Visual Tracts Dr. Dennis Flashcards
What is in the Fibrous layer tunic and describe the parts/layers.
- Sclera dense reg CT type 1 collagen found here and EOM attach here
- Cornea transparent and avascular 5 layers
- Corneal epithelium (nonk strat squam)
- Anterior limiting mem (Bowmans)
- Thick stroma made of keratocytes
- Posterior limiting mem (Descemets)
- Inner endothelium
What is found in the vascular tunic and describe each thing.
- Choroid:
- loose vascularized CT numerous melanocytes
- Bruch membrane is extracell sheet including basal lamina or retinas Pigmented epilthelium
- Ciliary body:
- affects shape of lens
- Iris:
- creates pupil covers outer boundary of lens
What is the retinal tunic?
Inner sensory layer giving rise to optic nerve
- Outer pigmented layer of simple cuboidal epi
- Inner neural layer
jWhat is Limbus?
- Transitional area wehre cornea merges with sclera encircling the cornea
- Epithelial stem cells give rise to progenitor cells moving to corneal epithelium
Functions of the Pigmented epithelium of the retina and what cells make it up?
- Remove free radicals
- Phagocytosis and degradation of waste from photoreceptors
- Isomerize all-trans-retinal to 11-cis-retinal and sends back to photoreceptors
- Forms part of Blood Retina Barrier
- Absorbs scattered light
Made of simple cuboidal or low columnar cells
What are the layers of the retina
- Inner limiting membrane
- Nerve fiber layer with ganglionic cell axons form CN II
- Ganglionic layer with ganglionic cell bodies thick near center not periphery
- Inner plexiform layer with fibers/synapses of ganglion cells and bipolar neurons
- Inner nuclear layer bipolar neurons integrate signals
- Outer plexiform layer conting fiobers and synapses of bipolar neurons and rods/cones
- Outer nuclear layer cell bodies rods cones
- Outer limiting layer holds photoreceptors to mueller cells
- rods and cone layer
- pigmented layer
Describe the inner and outer segments of rods and their function
- Sensitivity to light, allow vision even in low light
- Rhodopsin is in discs
- Inner segment has the glycogen mitochondria and polyribosomes for biosynthetic acvitity
- Outer segment is modifed cilium photosensitive and shaped like short rod with 600-1000 discs
Describe cones and function
- Less numerous and sensitive to light than rods, cones produce color vision in bright light
- Oyter segments are conical, shorter than rods, and discs are continuous invaginations of the plasma membrane
- Iodopsins are found in discs and allows for ROYGBIV to be seen
- (Discs in cones not shed as frequent as rods)
What is the fovea centralis
- High concentration of cones here meaning visual acuity is the sharpest (dops further out you move)
- Absence of vessels cell bodeis and axons of ganglionic and inner nuc layer
What is the macula lutea
- Surrounds the fovea centralils and protects cones
- Has antioxidant properties that filter UV short waves
What is the optic disc
- Blind spot as it is lacking photoreceptors, it only has ganglion cell axons
- located at head of optic nerve
- Ganglion axons from all of the retina converge and dive here
Left half of visual field forms an image on the ___ half of the left retina and the ____ half of the right retina.
Nasal (left)
Temporal (right)
Right half of visual field forms an image on the ___ half of the right retina and the ____ half of the left retina.
nasal (right)
Temporal (left)
What is the purpose of the optic chiasm and what half of the retina crosses?
- Allows for depth perception by bringing together info from areas of both retinas
- The nasal half of each retina crosses contralateral in the optic chiasm
What fibers does the optic tract consist of?
- Fibers from temporal retina (ipsilateral) + fibers from nasal retina (contralateral)
Where does the optic tract terminate and how does it get there?
Terminates in a retinotopic pattern in the Lateral geniculate nucleus and it ravels posteriorly around the cerebral peduncles to get there
Outgoing fibers from the LGN form ____.
Optic radiations
Where does information from the right visual field end up after it has decussated in the optic chiasm?
Left lateral geniculate nucleus
We have the nasal retina of the right eye with right visual field information as well as the left eye temporal retina with right visual field information.
The visual hemifield information ends up in the opposite cortex to what the name is. Left visual hemifield is in the right primary visual cortex
Where is the primary visual cortex located?
On upper and lower banks of the calcarine sulcus
Upper bank of calcarine sulcus, the cuneus receives what information?
- Lower quadrant of contralateral hemifield
The lingual gyrus is the lower bank of the calcarine sulcus, what information does it receive? What is interesting about this?
- Information from the superior quadrant of the contralateral hemifields
- The fibers have to arch rostrally and pass through the temporal lobe and do a broad U turn this is called Meyers loop
The fibers representing the macula and fovea originate where in the LGN, where do they target in the visual cortex, and what is unique about this?
From the central region and they target the most posterior aspect of the occipital pole. It is unique because it represents a disproportionately large volumes in the LGN and PVC compared to its size
How is upper right visual field quadrant represented in the visual cortex?
Lower left quadrant in the visual cortex
contralateral and opposite
Superior colliculus “take home message”?
Important for directing eye movements
retinal imput bypasses the LGN and targets the brachium of the superior colliculus and receives spinotectal and auditory inputs
“Take home message” of the pretectum?
Important in pupillary light reflex
Nuclei is near the midbrain forebrain junction and it receives inputs from optic tract, LGN and suprachiasmatic nucleus
Hemianopia?
- Blindness in one half of visual field
Quadrantanopia?
Loss of vision in a quadrant
Homonymous visual fields?
Conditions in visual field losses are similar in both eyes
Heteronymous visual fields
Visual losses in two eyes are non overlapping, so different regiosn are lost btw the two
What will damage anterior to the chiasm do?
Impacts only the ipsilateral eye as it hasn’t crossed
Damage at the chiasm causes ____
Heteronymous deficits
Damage behind the chiasm causes __
Homonymous deficits
Differentiate between congruous and incongruous
- Congruous is a deficit that can be superimposed upon the other eye, usually the closer a lesion is to the visual cortex the more likely it will be congruous
- Incongruous is when a lesion is in optic tract or radiations, the more anterior it is the more likely it is incongruous
If a lesion is in the right optic nerve before the chiasm, what is the result?
- Incongruent monocular blindness of the right eye
If a lesion is present at the center of the optic chiasm, what is the result?
- The optic chiasm has nasal fibers from both the left and the right eye crossing over.
- Results in bitemporal heteronymous heminanopia
If there is a lesion at the right lateral most part of the optic chiasm what results? (where the X meets on the side)
- Ipsilateral right nasal hemianopia
If there is a lesion in the right optic tract, before the LGN, what results?
Left homonymous hemianopia (left nasal)
Lesion in the right visual cortex?
Left homonymous hemianopia with macular sparing
Inferior temporal optic radiations (meyers loop) lesion in right side
Left superior quadrantanopia
Lesion in the right superior optic radiations?
Left inferior quadrantanopia
What is associative visual agnosia?
- Patient can’t name or describe an object in the visual field, but they can recognize and demonstrate how to use the object.
- Disconnects language from visual cortex due to an infarct of the left occipital lobe and posterior corpus callosum due to PCA damage
