the SC

Question 33

T/F: Pulvinar only has retinotopic areas

Answer 33

F- has both non-ret and ret

Question 34

Lesions of the pulvinar (esp. medial) can impair?

Answer 34

Facial emotion processing

Question 35

Pulvinar nucles of the thalamus is able to?

Answer 35

1) Integrate visual activity across cortical areas
2) help develop a salience map across the visual field
3) Aid in processing of emotionally sig stimuli