The Eye Flashcards
List the structure of the eye we need to know
- The pupil
- The lens
- Iris
- Blind spot
- Fovea
- Retina
- Optic nerve
What is the function of the pupil in the eye?
Where light enters the eye
What is the function of the iris in the eye?
Controls how much light enters the eye
What is the function of the fovea in the eye?
Area of retina containing many photoreceptor cells - mostly cones
What is the function of the retina in the eye?
Full of photoreceptor cells to detect light
What is the optic nerve?
Bundle of nerves that carries nerve impulses from the retina to the brain
What is the blind spot?
- Area of the eye with the retina photoreceptors
- Where optic nerve leaves eye
Label an eye diagram
See notes
How do the photoreceptors in eye conduct impulses to the brain? 6
- Light is focused onto retina by lens
- Absorbed by pigments in the photoreceptors
- Causes some sodium ion channels to open
- If threshold is reached an action potential is generated
- Carried through bipolar neurone to optic nerve
- Takes impulses to the brain
What are the 2 types of photoreceptor?
- Rods
- Cones
List the properties of the rod cells 4
- Monochromatic [one pigment: black/white]
- Low visual acuity
- More sensitive to low light
- 3 rods to one bipolar neurone
Where are rod cells mostly found?
Peripheral part of retina
Where are cone cells mostly found?
Concentrated in the fovea
List the properties of cone cells 4
- High visual acuity
- Trichromatic [three pigments]
- 1 cone to each bipolar neurone
- Less sensitive to low light
What optical pigments do cone cells detect?
- Red pigment
- Green pigment
- Blue pigment
How are different colours seen?
Different proportions of optical pigments are stimulated
How do pupils react to low light? 5
- Photoreceptor detects low light
- Transmits impulses along sensory neurone to CNS
- CNS via relay neurone to radial muscles in iris
- Radial muscles contract
- Pupils dilate
How do pupils react to bright light? 5
- Photoreceptor detects bright light
- Transmits impulses along sensory neurone to CNS
- CNS via relay neurone to circular muscles in iris
- Circular muscles contract
- Pupils contract
How is pupil dilation/contraction an example of a reflex?
- It’s fast
- It’s unconsciously done
Explain what happens to rod cells in the dark. 13
- Steady flow of Na+ ions into outer segment
- Through open cation channels
- Through the cell surface membrane
- At the same time CSM actively pumps Na+ out of cell
- Active transport needs ATP from mitochondria in inner segment
- Concentration gradient maintained between inner and outer segment
- Na+ ions flow down
- Depolarises cell slightly
- Potential difference across is -40mV
- Cell releases glutamate neurotransmitter across synapse
- Binds to bipolar cell and stops depolarisation
- Stops cation channels in bipolar cell opening so no Na+ enters
- No action potential generated in optic nerve synapsing with bipolar cell
Explain what happens to rod cells in the light 12
- Light on the retina causes rhodopsin to break down by bleaching
- Into trans-retinal and opsin
- Opsin catalyses a series of membrane bound reactions
- Closing the cation channels in the outer segment
- Influx of Na+ ions blocked
- Inner segment actively pumps out Na+
- Interior of cell is more negative causing hyperpolarisation
- Neurotransmitter glutamate not released across synapse
- Depolarisation occurs in bipolar cell
- Because cation channels are still open
- Action potential generated in optic nerve
- Transmitted to visual cortex of the brain
What must occur for the rod cell to be restimulated in the light?
Rhodopsin must be reformed
How is rhodopsin reformed? 3
- ATP from the mitochondria in the inner segment
- Converts trans-retinal back into cis-retinal
- Rejoins to opsin and rhodopsin is reformed
