Studied by 1 person
What are the two types of receptors in the eye?
Photosensitive cells: rods and cones. They are found over most of the retina under layers of muscle/nerve fibre.
How is the fovea different to other areas of the retina?
The fovea is a small depression in the retina containing only cone cells.
How is the blind spot different to other areas of the retina?
The blind spot has no photosensitive receptors.
What is the function of the optic nerve?
To carry action potentials to the brain.
What are rod cells and how many types are there?
Rod-shaped photoreceptors in the eye. There is one type.
How many rod cells are there in one eye and where are they found?
125 million rod cells per eye. They are found over the whole retina except for the fovea and blind spot. There are more rods on the periphery/edges of the retina.
Describe the visual acuity of rod cells and their sensitivity to light.
Rods have a low visual acuity. They are the most sensitive to low light intensity (more sensitive than cones).
Describe the pigment and colour vision of rod cells.
They contain a pigment called rhodopsin which can change shape into opsin/retinal in light. The pigment that was bleached in the light can turn back to rhodopsin in the dark. They produce black and white vision.
What are cone cells and how many types are there?
Cone-shaped photoreceptors in the eye. There are three types:
red-sensitive
blue-sensitive
green-sensitive
How many cone cells are there in the eye, and where are they located?
They are found in the fovea, and there are 7 million per eye.
Describe the visual acuity and light sensitivity of cone cells.
Cones have a high visual acuity. They are sensitive to high light intensity (less sensitive than rod cells).
Describe the pigment in cone cells and their colour vision.
Cones contain a pigment called lodopsin which breaks down in very high light levels to create a generator potential. They produce colour vision.
How are cone cells connected to bipolar neurones in the retina?
One cone cell connects synapses with one bipolar neurone.
How are rod cells connected to bipolar neurones?
Several rod cells connect synapses with one bipolar neurone.
What are bipolar neurones?
Bipolar neurones connect to ganglion cells which lead to the optic nerve (which connects the eye to the brain).
What is visual acuity?
how far apart two spots of light must be to be seen separately
higher visual acuity means the image is seen in a higher resolution
How is visual acuity in rod cells linked to their connection with the bipolar neurone?
only a single impulse is generated as many rod cells connect to one bipolar neurone
this means that they cannot interpret which rod cell was stimulated and two dots of light close together will appear as a single blob
Why are many rods connected to a single ganglion cell?
A single rod cell is unlikely to generate a large enough general potential to conduct a nerve impulse. When a group of rod cells is stimulated by dim light, the combined generator potential is large enough to meet the threshold of the ganglion cell --> SUMMATION.
How is visual acuity in cone cells linked to their connection with the bipolar neurone?
as cone cells are connected to bipolar neurones individually, the brain receives separate impulses from each cell
this means that they have a high visual acuity as for each cone stimulated the brain sees a dot of light
How does colour-blindness work?
Person is missing a certain type of cone cell.
