Homeostasis and Response - THE EYE Flashcards
The structure of the eye changes according to the light intensity…
which is referred to as the iris reflex.
As light hits the eye, the first structure that it meets is the…
cornea.
The cornea is completely….
transparent to allow the light to pass through, and so has no blood vessels.
This means that all the oxygen that it needs has to diffuse into it from the outside air, rather than be supplied from the blood.
The cornea needs to be tough enough to maintain the shape of the eye and is a protective layer.
The light is “refracted,” or redirected by the cornea, in such a manner that the rays are focused into a precise image on the retina.
The iris is the coloured part of the eye which controls how…
big or small the pupil is.
The iris is coloured because…
The function of the iris is to limit the amount of light that passes through the lens to the retina. To make the iris opaque, it is coated with the pigment melanin, in varying degrees for each of us.
The pupil is simply a gap in the middle of the eye that allows light to pass through to the…
lens.
The lens needs to…
refract the light. The lens can change its shape which allows it to control how much and to what degree it refracts the light, ensuring that the image reflected onto the retina is perfectly focused.
The retina is made up of two different types of receptor cells…
- Cone cells - sensitive to the colour of light (don’t work well in low light intensity)
- Rod cells allow you to see in the dark and are more sensitive than cone cells but cannot distinguish colours.
The Fovea is a region of the retina made up of only cone cells and the eye wants to focus light on this point so that…
we can always see clearly.
Optic Nerve transmits impulses generated by the…
receptor cells to the brain.
The iris reflex ensures that the perfect amount of light is refracted onto the retina in different…
light intensities.
In high light intensity…
damage can be caused to the retina so the iris contracts, preventing too much light from passing through the pupil.
In low light intensity, the iris…
relaxes so that more light can pass through to the lens and you can see more.
CONSTRICTED PUPIL AND
DILATED PUPIL
To control the iris reflex process the iris is made up of two different types of muscle:
- Inside - circular muscles - that stretch around the pupil like circles
- Radial muscles
