Visual Systems Norden Flashcards
Purpose of saccades
saccades constantly refresh image to look for changes in environment
optic nerve is composed of what?
retinal ganglion cells
optic nerve is surrounded by what? What layer is continuous with sclera of eye?
dura***, arachnoid, pia
What goes through optic chiasm? What crosses at the optic chiasm?
axons of all RGCs from each eye go through optic chiasm.
Axons from RGCs of the nasal half of both eyes cross to go contralaterally, temporal axons travel ipsilaterally
How does the optic tract course?
optic tract travels posteriorly and courses around the crus cerebri. optic tract ‘hugs’ the interpeduncular fossa
4 main targets of RGCs and function of each?
LGN of Thalamus (form color and movement)
Superior Colliculus (generate eye movements, visual reflexes)
Pretectum of midbrain (pupillary light reflex)
Hypothalamus (circadian rhythm)
location of LGN in thalamus
posterior and lateral
what layers of the LGN receive input from contralateral eye?
Layers 1, 4, and 6
what layers of the LGN receive input from ipsilateral eye?
layers 2, 3, and 5
LGN processes info from what parts of visual field?
processes info from contralateral visual hemifield
how is the binocular portion of vision processed in LGN
given point in the binocular visual field is represented by a column of neurons extending through all 6 layers of the LGN
what is the blood supply to the LGN?
primarily by the anterior choroidal artery (from internal carotid) and branches of the posterior cerebral artery
parvocellular layers of LGN represent which layers and process what information?
Layers 3-6 process color and form vision (central retina)
magnocellular layers of LGN represent which layers and process what information?
Layers 1-2 process information from retinal ganglion cells signaling “movement” (peripheral retina)
LGN neurons project to Area 17 through what tract? (2 names)
geniculo-calcarine tract / optic radiations
optic reactions are part of what subdivision of the internal capsule?
retrolenticular division of the posterior limb of the internal capsule
Axons coming out of the medial part of the LGN pathway
courses dorsally over the lateral ventricle (through parietal lobe) and then in the internal capsule to enter the cuneus gyrus of the calcarine cortex (17)
Axons coming out of the lateral portion of the LGN pathway (Meyer’s Loop)
course rostrally around the temporal horn of the lateral ventricle (through the temporal lobe), then enter the internal capsule to enter the the lingual gyrus of the calcarine cortex ( 17)
Blood supply to the optic radiations?
middle and posterior cerebral arteries
Blood supply to the posterior limb (retrolenticular division) of the internal capsule?
middle cerebral artery
extrastriate visual area definition
other higher-order visual cortical areas in occipital, temporal, and parietal lobes which area 17 projects to
extrastriate areas for ‘where’ and ‘what’ consist of which lobes?
where - occipital and parietal lobes
what - occipital and temporal lobes
RGC to superior colliculus serve what specific function?
play a role in “orienting” to moving stimuli and in directing gaze
cells in the superior colliculus are very sensitive to what?
movement
pulvinar is located where?
nucleus located in dorsal thalamus
pathway of superior colliculus projection to cortex?
RGCs -> Superior Colliculus -> Pulvinar -> Extrastriate Visual Cortex
what type of RGCs project to the hypothalamus and to what nucleus?
primitive light sensitive RGCs that respond to ambient light; suprachiasmatic nucleus of hypothalamus
function of RGC projections to hypothalamus?
linking circadian rhythms/hormonal cycles with ambient illumination; also involved in projections to the reticular formation for regulation of sleep/wake cycles
progressive encephalization definition
processing of visual information in higher order areas of brain
individuals with lesions only in area 17 present with…?
“blindsight” - functionally/cortically blind
individuals can still see light, even though they are not consciously aware of it
individuals with lesions only in occipital lobe present with…?
cortical blindness but deny blindness
visual agnosia is what and occur how?
individual is not blind, but fails to recognize the identity, significance or some other aspect of an object which is seen
occurs from lesions of higher order visual areas with an intact Area 17
object agnosia occurs from?
lesion of area 18, inability to recognize an object on the basis of sight alone
prosopagnosia presentation and cause
inability to match a “face” with an “identity”
bilateral lesion of higher order temporal lobe visual area
only place in the body where blood vessels and CNS tissue can be observed directly
fundus
optic disc location in fundoscopy
nasal (medial) to macula (central retina)
papilledema presentation in fundoscopy and cause
caused by increased ICP
disc is elevated or swollen, darker than normal, or the disc edges are blurred
Why does the disc appear swollen when there is increased intracranial pressure?
pressure is transmitted in the subarachnoid space surrounding the nerve; increased intracranial pressure impedes the return of venous blood from the eye and causes the nerve head to be congested and to appear dark pink
main causes of optic disc swelling not caused by papilledema?
hypertension (bilateral) and optic neuritis
optic neuritis presentation and it is a presenting sign for what condition?
multiple sclerosis
can affect the pupillary light reflex
upon stimulation of the affected eye, the direct reflex will be “sluggish” relative to the direct response of the unaffected eye
relative afferent pupillary defect RAPD (Marcus Gunn pupil)
Shaken Baby Syndrome can lead to death by what?
subdural hematoma
subsequent brain herniation or brainstem avulsion - separation of the brain at the junction of the pons and medulla
signs and symptoms for shaken baby syndrome
- Ecchymosis (bruising) on the sternum
- Presence of retinal hemorrhage (>3 wks age), papilledema, retinal detachment
- A decreased responsiveness
long term consequences of SBS
- Diffuse axonal injury
- Blindness
- Epilepsy, intellectual impairment, etc
