Vision Flashcards
What can we see?
Contrast
What is the pathway of light to the brain?
Light -> Photoreceptor -> Bipolar cell -> Ganglion cell
What are the two types of lateral connections found in the visual system?
Horizontal cells
Amacrine cells
Where are horizontal cells found?
Link 2 photoreceptors or bipolar cells
Where are amacrine cells found?
Link 2 bipolar, ganglion cells or amacrine cells
How do AP and NT release relate to light levels?
Dark = more current therefore more AP therefore more NT
Light- turns off Na channels therefore less current therefore less AP and NT
What two types of photoreceptor do we have?
Rods and cones
When are rods used?
Dim light
When are cones used?
Day light
Does one ganglion receive input from one photoreceptor?
No
How many cones go to one ganglion?
Few. Therefore high acuity
How many rods go to one ganglion?
Many. Therefore low acuity but high sensitivity
How do we detect different colours?
DIfferent opsins that respond differently to different wavelengths
What five things can summarise cones?
Chromatic Central retina Low convergence Low light sensitivity High visual acuity
What five things can summarise rods?
Achromatic Peripheral retina High convergence High light sensitivity Low visual acuity
What two pathways are present in the visual pathway?
Off pathway
On pathway
Describe off pathway
Dark: More glutamate from photoR -> IonotropicR on bipolar cells depol them -> Depol ganglion cells
Light decrease signal
Describe on pathway
Dark: More glutamate from photoR -> MetabotropicR on bipolar cells hyperpol them -> hyperpol ganglion cells.
Light increase signal
Why is lateral inhibition important?
To decrease noise
Describe lateral inhibition
Strong stimuli in the middle increases inhibition of neighbouring cells while less stimuli on neighbouring cells inhibit central less
What do horizontal cells do and release?
Inhibitory interneurons
GABA
What NT do photoreceptors release?
Glutamate
Explain center surround organisation
Light inhibits glutamate release in the centre therefore activates ‘On’ bipolar cells. Neighbouring photoreceptors don’t receive light therefore release glutamate onto horizontal cells which release GABA to central PR thus decreasing glutamate even more.
