The visual system: eye and retina

Question 1

How much of the neocortex is involved in analysing the visual world?

Answer 1

1/3

Question 2

What colour do short wavelengths in visible light appear?

Answer 2

Blue

Question 3

What is the wavelength?

Answer 3

Distance between peaks and throughs

Question 4

What is the frequency?

Answer 4

Number of waves per second

Question 5

What is the amplitude?

Answer 5

The difference between a wave peak and a trough

Question 6

What are optics?

Answer 6

Light interacting with the environment

Question 7

Why does refraction occur?

Answer 7

The speed of light differs between mediums

Question 8

Function of the pupil

Answer 8

Lets light inside the eye

Question 9

Function of the iris

Answer 9

Contains muscles which control the amount of light entering the eye

Question 10

Function of the cornea

Answer 10

Glassy transparent covering of the pupil and iris
-Refracts light and focuses towards the back of the eye
- Nerve endings which adapt over time

Question 11

Function of the sclera

Answer 11

Forms the tough, protective wall of the eyeball to give it shape

Question 12

Function of the extraocular muscles

Answer 12

Move the eyeball
Controlled by oculomotor nerve (cranial nerve 3)

Question 13

Function of the optic nerve

Answer 13

Carries axons from the retina to the brain
- Cranial nerve 3

Question 14

What type of animal has horizontal pupils?

Answer 14

Prey animals
- For wider vision

Question 15

What is the optic disk?

Answer 15

Origin of blood vessels and the optic nerve
- Cannot sense light

Question 16

What is the macula?

Answer 16

Region of the retina for central vision
- Devoid of large blood vessels to improve vision quality

Question 17

What is the fovea?

Answer 17

Thinnest section of the retina
- Area of highest visual acuity

Question 18

How does stretching of the lens occur?

Answer 18

Lens is suspended by zonal fibres (suspensory ligaments), attached to ciliary muscle, enabling stretching

Question 19

What is the degree of refraction determined by?

Answer 19

Difference in refractive indices between the two media
The angle at which light hits the interface between the two media

Question 20

Describe refraction by the cornea

Answer 20

Cornea is mainly water
- Light travels more slowly through water than air due to higher density so refraction occurs

Question 21

What is the focal distance?

Answer 21

Distance from refractive surface to convergence of parallel light rays

Question 22

What happens to the lens when objects are <7m away?

Answer 22

The lens fattens to provide additional refraction

Question 23

What is emmetropia?

Answer 23

Eye is in a normal state and can focus on the back of the retina

Question 24

What is hypertropia?

Answer 24

Eyeball is too short so near objects are focussed behind the retina due to lack of refraction

Question 25

How is hypertropia fixed?

Answer 25

With convex glasses

Question 26

What is myopia?

Answer 26

Eyeball is too long so near objects are focused before the retina

Question 27

How is myopia fixed?

Answer 27

Concave glasses

Question 28

What cells does light pass through before it reaches photoreceptors?

Answer 28

Ganglion and bipolar cells

Question 29

What are plexiform layers?

Answer 29

Regions where synaptic connections occur

Question 30

Function of a ganglion cell in the retina

Answer 30

Output from the retina - Produce action potentials

Question 31

Function of an amacrine cell

Answer 31

Modulates information transfer between ganglion and bipolar cells

Question 32

Function of bipolar cells in the retina

Answer 32

Connect photoreceptors to ganglion cells

Question 33

Function of horizontal cells

Answer 33

Modulate information transfer between photoreceptors and bipolar cells

Question 34

Function of a photoreceptor in the retina

Answer 34

Sensory transducers - Both rods and cones

Question 35

Describe the structure of a photoreceptor

Answer 35

Membranous disks that contain light-sensitive photopigments that absorb light

Question 36

Function of a rod

Answer 36

High sensitivity - Enable vision in low light

Question 37

Function of a cone

Answer 37

High resolution -Colour - Daylight photopic

Question 38

Structure of a rod

Answer 38

Greater number of disks than a cone Higher photopigment conc 100x more light sensitive than cones

Question 39

Structure of a cone

Answer 39

Fewer disks than rods

Question 40

Describe convergence, sensitivity and resolution in the central retina

Answer 40

Low convergence Low sensitivity High resolution

Question 41

Describe convergence, resolution and sensitivity in the peripheral retina

Answer 41

High convergence High sensitivity Low resolution

Question 42

What changes the polarity of bipolar cells ?

Answer 42

Glutamate release at the synapse