L4 - Vision Flashcards
What receptor do ON bipolar cells have and what does this do?
mGluR6 which converts the hyper-polarisation to a depolarisation.
What receptor do off bipolar cells have and what does this do?
mGlu R1 and R2 which conserve the hyperpolarization
What are the cells in the eye which generate APs?
Amacrine cells and retinal ganglion cells
How do ribbon synapses adapt to light?
They destabilise releasing synaptic spheres thus shortening the synapse.
What is the function of the centre surround receptive field?
Emphasize edges
What is APB and what did it show?
APB is. Glutamate analogue which specifically blocks mGluR6 on bipolar neurons. It was used to determine the function of on and off bipolar cells. When used it was found that an increased light response was dramatically reduced where as a decreased light response was unaffected. This disproved the separate channel model and instead suggested that horizontal cells are responsible for on/off centre receptive fields
What’s the role of glia in the eye?
Provide a soft substance for neurites to grow
K homeostasis thus Elevating the signal to noise ratio
Retinal volume homeostasis
Take up glutamate
Outline one of the responses that Müller cells have to Ca
Glial calcium release is triggered by light. This may lead to the release of gliotransmitters such as: glutamate, atp/Adp/adenosine, d-serine. This may lead to neuronal adaptation to elevated light levels.
Describe midget cells
Account for 80% of retinal ganglion cells
Go from the ganglion cell layer of the retina to the parvocellular layers of the LGN.
Slow conduction velocity
Respond to changes in colour
Respond weakly to changes in contrast
Small dendritic trees
Describe parasol cells
10% of retinal ganglion cells Ganglion cell layer of the retina to the magnocellular layers of the LGN Fast conduction velocity Motion detection Major inout for the MT cortex
How do photoreceptors respond to a light stimulus?
They hyperpolarise with a graded potential
What is the midget:parasol ratio at the fovea?
8:1
What is the midget to parasol ratio at the periphery?
1:1
What do ribbon synapses enable?
Analogue signal transfer at photoreceptors
Where is the visual cortex located?
In the occipital lobe at the back of the skull
Outline Hubel and Wiesel’s experiment
The demonstrated the orientation selectiveness of V1 cortical neurons using a cat and a beam of light. The beam of kig ht moved across the visual field. They found thay the neurons only fired when the line was in particular place on the retina, the activity of the neurons changed depending on the orientation of the line and sometimes the neurons only fired when the line was travelling in a certain direction.
What are the transforms in V1?
Orientation, direction, spatial frequency, binocularity, on/off convergence and midget/parasol convergence.
Outline the three models for the structure of the V1 cortex
The ice cube model suggests that the ocular dominance columns are arranged in a rigid cube like structure
The swirl model suggests a model similar to the ice cube however not as rigid, more bent.
The radial model
Describe the features of v4
Large receptive fields
Task and intent modulated
Response can be modulated by eye movements
Not exclusively a colour area
What is the function of the MT/V5 cotrex?
Integration of direction selective input - flicker, motion and depth
What are the basic visual capacities?
Colour Brightness Hue Pattern Motion Depth
What are the intermediate visual capacities?
Consistance Selection Recognition Transposition Comparison Location
What are the 3 qualities of colour?
Hue
Brightness
Saturation
Why are there no blie cones in the central macula?
Blue light input is less accurate
