9.2.8 - The eye Flashcards
What does the cornea do?
Plays a part in focussing light and protecting the eye.
What does the iris do?
Controls the amount of light entering the eye.
What do suspensory ligaments do?
Can relax and contract to alter the thickness of the lens.
What is the sclera?
The tough white membrane on outside of the eye.
Where are rod cells and cone cells found?
Rod cells - on the retina around the fovea.
Cone cells - in the fovea
How many rod and cone cells connect to 1 bipolar neuron?
1 cone cell
Multiple rod cells
What is retinal convergence in rod cells?
Multiple rod cells are connected to one bipolar neuron so it’s much more likely that the threshold value for a generator potential will be reached by summation.
What must happen for a generator potential to be produced in rod cells?
The pigment rhodopsin must be broken down.
What light intensity is able to break rhodopsin down in rod cells?
low light intensity.
Why do rod cells have low visual acuity (distinguishing between 2 objects)
Light received by different rod cells will only generate one impulse.
Therefore the brain cannot distinguish between separate sources of light.
What 2 things are bipolar neurone connected to?
Either a rod or cone cell and a sensory neuron.
Where are cone cells found?
Fovea
Why can cone cells only respond to high light intensities ?
summation cannot occur son larger intensity is needed to reach threshold.
What is the pigment in cone cells called?
Iodopsin
What type of light intensity is required to break down iodopsin?
Higher light intensity.
What makes up rhodopsin?
retinal
opsin
How does rhodopsin work?
When a photon of light hits the rhodopsin, retinal converts from cis to trans form.
This changes the shape of the retinal and puts strain on the bonding between opsin and retinal, breaking up the molecule.
this is bleaching
describe how a generator potential can be produced by a rod cell?
When rhodopsin is bleached, this causes the Na ion channels to close, making it less permeable to sodium.
However, the sodium pump continues to work and so sodium ions are removed from the cell.
This makes the inside of the rod cell more negative than normal.
This hyperpolarisation is known as the ‘generator potential’.
what is bleaching?
when rhodopsin is broken.
Explain the role of rhodopsin in the generation of a nerve impulse in the bipolar neuron when light falls on the retina.
rhodopsin breaks down in to opsin and retinal.
causing sodium channels to become blocked.
This leads to the rod cell hyper polarising as the Na-K pump continues to remove sodium ions.
Describe the role of rod cells in initiating action potentials to the brain of the mouse.
Rhodopsin forms retinal and opsin.
Na ion channels close
Sodium-potassium pump continues
Hyperpolarisation inside rod cells
release of neurotransmitter stops.
Action potential in sensory neuron.
What is glutamate?
An inhibitory neurotransmitter that is released by rod cells.
Describe how light causes a change in the release of glutamate from rod cells.
Rhodopsin is bleached to form opsin and retinal.
This causes Na ion channels to close.
Sodium ions still move out via the sodium potassium pump so rod cells become hyper polarised.
This stops the release of glutamate.
