Photoreceptors Flashcards
Where are the rods and cones found?
the retina
What are rods?
cells which cannot distinguish between the different wavelengths of light and processes images in black and white
Why can rods detect light at very low intensities?
retinal convergence- many rod cells connect to one sensory neurone
what is the protein pigment found in rod cells?
rhodopsin
What does light cause to happen in the rod cells?
break down of rhodopsin
What cells link rod cells to the sensory neurone?
bipolar cells
Why can the threshold be met at low light intensities?
- rhodopsin can be broken down at low light intensities
- many rod cells are connected to one bipolar cell, so spatial summation occurs (collectively it is a big enough stimuli)
What is a disadvantage of retinal convergence?
less accurate vision at low intensities, as the brain cannot distinguish between the different light sources
What is meant by the term low visual acuity
two light sources close together cannot be seen as separate
What are the three iodopsin pigments found in the different type of cone cells?
red, green and blue
What is different about the 3 types of cone cells?
ca all absorb different wavelengths of light
What allows us to see colour images?
the varying proportions of light absorbed by cone cells
Why is a more light needed to stimulate a response in cone cells?
- iodopsin is only broken down in high light intensities/requires more light energy to be broken down
- no retinal convergence or spatial summation(one cone cell connected to one bipolar cell)
What is an advantage of not having retinal convergence in cone cells?
high visual acuity
Describe the distribution of rods and cones
uneven
What is the fovea?
the point where the lens focuses most light, therefore the point receiving the highest light intensity
Why are most cone cells located near the fovea?
as it is the area with the highest light intensity and cone cells require high light intensities to respond
Why are rod cells further away from the fovea?
as they only need lower light intensities to respond
What is the blind spot?
an area of the retina with no photoreceptors, so no light can be detected
How do muscles in the eye work together to narrow the pupil?
- circular contracts
- radial relaxes
How does a fovea with a large density of cone cells allow animals to see objects in detail?
- high visual acuity
- one cone cell connected to single neurone
- separate impulses sent to the brain
