3. The Eye Flashcards
UV Photoreceptors in birds
Courtship
Males have UV feathers which a female can see due to their photoreceptors
UV Photoreceptors in birds
Foraging
Waxy surfaces of fruits have UV light that birds can see with their photoreceptors
UV Photoreceptors in birds
Prey identification
Rodents discharge reflects UV light which birds can see giving them a trail to the rodent
Photoreceptors in the eye
Cones
Rods
Predators have binocular vision
Each eye overlaps at the front creating a single 3D image
Eyes at the front of the head
Better depth perception
Prey have monocular vision
Each eye works separately with little overlapping
Eyes positioned on the side for wider field of vision, good for detecting predators
Poorer depth perception
Owl
Visual field: 110
Elongated so can’t rotate in the sockets, turn their head instead
Large number of rod cells wide range of pupil size, helps them hunt in low light
Sheep
Visual field: 270
Located high in the skull, better vision when grazing
Rectangular pupils increase the accuracy of depth perception
Cornea
Description: transparent covering on the eye
Purpose: protection of the eye
Retina
Description: layer of photoreceptors at the back of the eye
Purpose: detecting light rays that are focused by the cornea and lens
Choroid
Description: layer of blood vessels with a black pigment
Purpose: nourishing the eye and absorbing light
Cilliary body
Description: attached to the underside of the lens
Purpose: helps with focusing by altering the shape of the lens
Pupil
Description: hole in the middle of the iris
Purpose: allowing light to enter the eye
Lens
Description: transparent, flexible and can change shape due to the cilliary body
Purpose: focuses light onto the retina and focuses objects
Iris
Description: ring of muscles around the pupil
Purpose: provides eye with the colour, controls the amount of light that enters the eye
Fovea
Description: spot located on the macula, has a high density of cone cells
Purpose: sharp central vision, light is focused into this spot by the lens
Optic disc
Description: blind spot where there are no photoreceptors
Purpose: where the optic nerve leaves the eye
Optic nerve
Description: bundle of fibres
Purpose: relaying information from the retina to fovea to the brain
How does the eye work?
Light enters the eye through the cornea and lens
Muscles in the iris contract/relax to control how much light enters
Lens focuses the light
Projects light to the retina
Photoreceptors in the retina covert light energy to electrical signals
Signals sent to the brain
Structure of the retina
Inner neutral layer
Contains photoreceptors, bipolar neurons and ganglion cells
Structure of the retina
Outer pigmented
Helps absorb light
Cones
Higher intensity than rods
Allows us to see colour
High level of visual sharpness
Each cone is connected to optic nerve
Rods
Light sensitive and functions in the dark
Can’t detect colour
Many rod cells share a connection with optic nerve
