photoreceptors in the eyes Flashcards
(29 cards)
What does the retina contain?
Photoreceptor cells
What are the types of photoreceptor cells?
Rods and cones
What is the fovea?
The centre of vision
Where is the blind spot?
A break in the retina where the optic nerve connects
Where are there the most cones?
In the fovea
Where are there the most rods?
In the peripheral
What are rods useful for?
Vision at low light intensities
What are cones useful for?
Good discrimination of vision
What is visual sensitivity?
The ability to see at low light intensities
Which photoreceptor has a higher visual sensitivity?
Rods
What are the reasons for this?
They contain rhodopsin, several rods synapse with one bipolar neurone
What is rhodopsin?
Pigment in rods which allows them to see low light intensities
Why are many rods on one bipolar neurone useful in dim lights?
It allows for spatial summation so the threshold value can be reached
Why do cones have a low visual sensitivity?
They only have one cone synapsed to a bipolar neurone, so no spatial summation occurs
Where is poorest vision in dim lights?
Fovea
What is acuity?
The ability to discriminate detail
Which photoreceptor has a high visual acuity?
Cones
Why is this?
One cone synapses with one bipolar neurone so there are several sets of impulses so there’s no blurring
Where is acuity the greatest?
The fovea
Why is this?
There are the most cone cells
Why do rods have a low visual acuity?
They share a bipolar neurone, so the brain only gets one set of impulses for many rods
What are the three types of cones?
Red, green and blue sensitive cones
How do they absorb light?
Corresponding to wavelengths of each specific colour
What is the pigment in each cone?
Iodopsin
