The Eye Flashcards
What are the light receptors in the eye
Rods and cones
Why are the rides and cones also transducers
They convert light energy into the electrical energy of a nerve impulse
What are light sensitive pigments
They breakdown when exposed to certain intensities or wavelengths of light
Where do pigments breakdown
Photoreceptors
What does the breakdown of pigment in the photoreceptors trigger
Generator potential in bipolar neurones they synapse with
What do bipolar neurones synapse with
Sensory neurones in the optic nerve which directly connect with the brain
What photosensitive pigment do rod cells contain
Rhodopsin
What does rhodopsin detect and in what light intensity
Detect light at very low light intensity
How do rod cells cross the threshold value to reduce a generator potential
- low light intensity has enough energy to breakdown rhodopsin
- retinal convergence occurs
What is retinal convergence
A number of rods are connected to 1 bipolar neurone which gives a greater chance of crossing the threshold in the bipolar neurone and creating a generator potential
Why must a the threshold value be crossed
To make sure generator potential occurs leading to a action potential being transmitted to bipolar neurone and impulse goes to the brain
Explain why rod cells don’t see colour
Cannot distinguish differences between wavelengths of light therefore images appear in back and white
What type of intensity to cone cells respond to
High light intensity
What photosensitive pigment do cone cells contain
Iodopsin
Why do cone cells only respond to high light institute
Iodopsin in cone clls is only broken down at high light intensity
They are each connected to a single bipolar neurone so stimulation of a number of cone cells can’t be combined to exceed the threshold value = low retinal convegance
How do cone cells allows us to see colour
- 3 different type of cone each witch different type of Iodopsin
- each type of Iodopsin is sensitive to a specific range of wave lengths
- depending on proportion of each type of stimulation we see imagines in full images
What is trichromatic theory
- depends on colour mixing of the primary colour green red and blue
- Proposes there are 3 types of of cone sensitive to three wavelengths, if one of these types is stimulated on its own we will see that colour
What is colour seen also determined by
Excitation of the 3 receptors
Red
Cone sensitive to red
Green
Cone sensitive to green
Blue
Cone sensitive to blue
Yellow
Cone sensitive to red and green
Cyan
Cone sensitive to green and blue light
Magenta/purple
Cone sensitive to blue and red light
White
Cone sensitive to red blue and green light
What is visual acuity
The ability for the eye to resolve 2 or more stimuli separated spatially
Are cones or rods responsible for visual acuity
Cones
Why do rod cells give low visual acuity
- objects cannot be distinguished as separate due to low visual acuity
- connected to same bipolar neurone = high density
- light received fro rod cells sharing same cell only generate a singe impulse regardless of number of rods that are stimulated
High visual acuity
- Objects can be distinguished as separate due to high visual acuity
Connected to separate bipolar neurones - low sensitivity
What part of retina are cones situated
The fovea
Rod connection
- high retinal conveyance
- greater chance threshold value is reached at low light intensity = high sensitivity
- low visual acuity
Cone connection
- low retinal convergence
- Smaller chance of threshold value will be reached at low light intensity = low sensitivity
- high visual acuity
Importance of fovea
Enables accurate vision in bight light and colour vision
What allows us to detect objects in ver low light
Retinal convergnace - many rods synapse to a single neurone
What allows us to distinguish between points very close together
Visual acuity - one cone synapses to a singe neurone
