Visual Tracts Flashcards
What forms the visual pathway?
axons of ganglion cells and the axons of higher order cells on which they synapse
what type of arrangement does the visual pathway maintain at easy relay location?
retinotopic
what are the three layers of the eye?
fibrous layer, vascular layer, retina
what does the fibrous layer of the eye consist of?
the sclera and the cornea
what does the vascular layer of the eye consist of?
choroid, ciliary body, and the iris
what is the role of the sclera?
it is an external layer of the eyeball that protects internal structures and provides sites for muscle insertion
what type of tissue makes up the sclera?
dense regular CT with flat bundles of type I collagen
what are the five distinct layers of the cornea?
corneal epithelium, anterior limiting membrane (bowman membrane), stroma, posterior limiting membrane (descemet’s membrane) and the inner endothelium
what type of tissue makes up the corneal epithelium?
nonkaratinized stratified squamous epithelium
what separates the corneal epithelium from the stroma?
the anterior limiting membrane (Bowman membrane)
what makes up the stroma?
keratocytes
what separates the stroma from the inner endothelium?
the posterior limiting membrane (Descemet’s membrane)
what is the transitional area where the transparent cornea merges with the opaque sclera?
limbus
what does the limbus denote?
the end of Bowman’s area and the beginning of the conjunctiva
what cell population is found at the surface of the limbus and what is their role?
epithelial stem cells- give rise to progenitor cells that move into the corneal epithelium
what is the middle layer of the eye?
the vascular layer
what does the choroid consist of?
loose, well-vascularized connective tissue and melanocytes
what is the role of the melanocytes found in the choroid of the eye?
it prevents light from entering the eye except via the pupil
what is the Bruch’s membrane?
it is a thin extracellular sheet that includes the basal lamina of the retina’s pigmented layer (more anterior membrane)
what is the innermost layer of the eye?
the retina
what are the two layers of the retina?
- outer pigmented layer and 2. inner neural layer
what does the retina develop from?
the optic cup
what is the tissue that makes up the outer pigmented layer of the retina?
simple cuboidal epithelium
what makes up the inner neural layer of the retina?
it is stratified with various neurons and photoreceptors
the neural component of the retina extends to where?
anteriorly to the ora serrata
what are some of the functions of the pigmented epithelium layer of the retina?
it absorbs scattered light, forms part of the blood-retina barrier, isomerizes all-trans-retinal–> 11-cis-retinal, phagocytosis, removes free radicals and secretes ATP
what is the most posterior layer of the retina/ the layer closest to the choroid?
the pigmented epithelium
what are the layers of the neural retina, starting from the most superficial?
inner limiting membrane, nerve fiber layer, ganglionic layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, outer limiting layer, rod and cone layer, pigmented layer
what makes up the inner limiting membrane (layer 1 of the neural retina)?
it is a basement membrane covered by processes of Muller cells
what is contained within the nerve fiber layer (layer 2) of the the neural retina?
ganglionic cell axons
where do the ganglionic cell axons from layer 2 of the neural retina converge and what do they form?
they converge at the optic disc and they form CN II
what does the ganglionic layer (layer 3) of the neural retina contain?
ganglionic cell bodies (thicker near the retina’s center than its periphery
what does the inner plexiform layer (layer 4) of the neural retina contain?
fibers/synapses of ganglionic cells and bipolar neurons
what does the inner nuclear layer (layer 5 of the neural retina) consist of?
bipolar neurons, which integrate signals from rods/cones
what does the outer plexiform layer (layer 6 of the neural retina) contain?
fibers/synapses of bipolar neurons and rods and cones
what does the outer nuclear layer (layer 7 of the neural retina) consist of?
cell bodies of rods and cones
what does the outer limiting layer (layer 8 of the neural retina) consist of?
it is a line of junctional complexes holding photoreceptors to Muller cells
what does the inner segment of rods contain?
glycogen, mitochondria, and polyribosomes for the cells biosynthetic activity
what is the outer segment of rods made up of?
it is modified primary cilium
what protein is found within the discs of rods?
rhodopson
what visual pigment do cones contain?
iodopsin
what is the fovea centralis?
it is the area where visual acuity is the sharpest (highest concentration of cones)
what is the macula lutea?
it surrounds the fovea and protects cones
where is the optic disc located?
at the head of the optic nerve
when does the optic nerve become myelinated?
as it passes through the sclera
how are visual system lesions described?
in terms of their visual field deficits NOT RETINAL FIELDS
the left half of the visual field forms an image where?
upon the nasal (right) half of the left retina and the temporal (right) half of the right retina
the right half of the visual field forms an image where?
upon the nasal (left) half of the right retina and the temporal (left) half of the left retina
what makes up the optic tract?
fibers from the temporal retina (ipsilateral eye) + fibers from nasal retina (contralateral eye)
what is responsible for the depth perception?
the decussation of CN II
where does the optic tract terminate?
in the lateral geniculate nucleus (LGN) of the thalamus
as axons exit the LGN what do they give rise to?
optic radiations, axons that are going to relay the visual information back to the primary visual cortex
ganglionic cell axons that arise in the temporal retina remain what? and terminate where?
they remain uncrossed and terminate in the ipsilateral LGN
axons that arise in the nasal retina do what and terminate where?
they cross and terminate in the contralateral LGN
where does the optic radiation relay its information to?
the primary visual cortex
where is the primary visual cortex located?
on the upper and lower banks of the calcarine sulcus
as fibers leave the LGN, fibers representing the inferior visual field terminate where?
superior to the calcarine sulcus
as fibers leave the LGN, fibers representing the superior visual field do what and terminate where?
they sweep through the temporal loop (meyer’s loop) and terminate inferior to the calcarine sulcus
what is the superior colliculus important for?
directing eye movements
what is the pretectal area important for?
important in pupillary light reflex
what is hemianopia?
blindness in one half of the visual field
what is quadrantanopia?
blindness of a quadrant of the visual field
what is homonymous visual field?
conditions in visual field losses are similar in both eyes
what is heteronymous visual field?
conditions in which the two eyes have non-overlapping field losses
what is macular sparing?
visual field loss that preserves vision in the center of the visual field
how are lesions in the optic tracts and optic radiations described?
congruous or incongruous
what does it mean when a deficit is congruous?
when the visual field loss of one eye can be superimposed on that of the other eye
when does a lesion become more congruous?
the closer a lesion is to the visual cortex
when does a lesion become more incongruous?
the more anterior a lesion is in the optic tract or radiations
damage anterior to the chiasm affects what?
only the ipsilateral eye
damage to the chiasm causes what?
heteronymous deficits
damage behind the chiasm causes what?
homonymous deficits
what is associative visual agnosia?
infarction of the left occipital lobe and posterior corpus callosum
what is associative visual agnosia typically due to?
PCA damage
associative visual agnosia is a disconnection between what?
the language area from the visual association cortex
what is the classical presentation of associative visual agnosia?
the patient cannot name or describe an object in the visual field but he can recognize and demonstrate its use
