09 | Sight Flashcards
how many ganglion cells do we have?
1.2 million
How many photoreceptors do we have?
130 million
5 cell types found in the retina
- photoreceptors
- horizontal cells
- bipolar cells
- amacrine cells
- ganglion cells
What are the only 2 retinal cells that can generate AP?
amacrine, ganglion
3 layers of the retina cells
- inner layer (photoreceptors)
- outer/middle layer (horizontal, bipolar, amacrine)
- ganglion layer
Fovea is densely packed with ___. No ___.
- cones
2. rods
fovea is a blind spot under…
dim light
function of fovea
fine discrimination
blind spot =
where optic nerve exits the eye (no rods or cones)
photopigment in rods
rhodopsin
photopigment in cones
pigment molecules
how much rhodopsin do we have?
10^8
what are more sensitive, rods or cones?
rods (can be activated by single photon)
What kind of special synapse does photoreceptors have?
ribbon
What is the special SNARE protein associated with ribbon synapses?
RIBEYE (makes up 2/3 of ribbon volume)
Which ion is responsible for the continuous depolarization in the dark?
Na
What is the Vm of photoreceptors?
-40 mV
What happens when light hits photoreceptors?
Close Na channels on outer segment -> hyperpolarization -> less NT release
Relationship between cGMP and channels on photoreceptors
- ↑ [cGMP] keeps Na channels open
* [cGMP] ∝ 1/intensity of light
Which NT is released by photoreceptors?
glutamate
Which NT is released by horizontal cells?
GABA
Which NT is released by bipolar cells?
glutamate
Which NT is released by amacrine cells?
DA or ACh
Which NT is released by ganglion cells?
glutamate (mostly)
Besides the typical NT, which other ones have been identified in the retina?
NO, BDNF
receptor fields help with…
fine discrimination/contrast
“on” ganglion cells =
center +, side -
“off” ganglion cells =
center -, side +
How many rods to 1 rod bipolar cell?
15-45
How many cones to 1 cone bipolar cell?
5-20
How many (cones or rods?) to 1 midget bipolar cell? What does it project to?
1 cone -> 1 midget bipolar cell -> specialized ganglion cell
What is the only area of the brain with inhibitory glu receptors? Which glu R is this?
bipolar cells (mGluR6)
What is it called when light hits the side of the center field?
annular illumination
are H bipolar cells on or off center?
off
Do H bipolar cells have excitatory or inhibitory mGluR?
excitatory
Which bipolar cell do rods project to?
D bipolar cells
How do rod bipolar cells typically interact with ganglion cells?
-> amacrine cells -> cone bipolar cells -> ganglion
Functions of horizontal cells
- regulate bipolar cell response to annular illumination
2. spatial resolution (contrast)
Horizontal cells are electrically coupled to ___ via ___
other horizontal cells via gap junctions
Effect of light on horizontal cells
- Light ⇒ photoreceptor hyperpolarize ⇒ horizontal cells hyperpolarize ⇒ ↓ GABA and NO release on surrounding photoreceptors ⇒ less inhibition ⇒ depolarization (small effect) (spread the response to light)
- The ↑ photoreceptor activity ⇒ ↑ NT ⇒ stimulate inhibitory mGluR6 ⇒ D bipolar cells hyperpolarize
What effect does NO secretion by horizontal cells have?
inhibit NT release from surrounding photoreceptors
Why does half of the ganglion cells hyperpolarize, and half depolarize in response to light?
Due to D and H bipolar cells (membrane potential of ganglion cell will change in the same direction as the bipolar cell it’s connected to)
Where does the connection go after ganglion cell?
-> lateral geniculate nucleus (LGN) cortex
What is contralateral innervation?
- Left visual field ⇒ right side of each retina ⇒ right LGN
* Right visual field ⇒ left side of each retina ⇒ left LGN
What is the disease where you lose 1/2 the visual field on the same side in both eyes?
homonymous hemiopsia
Damage to right cortex will cause blindness in ___ visual field
left
Where is LGN located?
thalamus
