Photoreceptors: Rod + Cone Cells Flashcards
Where are the light receptors of the eye found?
The light receptors on the eye are found on the retina
What are two main types of photoreceptors?
The two main type of photoreceptors are rod cells and cone cells
⇒Outline features of rod cells (4pts)
1* quantity of rod cells compared to cone cells
2* rod cells are connected to?
3* rod cells see in colour/black & white
4* light intensities
5* visual acuity level
1* there are more rod cells than cone cells
2* many rod cells will be connected to a single sensory neuron in the optic nerve
3* only images in black/white can be seen
4* light at low intensities can be detected
5* low visual acuity level
What do both rod cells and cone cells act like?
Rod cells and cone cells both act as transducers by converting light energy into the electrical energy of a nerve impulse
Why can rod cells only see images in black and white?
Rod cells cannot distinguish between different wavelengths of light therefore images only in black and white can be seen
Why can rod cells detect light at low intensities?
A certain threshold has to be exceeded before a generator potential can be created in bipolar cells, which the rod cells are connected to. The number of rod cells connected to a single bipolar cell is great and this increases the chance that the threshold value will be exceeded to create a generator potential
What happens in rod cells to create a generator potential?
In order to create a generator potential, rhodopsin pigment in rod cells must be broken down. There is enough energy from low light intensity to cause breakdown
What are the limitations of many rod cells being linked to a single bipolar cell?
A limitation of many rod cells being linked to a single bipolar cell is the light received by these rod cells can only generate a single impulse to the brain, no matter the amount of neurones stimulated.
This means the brain is unable to distinguish between the separate sources of light that stimulated it and the two light sources that are close together cannot be resolved so rod cells have low visual acuity
How many types of cone cells are there and what does each cone cell respond to?
There are three types of cone cells, each responding to a different range of wavelengths of light
What pigment do all cone cells have? What are the three different colours of the iodopsin pigment? What do the three different colours absorb?
Cone cells all have the iodopsin pigment, but different colours of red, green and blue. The different colours all absorb different wavelengths of light
What is our perception of coloured images dependant on?
Depending on how big the proportions of each type of cone cell (red, green and blue) is stimulated, we perceive differently coloured images
Why do cone cells only respond to high light intensity?
Cone cells only respond to high light intensity and not to low light intensity, because iodopsin is only broken down if there is a high light intensity
Is each cone cell connected to a single or multiple bipolar cell? What does this connection to a single/multiple bipolar cell?
Each cone cell has its own connection to a single bipolar cell
What does this connection to a single/multiple bipolar cell cause the cone cells to have as a feature?
Cone cells have good visual acuity, as they are connected to a single bipolar cell, which means that if two adjacent cells are stimulated, the brain receives two separate impulses. This allows the brain to distinguish between the two light sources and gives the cone cells good visual acuity
Is the distribution of rod and cone cells even or uneven?
The distribution of rod and cone cells on the retina is uneven,
