Systems Lecture 4

Question 1

how many photoreceptors in retina

Answer 1

100 million

Question 2

how many photoreceptors in afferent axons

Answer 2

1 million - convergence from retina to axon

Question 3

binocular vision is what

Answer 3

two images- allows us to have depth perception

Question 4

general flow of visual information

exceptions?

Answer 4

retina –> lateral geniculate nucleus –> area 17/ V1/ striate cortex –> 2 dozen other cortical areas

although some connections bypass thalamus (LGN) - although these ones do not help us see things

Question 5

how light info goes through cell types in retina

Answer 5

photoreceptors (outside of retina; closest to brain) –(horizontal cells) –> bipolar – (amacrine) –> ganglion

Question 6

photoreceptors to bipolar cells is what type of communication

Answer 6

chemical

Question 7

ganglion cells communicate how

Answer 7

electrically - action potentials

Question 8

cell type to cell type; antagonistic vs same activation

Answer 8

photoreceptor –> bipolar (antagnositic)

bipolar –> ganglion (same)

Question 9

what is the purpose of lateral cell communication - horizontal cell and amacrine cells

Answer 9

they are “gate keepers” cam influence the degree of inhibitory or excitatory synapses by modulating release of neurotransmitters in the synaptic cleft

Question 10

source of output from retina?

other communication in eye?

Answer 10

ganglion cells only - electrical communication through action potentials
- others hyperpolarize of depolarize depending on light - chemical communication - neurotransmitter release proportional to hyperpolarization and depolarization

Question 11

lining in back of eye ____ is important for what

Answer 11

melanin - deflecting light - limits light scattering in back of retina

Question 12

rods:

Answer 12

more sensitive for light - responsible for night vision (scoptic vision) - no colour - short- more rods than cones - lots of convergence in order to detect any light

Question 13

cones:

Answer 13

longer than rods; less of them than rods; 3 photopigments (short, medium long responsive to different wavelengths); daytime vision (photopic vision)
- high acuity in central field bc there are many cones

Question 14

fovea:

Answer 14

best acuity if light hits here; full of cones; no rods; pit in fovea to help reduce light defraction to photoreceptors/ cones and/or to minimize interference of light passing through other cells

Question 15

mesopic
scoptic
photic
light conditions and corresponding photoreceptors

Answer 15

mesopic- both rods and cones; low lght

scoptic - night vision - rods

photic - light conditions- cones

Question 16

high level of rods where on retina

Answer 16

periphery - why in dark you see more in your peripheral vision

Question 17

spot with no photoreceptors in eye

Answer 17

blind spot- where optic nerve exits eye

Question 18

rods or cones more convergence

Answer 18

rods - need to be very light sensitive - only need small amount of light to activate ganglionic cells

Question 19

ON center bipolar cell receptor? how does this respond to the presence of light

Answer 19

metabotropic -
light–> cone, hyperpolarizes, no glutamate - they are no open and are excited
- called ON center because light turns them on - rapid firing

Question 20

OFF center bipolar cell receptor? response to light?

Answer 20

ionotropic glutamate receptors (glutamate gated)- light –> photoreceptors –> hyperpolarize –> no glutamate–> cant open receptor –> inhibited
OFF bc light turns them off - reduced firing

Question 21

in response to light, photoreceptors

Answer 21

light- hyperpolarize - no glutamate released

dark - depolarize - glutamate released

Question 22

why is the receptive field surround antagonistic to receptive field center?

Answer 22

surround - bilateral connection by horizontal cells to bipolar cells - photoreceptor –> horizontal (same activation) horizontal –> bipolar (same activation)

Question 23

inhibition of bipolar cell activation reduces firing, no firing only occurs…

Answer 23

in response to cancellation from surround when center is on - has to be equally covered

Question 24

when dark completely coves the receptive field - surround and center - is the response cancelled?

Answer 24

no bc surround has more real-estate

Question 25

P type ganglionic cells

Answer 25

smaller than M type
have a more prolonged response to light - sustained action potential firing as long as stimulus is present
90% prevalent; slower I optic nerve than M type

Question 26

M type ganglioniccells

Answer 26

larger than P type cells 5% prevalent

fast transient response to light - sensitive to low light; faster in optic nerve than P type

Question 27

where are M and P cells locate in visual system

function?

Answer 27

within on and off center surround environments; ganglion cells; communicate to bipolar cells - net output of convergence dictates whether cells become excited or inhibited

Question 28

retinofugal projection

Answer 28

flees eye
afferent projection - goes towards CNS

three components:

1) optic nerve
2) optic chiasm
3) optic tract

Question 29

decussation means

Answer 29

crossing over of info

Question 30

types of visual fields

Answer 30

temporal and nasal hemifields - nasal is the part closest to nose, temporal is part closest to outside; for both right and left eye

Question 31

if cut optic tract what would happen

Answer 31

lose half of vision on opposite side
left tract - right half vision
right tract - left half vision

Question 32

if cut optic nerve what would happen

Answer 32

lose 1/4 vision, only vision that isn’t covered by another part of the eyes

Question 33

cut optic chiasm what would happen

Answer 33

lose outside vision - sill have middle vision- no vision can cross over to be processed by correct part of brain

Question 34

visual pathway generally

Answer 34

retina–> LGN –> optic radiation –> primary visual cortex (area 17)

Question 35

what happens if you cut and damafe one side of thalaus and cover one part of eye

Answer 35

link to fear and stress gone - cat could see snake with one working eye and be scared. Cover that one up and use other working eye to see snake - now not scared

Question 36

superior colliculus function

Answer 36

important for eye movement

-

Question 37

____ % of info that comes from eye goes to superior colliculus through _____

Answer 37

10% via retinal tectum projection

Question 38

Lateral Geniculate Nucleus

Answer 38

located in thalamus

• 6 curved layers (geniculatus) going from bottom up
• first two layers are magnocellular - stain heavily with nissel staining- parvo cells are III to VI (alternating and starting at layer III with ipsilateral)- input comes from retinal ganglion cells - from contralateral visual field (not contralateral eye); not true that left visual field goes to left eye and right visual field goes to right eye –> crossing over
• output to striate cortex