Section 12.2 - Photoreception (Eye) Flashcards
What is the Sclera?
The outer white, tough fibrous layer of the eyeball.
Function of the Sclera
- maintains the eye shape
- acts as a protective layer
What is the Cornea?
At the front, the sclera becomes clear and is known as the cornea.
Function of the Cornea
- It bends light towards the pupil, light enter eye.
- focuses light through bending or refraction
-protect front of eye
What is the Aqueous Humour?
Clear, watery fluid located behind the cornea.
Function of the Aquarius Humour?
- The fluid maintains the shape of the cornea, and provides oxygen and nutrients for surrounding cells.
What is the Choroid?
The middle layer of the eyeball, it’s thin and dark.
Function of the Choroid
- absorbs stray light rays that are not detected by photoreceptors.
- contains blood vessels that supply the retina.
Iris
Toward the front the choroid forms the iris.
Function of the Iris
Regulates the amount of light that enters the eye.
- adjusts size of pupil based on light conditions (adaptation).
What is the Pupil?
The Iris contains the pupil
Function of the pupil?
- opening for light to pass through.
What is the Retina?
Internal layer of the eye, forms the back of the eye.
What does the Retina contain?
Photoreceptor cells that capture light and generate neural messages.
Examples of photoreceptors
Rods and Cones in the retina
Rods
- Detect black, white, grey
- More sensitive than cones
- Dim light, night vision
Where are the rods SPECIFICALLY located?
They’re located around the edges of the retina, provide peripheral vision.
Cones
- Colour vision: red, blue, green.
- sensitive to different colours
Where are the Cones SPECIFICALLY located
- packed at centre of retina, in an area called FOVEA CENTRALIS.
What are the Ciliary Muscles?
- behind the Iris
- the choroid thickens and forms the ciliary muscles, which surround the lens.
Function of the Ciliary Muscles
Changes shape of the lens in order to focus.
Function of the Lens
Bend and Focus light rays on the retina, specifically onto the fovea centralis.
Optic Nerve
The rods and cones send sensory impulses to the brain via the optic nerve.
What’s is the Vitreous Humour
Fluid that fills the eyeball, surrounded by retina.
Function of the Vitreous Humour
- Jelly-like fluid that maintains the shape of the eyeball.
- Allows light to pass through inner eye
Blind Spot
Region at the back of the inner eye, where no photoreceptors are found.
Suspensory Ligaments
Strings that attach the ciliary muscles to the lens.
What does the Cornea look like?
Transparent layer, allows light to pass through.
What does the Sclera look like?
The sclera is the opaque, visible white portion of one’s eye.
Accommodation
Is adjustments to the shape of the lens.
What controls the lens shape?
- the ciliary muscles
How does the eye accommodate to see distant objects?
- ciliary muscles relax,
- sensory ligaments stretched
- lens flatter
- more concave
How does the eye accommodate to see closer objects?
- lens becomes round, fatter, more convex.
- ciliary muscles contract
-suspensory ligaments relax.
Cataracts
Occur when a lens becomes cloudy, preventing light from passing through to the retina.
- most likely occur as people age
Astigmatism
Occurs when the surface of the lens or cornea does not have a smooth curve.
- vision is blurred
Glaucoma
Damage to the retina caused by excessive pressure from build up of aqueous humour in eye,
- causes blindness.
Nearsightedness (myopia)
Unable to see distant objects.
- eyeball too long, lens too round.
- image focused in front of retina
- corrected by using concave lens
Farsightedness (hyperopia)
Unable to see near object.
- eyeball too short, lens too flat.
- focused behind retina
- corrected with convex lens.
Pathway of Light
Cornea,
Pupil,
lens,
vitreous humour,
retina,
optic nerve,
optic chiasma,
and finally to visual cortex in occipital love.
CPLVROV
What do rods and cones contain?
Photopigments - absorb light
What are photopigments composed of?
A membrane protein called OPSIN, and the light absorbing chromosphere retinal.
What’s the photo pigment in rods called?
Rhodopsin
What happens when light strikes a photopigment?
The structure of retina is altered and becomes partially detached from the opsin protein.
OPSIN then undergoes a conformational change leading to a series of biochemical reactions
When are photoreceptor Na+ channels open?
In the dark.
Neurotransmitter (glutamate) is released from photoreceptors in the dark.
Glutamate = inhibitory neurotransmitter
(No action potential)
