Flashcards in 4.1 Visual Pathways Deck (59):
What do cone cells detect?
Colour and HD
C for colour
What is the fovea?
Dip below the optic disc
What is contained within the fovea?
Highest concentration of cone cells
What is the choroid?
Part of the vascular supply
What does retinal pigment epithelium contain?
What does the retinal pigment epithelium do?
Makes sure you dont have excessive refraction, absorbs some light instead
Why are albinos sensitive to normal levels of light?
Because they lack melanin in their retinal pigment epithelium
Where is the blind spot in the back of the eye and why is it there?
At the optic disc
Because there are no photoreceptor cells
What do horizontal cells do?
Responsible for lateral inhibition
Inhibit bipolar cells activated outside the central field of view
How does light travel once it hits the neural layer of the eye?
Travels through to the photoreceptor cells all the way at the back (bar choroid)
Makes its way back through bipolar cells to the axons of ganglion cells to the optic nerve
What runs alongside the optic nerve as it leaves the eye?
Central artery and vein of the retina
What is the retina?
Light sensitive tissue that lines the back of the eye
Why might an optic disc be swollen?
Due to an increased ICP
What do patients see when their central retinal artery becomes occluded?
What is amaurosis fugax?
Temporary loss of vision
Like a black curtain coming down
How are fibres medial to the retina referred to?
How are fibres lateral to the retina referred to?
Which retinal fibres in the eye decussate?
Do Temporal retinal fibres of the eye decussate, or not?
Where do the nasal retinal fibres decussate?
At the optic chiasm
What kind of retinal fibres does the optic nerve contain?
Contains all the retinal fibres from the SAME (IPSILATERAL) eye
What does the optic tract contain?
ISPILATERAL temporal retinal fibres
CONTRALATEREAL nasal retinal fibres
Where do the optic tracts run to?
Lateral geniculate nucleus
Where is the lateral geniculate nucleus located?
What is the basic function of the lateral geniculate nucleus?
Relay point for the visual fibres to get to the back of the cortex
What structures travel from the lateral geniculate nucleus (thalamus) to the primary visual cortex?
What are the two different types of optic radiations?
Which fibres continue as superior optic radiations once they leave the lateral geniculate nucleus?
Superior nasal and temporal fibres
Where do the superior optic radiations run?
In the parietal lobe
Where do the inferior optic radiations run?
In the temporal lobe
Where do both the superior and inferior radiations end up?
Primary Visual Cortex in the Occipital lobe
How does light hit the retina, if it comes from the medial side?
Hits the lateral (temporal) side
Which retinal fibres are responsible for the nasal visual fields and vice versa?
Temporal fibres for nasal visual fields
Nasal fibre for the temporal visual fields
Which retinal fibres are responsible for the superior visual fields and vice versa?
Inferior retinal fibres for superior fields
Superior retinal fibres for inferior fields
Is a visual field defect referring to the area of visual loss or the site of the lesion?
area of visual loss
How do lesions to the fibres BEFORE the optic chiasm affect the visual fields?
How do lesions to the fibres AT the optic chiasm affect the visual fields?
How do lesions to the fibres AFTER the optic chiasm affect the visual fields?
What kind of visual defect would be cased by an optic nerve lesion?
The entire visual field of one eye is lost
What might cause monocular blindness in children?
What kind of visual defect would be caused by a lesion at the optic chiasm?
BOTH nasal fibres affected
Temporal fields lost
What kind of visual defect would be caused by a lesion at the optic tract?
Which visual field would be affected (relative to the side of the lesion)?
The contralateral side
What the most common cause of a homonymous hemianopia?
(Also neoplasia and trauma)
What are the superior optic radiations responsible for?
Inferior fields of vision
What are the inferior optic radiations responsible for?
Superior fields of vision
If the superior optic radiations had a lesion, what would the visual field defect be?
Contralateral LOWER quadratic anopia
What is the blood supply to the occipital lobe like?
Dual blood supply
Posterior cerebral artery
Middle cerebral artery
Why does macular sparing occurring?
Stroke affecting PCA - most of occipital lobe lost
MCA supplies central part of occipital lobe
Central part of occipital lobe represents macula
Macula vision spared
The afferents of which cranial nerve are stimulated by light?
What is the course of the CN II afferents in the light reflex?
DOES NOT GO TO LGN
Synapses in pretectal area
What do the afferents of CN II synapse to in the light reflex?
Neurones supplying Edinger Westphal nucleus BILATERALLY
What happens after neurones synapse in the Edinger-Westphal nucleus in the light reflex?
BOTH CN IIIs are stimulated
Direct AND consensual pupillary constriction
Which fibres are are stimulated in the Occulomotor nerve in the light reflex?
What is the accommodation reflex required for?
Focus on a near object
What are the three aspects of the accommodation reflex?
What enables convergence in the accommodation reflex?
Medial rectus muscles
What enables pupillary constriction in the accommodation reflex? Why is it needed?
Focus light better
What enables the convexity of the lens in the accommodation reflex? Why is it needed?
Increase refractive power