09 | Sight

Question 1

how many ganglion cells do we have?

Answer 1

1.2 million

Question 2

How many photoreceptors do we have?

Answer 2

130 million

Question 3

5 cell types found in the retina

Answer 3

1. photoreceptors
2. horizontal cells
3. bipolar cells
4. amacrine cells
5. ganglion cells

Question 4

What are the only 2 retinal cells that can generate AP?

Answer 4

amacrine, ganglion

Question 5

3 layers of the retina cells

Answer 5

1. inner layer (photoreceptors)
2. outer/middle layer (horizontal, bipolar, amacrine)
3. ganglion layer

Question 6

Fovea is densely packed with ___. No ___.

Answer 6

1. cones

2. rods

Question 7

fovea is a blind spot under…

Answer 7

dim light

Question 8

function of fovea

Answer 8

fine discrimination

Question 9

blind spot =

Answer 9

where optic nerve exits the eye (no rods or cones)

Question 10

photopigment in rods

Answer 10

rhodopsin

Question 11

photopigment in cones

Answer 11

pigment molecules

Question 12

how much rhodopsin do we have?

Answer 12

10^8

Question 13

what are more sensitive, rods or cones?

Answer 13

rods (can be activated by single photon)

Question 14

What kind of special synapse does photoreceptors have?

Answer 14

ribbon

Question 15

What is the special SNARE protein associated with ribbon synapses?

Answer 15

RIBEYE (makes up 2/3 of ribbon volume)

Question 16

Which ion is responsible for the continuous depolarization in the dark?

Answer 16

Na

Question 17

What is the Vm of photoreceptors?

Answer 17

-40 mV

Question 18

What happens when light hits photoreceptors?

Answer 18

Close Na channels on outer segment -> hyperpolarization -> less NT release

Question 19

Relationship between cGMP and channels on photoreceptors

Answer 19

• ↑ [cGMP] keeps Na channels open

* [cGMP] ∝ 1/intensity of light

Question 20

Which NT is released by photoreceptors?

Answer 20

glutamate

Question 21

Which NT is released by horizontal cells?

Answer 21

GABA

Question 22

Which NT is released by bipolar cells?

Answer 22

glutamate

Question 23

Which NT is released by amacrine cells?

Answer 23

DA or ACh

Question 24

Which NT is released by ganglion cells?

Answer 24

glutamate (mostly)

Question 25

Besides the typical NT, which other ones have been identified in the retina?

Answer 25

NO, BDNF

Question 26

receptor fields help with...

Answer 26

fine discrimination/contrast

Question 27

"on" ganglion cells =

Answer 27

center +, side -

Question 28

"off" ganglion cells =

Answer 28

center -, side +

Question 29

How many rods to 1 rod bipolar cell?

Answer 29

15-45

Question 30

How many cones to 1 cone bipolar cell?

Answer 30

5-20

Question 31

How many (cones or rods?) to 1 midget bipolar cell? What does it project to?

Answer 31

1 cone -> 1 midget bipolar cell -> specialized ganglion cell

Question 32

What is the only area of the brain with inhibitory glu receptors? Which glu R is this?

Answer 32

bipolar cells (mGluR6)

Question 33

What is it called when light hits the side of the center field?

Answer 33

annular illumination

Question 34

are H bipolar cells on or off center?

Answer 34

off

Question 35

Do H bipolar cells have excitatory or inhibitory mGluR?

Answer 35

excitatory

Question 36

Which bipolar cell do rods project to?

Answer 36

D bipolar cells

Question 37

How do rod bipolar cells typically interact with ganglion cells?

Answer 37

-> amacrine cells -> cone bipolar cells -> ganglion

Question 38

Functions of horizontal cells

Answer 38

1. regulate bipolar cell response to annular illumination | 2. spatial resolution (contrast)

Question 39

Horizontal cells are electrically coupled to ___ via ___

Answer 39

other horizontal cells via gap junctions

Question 40

Effect of light on horizontal cells

Answer 40

* 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

Question 41

What effect does NO secretion by horizontal cells have?

Answer 41

inhibit NT release from surrounding photoreceptors

Question 42

Why does half of the ganglion cells hyperpolarize, and half depolarize in response to light?

Answer 42

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)

Question 43

Where does the connection go after ganglion cell?

Answer 43

-> lateral geniculate nucleus (LGN) cortex

Question 44

What is contralateral innervation?

Answer 44

* Left visual field ⇒ right side of each retina ⇒ right LGN | * Right visual field ⇒ left side of each retina ⇒ left LGN

Question 45

What is the disease where you lose 1/2 the visual field on the same side in both eyes?

Answer 45

homonymous hemiopsia

Question 46

Damage to right cortex will cause blindness in ___ visual field

Answer 46

left

Question 47

Where is LGN located?

Answer 47

thalamus