L4 - Vision overview Flashcards
What are the 3 types of stimuli recognised by the visual system? (3)
-Food
-Predator
-Mate
What is the processing level organisation in the visual system?
-Positive feedforward
-Negative feedback
-Negative feedforward
What part of the visual system sends information to the brain?
Optic nerve
What is the main function of the retina
Image acquisition
What part of the brain preprocesses visual information
Lateral geniculate nucleus (LGN)
Where does main processing of visual information happen in the brain?
Visual cortex
What part of the brain does the right hemifield activate?
Left brain (and vice versa)
What are the two main visual pathways in the cortex? (2)
and what do they do? (2)
and where are they found (2)
Ventral - “what” (V1,V2 and V4) - Inferior temporal
Dorsal - “where” - Posterior parietal
What dos the pupil do?
Pupil regulate the amount of light that falls on the retina
What does the lens do?
Lens focuses image on the fovea
What does the Fovea do?
Fovea is a part of the retina with highest visual acuity
What part of eye does light travel through?
Which cells does light go through?
-The retina
-Light can’t travel through most of retina only Muller cells
What do the 5 layers of the retina consist of?
3 layers of neutrons
2 layers of synapses
What cells are ‘feedforward neurones’? (3)
-Photoreceptors
-Bipolar cells
-Ganglion cells
(Photoreceptors signal with bipolar cells which signal with ganglion cells)
(Glutamate expressed in the bipolar cells activate the ganglion cells)
What cells are ‘feedback neurones’? (2)
Horizontal cells
Amacrine cells
What are the two layers of synapses known as? (2)
What are they made up of? (2)
Inner and Outer plexiform layers
Outer plexiform layer consist of synapses between photoreceptors, bipolar cells and horizontal cells
Inner plexiform layer contains synapses between bipolar cells, amacrine cells and ganglion cells
What do Amacrine cells express? and do? (2)
-Amacrine cells express GABA
-They send information back and forward and directly inhibit the ganglion cells
Where do bipolar and horizontal cells receive input from?
Where do ganglion and marine cells receive input from?
Bipolar and horizontal cells receive input from photoreceptors in the outer plexiform layer (OPL)
Ganglion cells and amacrine cells receive input from bipolar cells (and ganglion cells from amacrine cells) in the inner plexiform layer (IPL)
What are the two types of photoreceptor in the retina? (2)
When are they active? (2)
-Rod and cone cells
-Rods are active at dim light and cones are active at bright
Where does phototransduction happen in rod and cone cells?
How does this work?
-The outer segment
-cGMP activates specific ion channel to cause hyperporlarisation/depolarisation
What is the phototransduction mechanism?
-ON bipolar cells depolarise when light goes on and OFF bipolar cells hyper-polarise
-Photoreceptor hyper-polarise in response to light
-Less glutamate the less its active
-Some cells have different response and their membrane potential increases
What is the phototransduction mechanism? (2)
-ON bipolar cells depolarise when light goes on and OFF bipolar cells hyper-polarise
-Photoreceptor hyper-polarise in response to light
Less glutamate the less its active
Some cells have different response and their membrane potential increases
What is released by rod and cone cells in the dark?
Constant release of glutamate in darkness
(less released during activation by light)
How does the mechanism of On cell activation differ from photoreceptors? (3)
-ON cells express mGluR instead of AMPAR to signal a cascade, using a G protein cascade
-G-protein (Go), not the same as in photoreceptor cascade
-Removal of cGMP is not required for ion channel closure
Various candidates:
TRPM1: expressed in ON but not OFF cells
Nyctalopin, proteoglycan required for light and glutamate responses in ON cells
What gene is required in response for ON channels?
TMPR1
What is the mechanism of ON cell activation? (4)
-Flashes of light leads to activation of bipolar cells
-Axons of ON bipolar cells and dendrites of ON ganglion and amacrine cells are located in the same sub-laminae in the inner plexiform layer
-ON and OFF cells project into different parts of the plexiform layer
-There are different types of ganglion dendrites
Where are the axons of ON bipolar cells and dendrites of ON ganglion and amacrine cells located?
In the same sublaminae in the IPL (inner plexiform layer)
When will retinal ganglion cells fire APs?
When specific areas of the retina are illuminated
(centre surround receptive field) - centre normally cell body
What do different parts of the receptive field do when stimulated? (2)
Bipolar and ganglion cells have centre surrounded organisation
Spot (centre) - depolarisation
Annulus (surrounding ) - hyperopolarisation
