KD - Vision II Flashcards
Rods (2) vs Cones (5)
Rods:
- low spatial resolution
- High sensitivity (1 photon)
Cones:
- High spatial resolution
- Low sensitivity (>100 photons)
- Less saturation
- Rapid recovery
- Colour vision
What is the range of light intensities that human vision can perceive?
Human vision can perceive over a range of approximately 12 logs of intensities
What visual impairment is associated with the loss of rod and cone function?
Loss of rod function = night blindness
Loss of cone function = legally blind
What are features of cones and what types are there?
Each cone is monochromatic (detects one colour)
3 cones: (Trichromatic)
- Short wavelength (blue)
- Medium wavelength (green)
- Long wavelength (red)
Where are Medium and Long wavelength cones located?
On the X-chromosome
Is photoreceptor density constant across the retina?
No
Concentration of cones is higher at the fovea
- As you move away the concentration decreases
However the concentration of rods at the fovea is low
- As you move away it increases
What type of information is primarily encoded by retinal circuits?
Retinal circuits primarily encode light-dark information rather than color
What is composed in the simplest retinal circuit? (3)
Photoreceptor to bipolar cell to retinal ganglion cell
What do ganglion cells in the retina detect?
Changes in luminance
What is a receptive field?
Region in which a stimulus elicits an AP
How do on-center and off-center ganglion cells respond to light stimuli?
1) On-center Ganglion Cell
- If the centre is brighter than the surround, then an AP is elicited
(shuts down when centre is darker)
2) Off-center Ganglion Cell
- If the centre is darker than the surround, then an AP is elicited
(shuts down when centre is brighter)
What causes the adverse affects in on-centre and off-centre ganglion cells? (2)
- On/ off-center bipolar cells
- Different glutamate receptors
What occurs in the On-centre pathway and the Off-centre pathway?
On-center: sign-inverting
- mGluR6 receptor inhibited (-)
- On-centre bipolar cell depolarised
- On-center ganglion cell stimulated (+)
Off-center: sign-conserving
- AMPA kainate receptor-stimulated (+)
- Off-centre bipolar cell hyperpolarised
- Off-centre ganglion cell stimulated (+)
What cells are responsible for light adaptation?
Horizontal cells
What are 3 features of horizontal cells?
- Connected via gap junctions
- Network over large area of retina
- Allows detection of background illumination
