Sensory Systems - The Eye

Question 1

What two forms can light be described as?

Answer 1

Electromagnetic wave and photons

Question 2

What determines the intensity of light?

Answer 2

Amplitude = intensity of light

Question 3

What determines the color of light?

Answer 3

Wavelength = distance between peaks

Question 4

What is the primary refracting component of the vertebrate eye?

Answer 4

Cornea
It has a fixed position & shape

Question 5

What is myopia?

Answer 5

Short-sightedness
Caused when lens is too strong & focal point happens too soon

Corrected by concave lenses which spread out the waves of light

Question 6

What is hyperopia?

Answer 6

Far-sightedness
Caused by a weak lens & focal point occurs beyond the retina

Corrected by convex lenses which focus light before it reaches the lens

Question 7

What type of lens corrects myopia?

Answer 7

Concave lens

Question 8

What type of lens corrects hyperopia?

Answer 8

Convex lens

Question 9

What is the function of the retinal pigment epithelium?

Answer 9

Pigment layer at the back of the retina (make pupils look black)
Essential for recycling of retinaldehyde (light-sensing protein) thus maintaining function of rods & cones
Helps rods & cones to cope with oxidative stress (caused as a byproduct of rods & cones activity)

Question 10

What are the two types of photoreceptors in the retina?

Answer 10

Rods and cones

Question 11

What is the role of rods?

Answer 11

Night vision and peripheral vision

Question 12

What is the role of cones?

Answer 12

Color vision and visual acuity

Question 13

What is unique about the arrangement of the retina?

Answer 13

Retina is ‘inside-out’ = light goes through several layers of retinal cells before it reaches the photoreceptors

Question 14

What is phototransduction?

Answer 14

Process by which photoreceptors convert light into electrical signals

Question 15

What is opsin?

Answer 15

GPCR with 7 transmembrane domains
Different opsins in 3 types of cones (sensitive to red, green & blue light), rods and melanopsin (in retinal ganglion cells)
RGCs = 5 opsins

Question 16

What vitamin derivative is involved in phototransduction?

Answer 16

Retinal

Question 17

What happens to photoreceptors in the presence of light?

Answer 17

Hyperpolarization occurs
Light causes Na+ channels to close

Question 18

How many types of cones do humans have?

Answer 18

3 types

Question 19

How many types of cones do mantis shrimps have?

Answer 19

12-16 types

Question 20

What is the significance of the fovea?

Answer 20

Area of maximum visual acuity

Question 21

Fill in the blank: The _______ layer is just behind the retinal pigment epithelium.

Answer 21

Tapetum lucidum

Question 22

What is the role of bipolar cells in the retina?

Answer 22

Transmit signals from photoreceptors to ganglion cells

Question 23

What are intrinsically photosensitive retinal ganglion cells (ipRGC)?

Answer 23

RGCs that can detect light via melanopsin

Question 24

What does melanopsin affect?

Answer 24

Circadian rhythms, pupil size, and body temperature
By responding to light intensity (subconsciously)

Question 25

What is the visual pathway responsible for?

Answer 25

Conscious visual perception

Question 26

What is the primary area in the brain for processing visual information?

Answer 26

V1, striate cortex - located in the occipital lobe This has orientation selectivity = cell only produces a response when light is in a specific direction

Question 27

True or False: Retinal cells provide early processing of visual information.

Answer 27

True

Question 28

What do horizontal cells in the retina assist with?

Answer 28

Light intensity adaptation and color processing

Question 29

What is the significance of the lateral geniculate nucleus (LGN)?

Answer 29

Processes conscious visual information before it reaches V1

Question 30

What is a common vision-related disorder associated with the structure of the eye?

Answer 30

Astigmatism

Question 31

Fill in the blank: Rods are _______ times more sensitive than cones.

Answer 31

1000

Question 32

Structure of the vertebrate eye

Answer 32

- Lens = 12 D (ability to bend light) - Cornea = 42 D - Optic nerve = goes from eye to the brain - Retina = part of the CNS

Question 33

What is the role of the lens?

Answer 33

Accommodates by changing shape for more refractive power

Question 34

Structure of the retina

Answer 34

- Retinal ganglion cells (spikes to the brain) - Amacrine cells (intermediate) - Bipolar cells - Horizontal cells (intermediate) - Rods & cones Light travels from retinal ganglion cells to the rods & cones and visual information travels the opposite direction

Question 35

What are cones characterised by?

Answer 35

Responsible for daytime vision and allow us to see in colour Located in the fovea where we have max visual acuity This area is blind at night

Question 36

What are Rods characterised by?

Answer 36

Responsible for night vision & peripheral vision 1000x more sensitive than cones Properties of rods means that we are poorer at discriminating colour in the periphery and at night

Question 37

What forms photopigment?

Answer 37

Opsin + retinal

Question 38

What is retinal?

Answer 38

Vitamin A derivative Same for every opsin Absorbs light and changes conformation = bleaching (seeing big white dot after looking at a bright light) where another photon can’t be absorbed

Question 39

What happens to photoreceptors in the dark?

Answer 39

Na+ channels open They depolarise = activate in the dark

Question 40

Describe phototransduction in rods and cones

Answer 40

Retinal absorbs light and changes conformation, results in closure of Na+ channels & hyperpolarisation - Photon of light causes conformational change in rhodopsin molecule - Activation of transducin via GDP exchange for GTP - Activation of phosphodiesterase - Reduction in cGMP - Closure of Na+ channels

Question 41

How do we see colour?

Answer 41

Cones need to be differentially activated for the brain to create the perception of colour

Question 42

Colour blindness

Answer 42

X chromosome contains red and green opsins so males are more likely to be colourblind Chromosome 7 contains the blue opsin

Question 43

Statistics of colour blindness

Answer 43

6% of men = anomalies in colour vision 2% of men = red/green colourblind 1% of women = anomalies in colour vision <0.001% of people = lack all colour vision Some women are tetrachromats (have 4 cones) due to 2 red alleles

Question 44

Role of horizontal cells

Answer 44

- Tunes information coming from the photoreceptor cells - Light intensity adaptation - Spatial processing - Colour processing (opponency)

Question 45

Role of amacrine cells

Answer 45

- Directional motion - Modulate light adaption - Modulate circadian rhythm - Sensitivity of night vision

Question 46

Role of retinal ganglion cells (RGCs)

Answer 46

- Further process colour, motion and shapes - The ONLY output cells of the retina, fire action potentials - Some can detect light via melanopsin = ipRGC (intrinsically photosensitive retinal ganglion cells)