light and the eye Flashcards
cornea
clear outer tissue
bends light wave
pupil
light wave sent through
a hole in iris
iris
muscle that controls size of pupil
contracts and relaxes
lens
light hits lens
bends rays and focuses them on retina
retina
light sensitive tissue lining back of eye
accommodation
process by which eye maintains clear image on retina
muscles change shape of lens
muscles tighten causing lens to thicken
focus on closer objects
ciliary muscles
increase focusing power by increasing curvature of lens
contract or relax
light adaptation
sensory adaptation to different levels of light
near point
distance at which lens cannot adjust any further for close objects
presbyopia
hardening of lens
weakening of ciliary muscles
distance of near point increases with age
hyperopia
farsightedness
myopia
nearsightedness
cant see distant objects clearly
causes differences in eye shape
refractive myopia
cornea or lens bends too much light
axial myopia
eyeball to long
cone cells
detect colour
operate in normal daylight conditions
focus on fine detail
larger but fewer
concentrated on fovea
rod cells
more sensitive in low light
black and white
more numerous in peripheral
on retina, not fovea
distribution of rods and cones
cones densely packed in fovea
rods distributed on retina
blind spot
contains no receptors
where optical nerve meets eye
not noticed as brain fills in space
synaptic terminal
where electrical signal propagates
passed onto visual neurons
inner segments
cellular structures such as ribosomes and mitochondria
outer segments
contain light sensitive visual pigments
where light is transduced into energy
components of rods and cones
opsin
large protein that crosses disc membrane
retinal
light sensitive molecule within disc
isomerisatin
process in which retinal changes its shape due to the absorption of light
= transduction
occurs when retinal absorbs light
spatial summation
simultaneous signals coming from multiple pre synaptic neuron’s received by one postsynaptic neuron
added together to reach threshold
temporal summation
single presynaptic neuron rapid firing signals to postsynaptic neuron
added together to reach threshold
light sensitivity in rod cells
individually rods require less light to respond
convergence of rod activity on ganglion increases likelihood of firing
allows spatial summation
cannot resolve fine detail
visual acuity in cone cells
one to one wiring with ganglion cells
provides information to brain about spatial position
can see fine detail
need more light to respond to cause respond than rods
