topic 6 the eye Flashcards
(26 cards)
what are the light receptors in the eye called?
photoreceptors
what does the cornea do?
transparent lens that refracts light as it enters the eye
what does the iris do?
controls the amount of light entering the pupil using muscles
what does the lens do?
transparent disc that changes shape to focus light onto the retina
what does the retina do?
contains light receptor cells- rods and cones
what does the optic nerve do?
is a sensory neuron which sends impulses from the retina to the brain
what does the pupil do?
hole that allows light to enter the eye
where is the blind spot?
where the optic nerve leaves the eye and there are no photoreceptor cells, so it is not sensitive to light
what is the fovea?
part of the retina with lots of photoreceptors
what pigment does a rod cell contain?
rhodopsin
what pigment does a cone cell contain?
iodopsin
what does a breakdown in pigment cause?
a generator potential
when does rhodopsin breakdown?
in dim light
when does iodopsin breakdown?
in bright light
are rod cells or cone cells more sensitive?
rod
how are rod cells sensitive to light?
distinguish between light and dark under dim light
not colour images
how are cone cells less sensitive to light?
senstitive to different wavelengths of light
red sensitive/blue sensitive/green sensitive
combined effect means light of all wavelengths can be observed
what is sensitivity?
the amount of light required to stimulate the receptor
what is visual acuity?
the ability to distinguish between 2 different points of light
how does the brain form an image?
receptors are hit by light so are stimulated
sends impulses to the brain
interpret impulse pattern as an image
how are rods/cones connected to the brain?
synapses connect rods/cones to bipolar neurons
connect to ganglion cells via synapses
these have axons, which extend to the optic nerve, which connects to the brain
why do rod cells have low visual acuity?
multiple connect to single bipolar cells
brain cannot interpret which impulses are sent by specific rods
only one impulse is sent
brain only gets a general understanding of vision being light or dark
why do cone cells have high visual acuity?
single cone cell is connected to a single bipolar cell
brain can interpret different spots of light
receives information about colour detected and where light is
knows which bipolar cell connects to which cone cell
how does summation occur in rod cells?
single rod cell stimulated unlikely to provide a large enough generator potential to stimulate nerve impulses
when a group is stimulated, combined generator potentials are enough to reach the threshold
stimulates bipolar cell to conduct nerve impulses towards the optic nerve
summation allows sight in dimmer light
