ELM14: Sensory systems, vision

Question 1

What are the two features of light?

Answer 1

Wavelength
Amplitude

Question 2

What is meant by the wavelength of light?

Answer 2

The colour

Question 3

What is meant by the amplitude of light?

Answer 3

Intensity

Question 4

What is the role of the lens?

Answer 4

To focus the light onto the retina
Changes shape

Question 5

What is the role of the cornea?

Answer 5

Refracts light into the eye
Bulk

Question 6

What are the aqueous and vitreous humour?

Answer 6

Fluid filled areas
Help eye maintain shape

Question 7

What occurs when you look at something far away?

Answer 7

Lens gets flatter

Question 8

What happens when you look at something close?

Answer 8

Lens gets fatter

Question 9

What is myopia?

Answer 9

Short sighted
Focal point is too far forwards
Concave lens used

Question 10

What is hyperopia?

Answer 10

Far sighted
Focal point is too far back
Convex lens is used

Question 11

What are some features of the retina?

Answer 11

Several layers of specialised neurons
Has rods and cones

Question 12

What is the retinal pigment epithelium?

Answer 12

Inside of sclera
Recycles retinaldehyde and helps rods and cones with oxidative stress

Question 13

Where are rods and cones?

Answer 13

In the fovea which has max visual acuity

Question 14

What are rods more useful for?

Answer 14

Night and peripheral vision
1000x more sensitive than cones

Question 15

What are cones useful for?

Answer 15

Distinguishing colour

Question 16

How are rods and cones different in terms of structure?

Answer 16

Similar apart from outer segments

Question 17

What is the structure of the outer segments in rods and cones?

Answer 17

Multi-layered segments
Lots of membranous discs

Question 18

What do the membranous discs in the outer segments of rods and cones contain?

Answer 18

Opsins

Question 19

What are opsins?

Answer 19

Proteins that form a photopigment when bound to retinaldehyde
Humans have 5 types

Question 20

Why do rods have a larger outer segment?

Answer 20

So they can contain more opsins and be more sensitive to light

Question 21

What is retinal?

Answer 21

Vitamin A derivative
Absorbs light and changes conformation
Pigment is bleached until retinal is reset In discs

Question 22

What is the role of rhodopsin?

Answer 22

Binds to retinal in discs and forms a photopigment

Question 23

What happens when photoreceptors are in the dark?

Answer 23

Sodium channels open
Photoreceptors are depolarised

Question 24

What happens when photoreceptors are in the light?

Answer 24

Sodium channels close
Hyperpolarisation

Question 25

What is the overall process of retinal becoming activated?

Answer 25

1. Absorbs light and changes conformation
   2.Sodium channels close
2. Hyperpolarisation

Question 26

What is the process of phototransduction?

Answer 26

1. Retinal absorbs light and becomes all trans retinal
2. Conformational change in rhodopsin
3. Transducin has change of GDP to GTP
4. Activates phosphodiesterase
5. Reduces cyclic GMP
6. Closure of sodium channels

Question 27

What are trichromats?

Answer 27

Humans
3 types of cones

Question 28

What are monochromats?

Answer 28

Whales and seals
1 type of cone

Question 29

What are dichromats?

Answer 29

Mice cats and horses
2 types of cone

Question 30

What type of opsins does the X chromosome have?

Answer 30

Red and green

Question 31

What kind of opsin does chromosome 7 have?

Answer 31

Blue

Question 32

What are the 3 other types of retinal cells?

Answer 32

Bipolar
Horizontal
Amacrine

Question 33

What are bipolar cells?

Answer 33

Relay cell between photoreceptor and retinal ganglion cell

Question 34

What are horizontal cells?

Answer 34

Light intensity adaptation
Spatial processing
Colour processing

Question 35

What are amacrine cells?

Answer 35

Directional motion
Modulate light adaptation
Modulate circadian rhythm
Sensitivity of night vision

Question 36

What are retinal ganglion cells?

Answer 36

Further process colour motion and shapes
Only output cells and fire APs
Detect light with melanopsin

Question 37

What is melanopsin?

Answer 37

Doesn’t help image formation
Affects circadian rhythms pupil size and body temperature