20 (pt 1) Visual System Flashcards
pupillary light reflex afferents
CN II
pupillary light reflex efferents
CN II
optic nerve lesion
ipsilateral blindness
optic chiasm lesion
bitemporal hemianopsia
optic tract lesion
contralateral homonymous hemianopsia
Meyers loop lesion
contralateral superior homonymous quandrantinopia
visual cortex lesion
contralateral homonymous hemianopsia with macular sparring
oculomotor nerve lesion
ipsilateral
“Down and out” gaze
Ptosis
Dilated, non-reactive pupil
Double vision (diplopia)
pupil
opening where light enters the eye
iris
colored portion of eye
sclera
white of eye
-attachment of extra ocular muscles
cornea
external surface of eye
eye refraction
conductive
membrane that folds back from the inside of the eyelid and attaches to the sclera
immune response
where does the optic nerve receive visual information from?
retina
three laters of the eye from outside to inside
sclera/cornea
choroid/ciliary body
retina
phototransduction
conversion of light into electrical signals
-occurs in the retina
lens
lens focuses light onto fovea
forms sharp images of near objects
accommodation: changing of shape of lensf
fovea
-has highest visual acuity
-smallest visual field
-seeing clearly in bright light
what type of photoreceptor cells does the fovea contain?
cone receptors → color
optic disc
blind spot
vitreous humor
jelly-like liquid located posteriorly that keeps the shape of the eyeball
aqueous humor
jelly-like liquid located anteriorly that moistens the cornea
superior oblique
- intorsion: down/in
- depresses eye when adducted
inferior oblique
- extorsion: up/in
- elevates eye when adducted
photoreceptors
only light sensitive cells in the retina
rods: black/white, low light vision, high light sensitivity
cones: color, low light sensitivity
what type of potentials do photoreceptors have?
graded potentials
flow of information in the retina
Light→Photoreceptors→Bipolar Cells
↓ ↑
Horizontal Cell Amacrine Cells
Bipolar Cells → Ganglion Cells → Brain (via optic nerve)
ganglion cells
only source of output from the retina to the optic nerve
what type of potentials do ganglion cells fire?
action potentials
pigment epithelium of retina
contains melanin to decrease backscattering of light and prevent blurring of images
inner neuronal layer of retina
three neuron chain responsible for phototransduction:
-bipolar cells
-horizontal cells
-amacrine cells
interneurons of the retina
horizontal cells
amacrine cells
superior optic radiation
inferior visual field
inferior optic radiation
superior visual field
primary visual cortex
discriminates shape, size, texture
primary visual cortex “homunculus”
Central vision (fovea): Posterior portion (near the occipital pole)
Peripheral vision: Anterior (deeper into the calcarine sulcus)
Upper visual field: Below the calcarine sulcus (lingual gyrus)
Lower visual field: Above the calcarine sulcus (cuneus gyrus)
dorsal/action stream
Pareto-occipital cortex
information used to direct movement
ventral/perception stream
occipito-temporal cortex
information used to recognize visual objects
visual versus retinal field
Visual field The external space you see (left/right)
Retinal field The internal surface of the retina that receives the light
how do retinal fields work
visual image is inverted and reversed when projected onto retina
ex:
- inferior retina sees superior visual field
-nasal retina sees temporal visual field
2 functional categories of eye movement
stabilize gaze: VOR and optokinetic reflex
directing gaze: saccades/smooth pursuit
VOR
keeps image of object at same place on retina
optokinetic reflex
use of visual info to stabilize images during slow head movements
- train example
saccades
ballistic, rapid eye movements
- reading
smooth pursuit
slower tracking movement of eyes
-keep moving object on retina
conjugate eye movements
both eyes move in same direction
vergence eye movements
convergence: both eyes move towards midline when target moves from far to near
divergence: both eyes move away from midline to shift gaze to distant object
gaze centers in the reticular formation
paramedian pontine: horizontal gaze center
rostral interstitial nucleus: vertical gaze center
medial longitudinal fasciculus
synchronizes eye movements by coordinating activations of gaze centers
forebrain control of eye movements
initiating and accurately shifting eyes toward targets
frontal eye field
contralateral saccades and smooth pursuit
Parieto-occipital-temporal cortex
ipsilateral smooth pursuit
superior colliculus (optic tectum)
accuracy, frequency, and velocity of saccades
