The eye Ch 52 Flashcards
Central Neurophysiology of Vision
Visual pathway
Nasal halves:
Optic nerves –>cross at optic chiasm–>optic tract
Temporal retinas: Optic nerve–>optic chiasm (don’t cross)–>optic tract
Fibers of optic tract synapse in
dorsal lateral geniculate nucleus (thalmus)
Visual fibers pass to (4)
- suprachiasmatic nucleus of hypothalmus
- Pretectal nuclei in midbrain
- Superior colliculus
- Ventral lateral geniculate nucleus of thalmus
Suprachiasmatic nuclus of hypothalmus responsible for
circadian rhythms
Pretectal nuclei in midbrain responsible for
reflex movement of eye
Superior colliculus responsible for
eye movement
Ventral lateral geniculate nucleus of thalamus responsible for
body behavior
Layers of dorsal lateral geniculate nucleus
half come from one eye, half from the other
dorsal lateral geniculate nucleus role
gate transmission of signals, controls how much of signal passes to cortex
Magnocellular layers input comes from
type M ganglion cells
(rapid conduction, black and white)
Lizard brain
Parvocellular layers get input from
type P ganglion cells
(transmit color, convey accuracy, moderate conduction velocity)
Visual cortex location
calcarine fissure area, terminus of visual signals
Primary visual cortex has ___ layers
6 layers
M retinal ganglion cells terminate
in Ivcalpha
P ganglion cells terminate in
layer Iva and Ivcbeta
color blobs role
activated by color signals, thought to decipher color
Two pathways for analysis of visual information
- 3-D position, gross forms and motion of objects
- Analysis of visual detail and color
Perimetry
measures blindess in portions of the retina
Scotomata
blind spots outside of optic disk
Retinitis pigmentosa
portions of retina degenerate and lead to excessive melanin deposits
Lesion on optic nerve yields
blindness
lesion bitemporal hemainopsia
interruption of optic chiasm prevents crossing of impulses = half blindess
Lesion homonyous hemianpsia
interruption of an optic tract results in the loss of nervet in the corressponding half of retina
same side lesion, niether eye can see objects to opposite side of head
Neural pathway for vision
CN III
CN IV
CN VI
How many eye muscles are there
3 pairs (6 total)
Voluntary fixation movements
person chooses to find object to focus on
involuntary fixation movements
holds eye firmly once it has been found
Three types of eye movements
- Flicking
- Slow drift
- continuous tremor
Saccadic movement of eye
continually moving visual scene - eye fixes on one object after another
i.e. reading, driving
Pursuit movement
Eyes remain fixed on moving object
Superior colliculi role
turning towards a visual disturbance
(also involves somatic and acoustic signals)
Fusion of the visual image
if two images are not “in register” interference excitation signals oculomotor apparatus
Stereopsis
Detects distances of visual objects up to 200 feet
Depth perception is determined by
pathways activated - different ones register based on how far away object of focus is
Strabismus
squint or cross eye, lack of fusion in one or more visual coordinates
fix: patch or surgery
Accommodation clues - what triggers them?
changing distance of focus leads to clues for accomodation
Accommodation - what else helps accomodation?
Pupillary diameter
changing distance leads to the following clues for accomodation:
- Chromatic abberration - the eye can determine which color ray is better in focus
- convergence
- Clarity of focus in depth of fovea vs edges
- Degree of accommodation oscillates - visual image becomes clearer when oscillation of lens strength changes in proper direction
Horners syndrome:
interruption of sympathetic nerve fibers to pupillary dilator muscle
pupil remains constricted in one ye and eyelid droops, blood vessels remain dilated
