Vision Flashcards
what muscles control pupil diameter
dilator pupillae
sphincter pupillae
strength of cornea and lens in diopters?
cornea: 42
len: 20
describe emmetropia
when looking at far objects, lens flattens
when looking at near objects, lens bulges
descrime myopia (short sightedness)
lens too strong, eye too long. lens accommodates by staying flattened.
near vision is fine.
far vision - focsues before retina.
corrected by concave lens
describe hypertropia (far sightedness)
lens too weak, eye too short. lens stays round.
fine for far objects
for near objects, focuses too late
counteracted with convex lens
describe snellen chart
distance viewed/distance a normally sighted person can see the thing at
describe grating acuity test
easy
describe vernier acuity test
easy
describe presbyopia
far sightedness that comes from loss of elasticity of lens, so it stays round (old people)
what are the two types of photoreceptors
rods and cones
describe rods
- high light sensitivity
- single wavelength range: no colour vision
describe cones
- low light sensitivity
- 3 wavelength ranges - blue, green, red
describe phototransduction when there is light
causes conf change in rhodopsin activates g protein turns cGMP to GMP closes Na+ channel hyperpolarisation less glutamate released from photoreceptor
describe phototransduction when there isn’t light
no conf change in rhodopsin
cGMP bound to Na+, so it’s open.
relatively more glutamate is released
two factors affecting acuity
cone density
convergence ratio
describe central retinal (fovea) in terms of cone density and convergence ratio
high cone density/convergence ratio
describe peripheral retina in terms of cone density and convergence ratio
low cone density/convergence ratio
after photoreceptors, where does glutamate go
bipolar cells
are bipolar cells spiking
NO
describe off centre bipolar cells
shining light on centre causes hyperpolarisation - conserves sign of photor’s
ionotropic glutamate gated cation channels
descirbe on centre bipolar cells
shining light in centre causes depolarisation
has metabotropic g protein goupled receptors
are retinal ganglion cells spiking?
yes
do retinal ganglion cells have receptive fields?
yes
describe parasol cells in terms of cell body/dendritic arbour/receptive field size colour sensitivty sensitivity to rapidly changing stimuli which LGN cells they go to
large
not colour sensitive
yes, sensitive
go to magnocellular LGN cells
describe MIDGET cells in terms of cell body/dendritic arbour/receptive field size colour sensitivty sensitivity to rapidly changing stimuli which LGN cells they go to
small
colour sensitive - receptive fields have yellow-blue and red-green opponency
NA
go to parvocellular layers
where is LGN located
thalamus
describe layering
bottom two layers: magnocellular layres
top 4 layers: parvocellular layers
what happens if you put an electrode perpendicularly in to the layers
htey have the same receptive fields
what is PVC aka
area 17, V1, striate cortex
describe PVC simple cells
receptive fields have spatially segregated on/off regions
rotation of bar affects AP rate
monocular
describe PVC complex cells
receptor fields have spatially homogenous on/off regions
rotation of bar affects Ap rate, but location of bar in receptive field doesnt
binocular
describe PVC retinotropic map
adjacent areas of cortex correspond to adjacent areas of visual field
fovea is overrepresented
what are the two main pathways from the PVC to the rest of the brain?
parietal/dorsal/where pathway
temporal/ventral/what pathway
describe how pupillary reflex can be used to determine optic nerve/oculomotor nerve damage
optic nerve damage: no constriction response in either eye
oculomotor nerve damage: no constriction in the damaged side
describe the vestibulo-ocular reflex
sensory: vestibular system
motor: eye movements
- -> since oppostie motor commands need to be generated, inhibition is required.
