Lecture 11- Extrageniculate visual pathways (LA) Flashcards
Pupil constriction is mediated by light via symp or para?
Para
Dilation is mediated by the absence of light via symp or para?
Symp
What is the accessory optic system?
The primary visual system in fish and birds
Superior colliculus
A key area for the orienting response, directing gaze quickly to a novel stimulus (touch, sound, etc.)
Pulvinar (part of thalamus)
May be involved in allocation of attention, role of visual stimulation, sensitive to emotion or relay between different cortical areas
Not all axons leaving retina go to LGN - some also branch earlier to? Para or symp?
Pretectal nucleus in the midbrain -> projects bilaterally to Edinger-Westphal nuclei -> motor innervation to the pupillary sphincter (part of para - chollinergic)
Are the pretechtal and Edinger-Westphal nucleus in or near the 3rd nerve nuclei?
Near - this means that damage to the 3rd nerve nuclei will not affect pupillary constriction
What is important about the bilaterality of the pretectal nucleus projection to the Edinger-Westphal nuclei?
It means that shining a light into either eye causes both pupils to constrict
What is the “near triad”?
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.
Does “near triad” occur in blind people?
Yes - using finger as a target to give yourself a sense of “near
What makes the pupil dilate?
What makes the pupil dilate?
-Innervation to the sphincter is inhibited so this muscle relaxes -Dilator muscles are excited via symp NS (hypothalamus)
What is Horner’s syndrome?
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)
How does lung cancer result in Horner’s syndrome?
As the neuron for the dilator pupillary circuit goes above the apex of the lung - tumours on the apex would disrupt this circuit
In congenital Horner’s syndrome, why does the affected eye have less pigment (is lighter) than the other?
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.
3 things pupil is driven by?
Light, sense of near, psychological arousal
