lecture 15- visual system sensory III

Question 1

Optic disk (blind spot)

Answer 1

area where optic nerve and blood vessels leave the eye

Question 2

lens

Answer 2

bends light to focus it on the retina

Question 3

Zonules

Answer 3

attach lens to ciliary muscle

Question 4

pupil

Answer 4

changes amount of light entering the eye

Question 5

retina

Answer 5

layer that contains photoreceptors

Question 6

sclera

Answer 6

is connective tissue

Question 7

how does light enter the eye

Answer 7

the cornea and lens focus light rays onto the retina

specialized cells in the retina (photoreceptors) transduce light energy into an electrical signal

a network of neurons collect electrical signals to be transmitted along the optic nerve to the brain

Question 8

how is light refracted when it enters the eye?

Answer 8

refracted twice
2/3 cornea (large difference in refractive index)
1/3 by lens (large curvature)

Question 9

accomodation

Answer 9

the lens can change its shape to focus onto the retina
(due to contraction and relaxation of the ciliary muscle

Question 10

ciliary muscle

Answer 10

a right of smooth muscle surrounding the lens

Question 11

presbyopia

Answer 11

loss of accommodation due to loss of elasticity

Question 12

what happens when ciliary muscle is relaxed

Answer 12

the lens is flattened
–> more distant objects are focused on the retina

Question 13

when ciliary muscle contracts

Answer 13

the lens is rounded
–> closer objects are focused on the retina

Question 14

concave lens

Answer 14

scatters light rays (diverges)

Question 15

convex lens

Answer 15

light rays diverge

Question 16

Light from center of field of view is focused on the

Answer 16

fovea

Question 17

area of most acute vision and center of visual field

Answer 17

fovea and macula

Question 18

does the fovea have neurons or blood vessels?

Answer 18

no

Question 19

Rods and cones

Answer 19

sensory cells (photoreceptors)
- transduce light energy into electrical signal
- only produce graded potentials

Question 20

Bipolar cells, amacrine cells, horizontal cells

Answer 20

• connect sensory cells to transmitting cells, process and integrate information, converge signals from several photoreceptors

Question 21

Ganglion cells

Answer 21

transmitting cells (output to CNS)
- carry information via the optic nerve to the brain
- produce action potentials

Question 22

info from —- rods and cones converges on —– ganglion cells

Answer 22

100 million rods and cones
1 million ganglion cells

Question 23

the size of the receptive field depends on…

Answer 23

the location on the retina

Question 24

compare ganglion cell receptive fields in the periphery vs in the fovea

Answer 24

ganglion cells in the periphery have large receptive fields

ganglion cells in the fovea have very small receptive fields

Question 25

Rods are responsible for

Answer 25

low light/night vision

Question 26

rhodopsin

Answer 26

is a photopigment that is the signal transducer

Question 27

Cones are responsible for

Answer 27

sharp vision and colour vision

Question 28

3 types of cones

Answer 28

each has a different photopigment (related to rhodopsin) and responds to specific colour (red, blue, green)

Question 29

what does light do to rod and cone cells?

Answer 29

it hyperpolarizes them

Question 30

What is rhodopsin? 2 components

Answer 30

opsin + retinal

opsin is the GPCR
retinal is the visual pigment

Question 31

when opsin and retinal are tightly bound, rhodopsin is

Answer 31

inactive

Question 32

disks are the location of —- in rods

Answer 32

signal transduction

Question 33

rods and cones transduce

Answer 33

light photons into electrical currents

Question 34

rods and cones project to

Answer 34

bipolar cells

Question 35

bipolar cells synapse with

Answer 35

ganglion cells

Question 36

ganglion cell axons from the

Answer 36

optic nerve and project to the CNS

Question 37

Phototransduction in rods
(in darkness)
7 steps

Answer 37

1. retinal and opsin are bound
   - rhodopsin is inactive
2. cGMP levels inside the cell are high
3. CNG channels are open
4. rod cell is depolarized (-40mV)
5. V-gated Ca2+ channels are open
6. Ca2+ goes into the cell
7. NT (glutamate) is released

Question 38

phototransduction in rods
(in the presence of light)
9 steps

Answer 38

-retinal phtotoisomerizes (11-cis –> trans) causes a conformation change in the intracellular C-terminus of rhodopsin

1. rhosopsin is activated (retinal is released)
2. activates associated G protein: transducin
3. transducin activates phosphodiesterase
4. phosphodiesterase breaks down cGMP
5. decreased [cGMP] –> CNG channels close
6. cell hyperpolarizes
7. voltage gated Ca2+ channels close
   (less Ca2+ into cell)
8. Decreased NT (glutamate release)
9. adjacent bipolar cell and ganglion cell are excited