The eye Ch. 51

Question 1

Light path to retina

Answer 1

lens – vitreous humor –>retina (bounces off pigmented layer in retina)

Question 2

How many layers does the retina have?

Answer 2

9 (light pathway begins with pigmented layer)

Question 3

At central foveal region, inside layers

Answer 3

are NOT present to increase visual acuity

Question 4

Rods are useful in the

Answer 4

dark

Question 5

cones are useful in the

Answer 5

light

Question 6

Components of rods and cones (4)

Answer 6

1. outer segment
2. inner segment
3. nucleus
4. synaptic body

Question 7

Inner segment of cones and rods have

Answer 7

mitochondria (ATP needed to activate enzymes)

Question 8

Types of cones (3)

Answer 8

1. Red
2. Blue
3. Green

Question 9

Light sensitive chemical is located on

Answer 9

outer segment

Question 10

Outer segment contains

Answer 10

1000 discs

Question 11

Color pigments are located

Answer 11

on outer segment in disc membranes

Question 12

Inner segments contain

Answer 12

Organelles, cytoplasm, many mitochondria

Question 13

Synaptic body role

Answer 13

connects with neuronal cells: horizontal and bipolar cells

Question 14

Melanin role

Answer 14

Prevents light reflection through eyeball = enhances contrast for formation of precise image

albinism = bad vision

Question 15

Vitamin A is a precursor for

Answer 15

rhodopsin

Question 16

Retinal blood supply

Answer 16

central retinal artery via optic nerve

highly vascular tissue between retina and sclera

Question 17

Retinal detachment

Answer 17

retina detaches from pigment epithelium = fluid and blood collect between layers

Question 18

Rhodopsin location

Answer 18

outer segment of rod

Question 19

Once light energy is absorbed, what happens (photochemistry)

Answer 19

Rhodopsin begins to rapidly decompose due to photoactivation of electrons = changes from cis to trans form

Question 20

Photochemistry of vision

Answer 20

Revisit slide 5 and ninja nerd special senses video
https://www.youtube.com/watch?v=GKaFjw8N8zQ

Question 21

Vitamin A

Answer 21

precursor with isomerase to convert all-trans retinal to 11-cis retinold

Question 22

Low vitamin A levels can cause

Answer 22

night blindness

Question 23

Rod excitation is

Answer 23

Hyperpolarizing

Question 24

What causes hyperpolarization of rods?

Answer 24

Rhodopsin decomposes and membrane conduction decreases for sodium ions

Question 25

Sodium flows into rods in the

Answer 25

dark

Question 26

Sodium flows through ___ in rods

Answer 26

cGMP-gated channels

Question 27

In the light, what happens to sodium flow in rods?

Answer 27

cGMP channels close, stopping flow of sodium into rod

Question 28

What rodopsin is activated cGMP channels are

Answer 28

closed

Question 29

activated rodopsin stimulates

Answer 29

G-protein transducin

Question 30

transducin

Answer 30

activates cGMP phosphodiesterase

Question 31

cGMP phosphodiesterase breaks down

Answer 31

cGMP to 5'-cGMP. Reduced cGMP closes channels (-70mV)

Question 32

In the dark, sodium flows through cGMP gated channels and causes membrane potential to be

Answer 32

-40 mV

Question 33

Rod excitation cascade

Answer 33

1. photon (light) activates electron in 11-cis retinol --> metarhodopsin II 2. activated rhodopsin enzymatic function -->activates transducin 3.activates phosphodiesterase 4.hydrolyzes cGMP -->sodium channels close 5.Rhodopsin kinase -->inactivates metharhodopsin and cascade reverses (including opening sodium channels)

Question 34

Cones are more/less sensitive than rods

Answer 34

30-300 times less sensitive

Question 35

cones use ___ for activation

Answer 35

photopsins

Question 36

Long exposure to light leads to

Answer 36

retinal and opsins

Question 37

retinal is converted to

Answer 37

Vitamin A

Question 38

Long exposure to darkness results in (2)

Answer 38

1. retinal and opsin conversion to light-sensitive pigments 2. Vitamin A converted to light sensitive pigments

Question 39

Cones adapt after

Answer 39

a few minutes

Question 40

Rods adapt for

Answer 40

minutes to hours and show extreme sensitivity

Question 41

Mechanisms of light and dark adaptation beyond rod/cone adaptation (2)

Answer 41

1. pupil size 2. neuronal adaptation

Question 42

Color vision

Answer 42

Blue, green and red cones each absorb separate certain % of light nm Brain interprets these absorptions as color

Question 43

Red-green colorblindness occurs when

Answer 43

red or green cones are missing, X - linked

Question 44

Photoreptors are

Answer 44

rods and cones

Question 45

Rods and cones synapse on

Answer 45

horiztonal and bipolar cells

Question 46

Bipolar cells transmit signals

Answer 46

vertically

Question 47

Bipolar cells synapse on

Answer 47

Amnicrine and ganglion cells

Question 48

Amnicrine cells synapse on

Answer 48

1. bipolar to ganglion 2. horiztonally to inner plexiform from axons of bipolar cells

Question 49

Ganglion cells role

Answer 49

sent signals from retina to optic nerve of brain

Question 50

Foveal vision pathway

Answer 50

cones -->bipolar cells -->ganglion cells

Question 51

Peripheral retina pathway

Answer 51

rods -->bipolar cells -->amacrine cels --> ganglion cells

Question 52

Rods and cones release _____

Answer 52

glutamate when synapsing with bipolar cells

Question 53

amarcrine cells secreute

Answer 53

Inhibitory nuerotransmitters (usually) GABA, glycine, dopamine, acetylcholine, indolamine

Question 54

all retinal neurons except _____ transmit via_____

Answer 54

except ganglion cells transmit via electronic conduction

Question 55

Electronic conduction is

Answer 55

graded conduction of signal strength

Question 56

Output from horizontal cells is always

Answer 56

inhibitory lateral inhibition = stops the spread

Question 57

Lateral inhibition creates

Answer 57

contrast borders in image

Question 58

Amacrine cells respond to (2)

Answer 58

1. Change in illumination 2. movement of a spot - directionally sensitive

Question 59

How many rods converge on an optic nerve fiber?

Answer 59

Up to 200 = summation

Question 60

P ganglion cells

Answer 60

slower impulse, stimuli sustained, sensitive to color NOT sensitive to low contrast (not great in dark) "new" brain

Question 61

M ganglion cells

Answer 61

Large, faster impulse, not sensitive to color (black and white stimuli) "reptile". brain

Question 62

Ganglion cells receive signal from

Answer 62

bipolar cells (could be excitatory or inhibitory)

Question 63

How is color contrast created?

Answer 63

One ganglion can be stimulated by several or only a few cones some ganglion cells are excited by one type and inhibited by a second type