Lecture 8 - Retina And Vision Flashcards
What do retina Contain?
Light sensitive cells
Photoreceptors, blue light sensitive RGCs
What else do retina Contain?
Neural network
Including bipolar, amacrine, horizontal cells
Output cells (retinal ganglion neurons) rhode axons form the optic nerve
How many major classes of neuron in the retina?
5
What does photoreceptors transduce?
Light
What makes synaptic connection onto a bipolar cells?
Cones
What are bipolar cells?
Special neuron in the retina
What connects from the photoreceptors to the retinal ganglion cells?
Bipolar cells
What is the vertical pathway?
Information flow through the retina
What layers are present on top of the retina where light strikes first?
Nerve fibre layer
Retinal ganglion cells
What must light go through to get to the light receptor cells?
All the neurophil
Where do you find almost 100% myelination?
Optic nerve
Where do nerve fibre become myelinated as they pass through the retina?
laminar cribosa
Why is axon with no myelin bad?
There is continuous conduction occurring in the axon
Obscures codon
What kind of axon are present in the visual system?
Myelinated and unmyelinated
What are horizontal cells?
Laterally interconnecting neurons
Cell bodies present in the inner nuclear layer of retina
What does horizontal cells help integrate and regulate?
Input from multiple photoreceptors cells
What does horizontal cells allow?
Eyes to adjust to see well under both bright and dim light conditions
What does horizontal cells provide?
Inhibitory feedback to rod and cone photoreceptor
What is photo pigment made from?
protein opsin
Derivative of vitamin A
What is protein opsin?
Encoded in our DNA
Protein that bind to light-reactive chemical to underlie vision
Derivative of vitamin A
Retinal
Exist in 2 isomers (cis/trans)
Several different … encoded by different genes
Opsins
Why is isomerization crucial?
When the retinal is in the cis form
It absorbs photons and changes into trans form
The whole complex transduces the photons that has been absorbed
In our light receptors called cones, how many different types of opsins present?
3
What are the 3 receptors in the retina that are responsible for the perception of colour?
One receptor is sensitive to colour green
Another blue
Another red
What is the most common form of colour blindness?
The loss of ability to see green
What is trichromatic vision?
Sensitive to three of the colours
Have perception of three primary colours
Normal human vision
What happens when L is missing?
Unable to distinguish red from green
What is Rhodoxin sensitive to?
Low levels of light
What is Ishihara plate?
A classic device for testing colour blindness
What is a photomultiplier tube?
A photo emissive device in which the absorption of a photon results in the emission of an electron
Sensitive to the arrival of photons
As are retinal photoreceptors
What does photoreception allow?
Large amplification
What do we see in the output of retina?
Eigengrau ‘intrinsic light’
See a foggy grey
What is the retina sensitive to?
Both light and dark
Which one has more activity in the retina?
Dark
What is a good stimuli for activating the human visual system?
Checker boards
What makes the 3 light sensitive system?
Rods
Cones
RGC blue light sensitive neurons
What is cones?
Evolutionarily older photoreceptors
What can Rods not able to respond to?
Light intensity fluctuations of 12Hz
What is present across the surface of retina?
Blood vessels
What does the neuron network and the photoreceptors require?
Oxygen
What is the optic cup?
White
Cup-like area in the centre of the optic disc
What is the optic disc?
The point in the eye where the optic nerve leaves the retina
What is the Fovea?
Located in the macula of the retina that provides the clearest vision of all
Highest number of photoreceptors
High density of cones
High acuity and colour vision
What does retinal plan and light intensity fluctuation processing show?
basic vertical transfer of the information flow in the retina
What is light intensity fluctuation broken down into?
Separate frequency channels by the membrane properties of bipolar cells
What is band-pass filtering?
All information passes to RGCs via the bipolar cells
What can RGCs do?
Keep fluctuation frequency information separate and parallel
Or recombine before sending to brain
What are vertebrate retinas dominated by?
rods
How many types of cones does FISH have?
4
What did primates re-evolve?
Trichromatic vision
What are cones
Not wavelength selective
Selective to white light over whole of visual spectrum
What are retinal ganglion cells?
- On-centre, off-surround
2. Off-centre, on-surround
What does retinal ganglion cells require?
Inhibitory horizontal and amacrine neurons
What does lateral inhibition highlight?
Intensity boundaries
What does Mach bands do?
Optical illusion
Exaggerates the contrast between edges of the slightly differing shades of grey
Triggers the edge-detection in the human visual system
Illusion brought about by lateral inhibition
What did Herring postulate?
There was a light system and dark system
The balance between these antagonistic system gives us perceived light intensity
What is on-centre?
RGC responds to light
What is off-centre?
RGC responds when the light is switched off
What does retina have several types of?
RGC in an array covering entire field
What does the idea of antagonistic system impact?
Colour vision
Sensitivity to motion
What is how colours perceived based on?
Opponent colour theory
When does retinal ganglion cell give an output?
When you have a blue light shining on the centre of the surrounding inhibitory field
What is the blue cone doing?
Exciting the RGCs
What is the red and green cone doing?
Inhibiting
What may retinal ganglion cell sensitive to?
Yellow light
Receiving information from blue photoreceptor which is inhibitory
Retinal ganglion cells (yellow)
received information from red and green cones which are excitatory
What does the opponent colour theory suggest?
Colour perception is controlled by the activity of 2 opponent system:
Blue-yellow mechanism
Red-green mechanism
Surround inhibition
The network predicts what will be found in the centre of the field, and only when the illumination at the centre differs from what is predicted is a signal generated
What is reducing redundancy?
Sending only interesting or important information to the brain
What is the first relay point for visual information heading towards the cortex?
Retina
LGN nucleus
Where is the information passed to next?
Brodmann area 17 Striate Cortex (V1)
What does V1 have?
Neurons that are tuned to bars and edges moving or orientated in the correct way
Where does information from those cells (V1) go to?
Area 18 and 19 (V2 and V3)
What did Hubel and Wiesel (1962) study?
The effects of edges in the visual world and how edges were processed
What is orientation tubing a measure of?
How a cell is firing rate depends on the orientation of a stimulus
Why does amacrine cells have very long axons?
Bring information from a distant site on retina to our retinal ganglion cells where comparisons can be made
It compares what is going on in the centre of vision with what is going on in the background
What is motion blindness?
Medical condition where a person cannot see objects that are moving even though they can see the objects that do not move
Related to nerves
What is Melanopsin?
Retinal ganglion cells which are sensitive to blue light
Connect to SCN neuron
What 2 neurotransmitters do Melanopsin use?
Glutamate
Pituitary adenylate cyclase activating peptide (PACAP)
What does neurotransmitters affect?
The firing behaviour of SCN neuron
What happens when SCN neuron is excited by RGC?
An increase in calcium inside the SCN neuron
Kinase activation
CREB phosphorylation
What is CREB?
A protein that is activated by phosphorylation
Activates protein expression (gene expression)
What is E-box?
A region of DNA that is controlling whether this gene is going to be expressed
What is CRE?
Camp response element
What is PER expression?
Controls the expression of other proteins including that of C-B
SCN neuronal activity changes
Electrically silent at night
Firing during the day
Achieved through rhythmic changes in ion channel expression and phosphorylation
