Vision

Question 1

Where is the vitreous humour?

Answer 1

Behind the lens

Question 2

What is the vitreous humour?

Answer 2

Jelly like substance

Necessary for structural stability

Question 3

Where is aqueous humour?

Answer 3

Behind the cornea

Question 4

What does the aqueous humour do?

Answer 4

Deliver nutrients to the cornea

Question 5

Where is aqueous humour made?

Answer 5

Posterior chamber (behind the iris)

Question 6

Where is aqueous humour reabsorbed?

Answer 6

Anterior chamber

Question 7

Where does refraction occur?

Answer 7

Cornea

Lens

Question 8

What is accommodation?

Answer 8

Adjusting the thickness of the lens

Question 9

What controls the thickness of the lens?

Answer 9

The ciliary muscles

Question 10

What connects the lens to the ciliary muscle?

Answer 10

Zonule fibres

Question 11

How does the lens thicken?

Answer 11

Ciliary muscle constricts
Zonule fibres relax
Lens has natural elasticity

Question 12

When does the lens thicken or thin?

Answer 12

Near objects = thin

Far objects = thicken

Question 13

How does the lens thin?

Answer 13

Ciliary muscle relaxes
Zonule fibres tense
Lens thinned

Question 14

What nervous system controls the muscles of the eye?

Answer 14

The autonomic nervous system

Question 15

Besides the ciliary muscle, where else are there muscles in the eye?

Answer 15

Around the pupil

Question 16

Name the two types of photoreceptor

Answer 16

Rods

Cones

Question 17

What connects the cells of the retina?

Answer 17

Chemical synapses

Question 18

What generates action potentials in the eye?

Answer 18

Ganglion cells

Question 19

What allows lateral transmission?

Answer 19

Horizontal cells

Amacrine cells

Question 20

Name the three structural parts of photoreceptors

Answer 20

Outer segment
Inner segment
Synaptic terminals

Question 21

Where are photopigments located?

Answer 21

Outer segment

Question 22

What is the name of the photopigment in rods?

Answer 22

Rhodopsin

Question 23

What are photopigments specific to?

Answer 23

Wavelength of light

Question 24

Where is rhodopsin found?

Answer 24

Intracellular disks

Question 25

How sensitive are rods? Why?

Answer 25

Very High density of intracellular disks High levels of rhodopsin High surface area

Question 26

How many photopigments are there in cones?

Answer 26

3

Question 27

What are the three photopigments in cones?

Answer 27

Red opsin Blue opsin Green opsin

Question 28

Where are the opsins found?

Answer 28

Infoldings of surface membrane

Question 29

How sensitive are cones? Why?

Answer 29

Not very Low surface area Low levels of opsins

Question 30

Which photoreceptor is responsible for colour vision?

Answer 30

Cones

Question 31

What is the blind spot?

Answer 31

Where neurones enter the fovea and there are no photoreceptors

Question 32

Explain the distribution of cones and rods across the retina

Answer 32

``` Fovea = all cones Periphery = majority rods ```

Question 33

Is the periphery sensitive?

Answer 33

Very High number of rods Rods are very sensitive A lot of convergence of rods to ganglion cells

Question 34

What is low visual acuity? Why is there low visual acuity at the periphery?

Answer 34

Low clarity of vision | Convergence of rods means detail is lost

Question 35

What is the macula?

Answer 35

The centre of the retina

Question 36

How sensitive is the fovea?

Answer 36

Not very Low sensitivity of cones 1 cone: 1 gangion cell

Question 37

What happens to other cells in the fovea?

Answer 37

Lateral displacement | Allows as much light as possible to reach photoreceptors

Question 38

What is high acuity? Why is there high acuity at the fovea?

Answer 38

High clarity of vision 1 cone: 1 ganglion Many separate signals Detail not lost

Question 39

What is rhodopsin made up of?

Answer 39

Retinal (chromophore) | Opsin (G protein coupled receptor)

Question 40

In the dark, what is happening in a rod cell?

Answer 40

Rhodopsin is inactive cyclicGMP-gated cation channels are open Na+ enters the rod cell

Question 41

What is the flow of Na+ called?

Answer 41

The dark current

Question 42

What is the resting membrane potential of a rod cell in the dark?

Answer 42

-30mV

Question 43

Is the cell depolarised in the dark?

Answer 43

Yes

Question 44

What happens at the synapse in the dark?

Answer 44

Glutamate is released

Question 45

When light hits a rod cell, what absorbs the light?

Answer 45

Retinal

Question 46

What conformation change happens to retinal?

Answer 46

Changes from 11-cis to all-trans

Question 47

What does the change in retinal trigger?

Answer 47

Opsin is activated

Question 48

What happens once optin is activated?

Answer 48

GTP binds to the G-protein

Question 49

What does the G-protein activate?

Answer 49

Phosphodiesterase

Question 50

What does phosphodiesterase do?

Answer 50

Breaks down cyclicGMP | Channel closes

Question 51

Why does the cell hyperpolarise?

Answer 51

The Na+ channels close | Leak channels for K+ remain open

Question 52

What happens at the synapse in the light?

Answer 52

Glutamate release stops

Question 53

What is the route of transmission through the retina?

Answer 53

Photoreceptor Bipolar cell Ganglion cell

Question 54

What do photoreceptors do in the light?

Answer 54

Hyperpolarise

Question 55

What are the two classifications of bipolar cells?

Answer 55

On | Off

Question 56

What do on bipolar cells do in the light and in the dark?

Answer 56

Depolarised by light In the dark the glutamate from the photoreceptor hyperpolarises them In the light the lack of glutamate depolarises them

Question 57

What do off bipolar cells do in the light and in the dark?

Answer 57

Hyperpolarised by light In the dark, glutamate depolarises them In the light, lack of glutamate hyperpolarises them

Question 58

What causes opposite actions of bipolar cells?

Answer 58

The receptors they possess

Question 59

Name the two classes of ganglion cell

Answer 59

On and off

Question 60

For both ganglion cells and bipolar cells. Summarise on and off

Answer 60

``` On = depolarised by light Off = hyperpolarised by light ```

Question 61

What is the receptive field?

Answer 61

The region of the retina that influences a bipolar or ganglion cell

Question 62

What are the two divisions of the receptive field?

Answer 62

Central part | Surround part

Question 63

What is in the central part?

Answer 63

Direct connections from photoreceptors

Question 64

What is the surround part?

Answer 64

Lateral transmission of information via either horizontal or amacrine cells

Question 65

What happens when light is present in the surround field?

Answer 65

The opposite electrical response in bipolar and ganglion cells

Question 66

Why is the input of the surround field necessary?

Answer 66

Helps create contrast in image