The eye

Question 1

Where does the optic nerve take action potentials?

Answer 1

To the visual cortex

Question 2

Where do the optic nerves develop from?

Answer 2

Optic cups of the embryonic diencephalon

Question 3

What are the 3 layers of the eye?

Answer 3

Fibrous
Vascular
Neural

Question 4

Where is the aqueous humour located?

Answer 4

Anterior segment

Question 5

Which nerve controls movement of the eyelids?

Answer 5

Facial nerve - VII

Question 6

Where is the lipid component of the tear film produced?

Answer 6

Tarsal gland of the eyelid

Question 7

What is the conjunctiva?

Answer 7

Mucous membrane covering the eyelids and front of the eye, except the cornea

Question 8

What do goblet cells in the conjunctiva produce?

Answer 8

Mucin component of the tear film

Question 9

What are the 7 muscles surrounding the eyeball?

Answer 9

1. Dorsal rectus
2. Lateral rectus
3. Ventral rectus
4. Medial rectus
5. Ventral oblique
6. Dorsal oblique
7. Retractor bulbi/oculi

Question 10

Where is the aqueous component of the tear film produced from?

Answer 10

3rd eyelid and an extra gland called the lacrimal gland

Question 11

What is the fucnction of the Descemets membrane in the fibrous tunic?

Answer 11

Last defence in the eyeball

Question 12

What happens when the endothelium of the eye is damaged?

Answer 12

Cells don’t replicate so they get increasingly thinner and spread

Question 13

Where is the vascular tunic located?

Answer 13

Sits between the fibrous tunic and neural layer in the caudal part of the eye.

Question 14

What makes up the anterior and posterior uvea?

Answer 14

Anterior = iris and ciliary body
Posterior = choroid

Question 15

What is the function of the iris?

Answer 15

Iris is a sphincter with constrictor and dilator muscles which alter the size of the pupil to vary the amount of light entering the eye

Question 16

What is the term for:
1) Constriction of the eye?
2) Dilation of the eye?
What control are they under?

Answer 16

1 = miosis = parasympathetic

2 = mydriasis = sympathetic

Question 17

What is the function of the choroid?

Answer 17

Provides blood supply to deep layers of retina

Question 18

Name the structure that reflects light back to the retina to give improved night vision?

Answer 18

Tapetum lucidum

Question 19

What is the function of the lens?

Answer 19

Refracts light, and can change depth of focus by accommodation (limited in veterinary species)

Question 20

What are the 4 main cell types that make up the retina?

Answer 20

1. Retinal pigment epithelium (RPE)
2. Photoreceptor cells (rods & cones)
3. Bipolar ganglion cells
4. Multipolar ganglion cells

Question 21

Describe the field of view in prey species?

Answer 21

Very wide vision

Blind spot at the front

Question 22

What determines the shape of the pupil?

Answer 22

Shape of constrictor muscles

Question 23

What is the name of the corners of the eyelids?

Answer 23

Canthi

Question 24

What are the 2 types of photo receptors? What do each allow you to see?

Answer 24

Rods = black and white
Cones = colour

Question 25

What is the name of the photopigment that rods and cones contain?

Answer 25

Rhodopsin

Question 26

What makes up the photo-pigment rhodopsin?

Answer 26

opsin (protein) + retinal (vitamin A)

Question 27

Which species cannot convert B-carotene into vitamin A?

Answer 27

Cats

Question 28

What % of a cat/dogs photo-receptors are rods/cones?

Answer 28

95% rods | 5% cones

Question 29

Which molecule keeps sodium channels open meaning the photoreceptors stay active and release glutamate?

Answer 29

Cyclic GMP

Question 30

When is cyclic GMP released?

Answer 30

In the darkness

Question 31

What are the 5 steps in signal transduction?

Answer 31

1. Light energy is “trapped” by cis-retinal and the molecule changes conformation 2. This causes the large opsin molecule to loose its “retinal” and become active 3. Active opsin causes the alpha subunit of transducin (a G-protein) to activate cGMP phosphodiesterase 4. Results in an elevation of GMP but a reduction of cGMP 5. Sodium channels close and the cell hyperpolarises

Question 32

What is released when photoreceptors are active?

Answer 32

Glutamate

Question 33

What are the effects of glutamate being excitatory or inhibitory?

Answer 33

There are on and off bipolar cells

Question 34

What are the 2 other types of retinal neurons, what are they involved in?

Answer 34

Horizontal cells and Amacrine cells | - involved in visual processing

Question 35

How does the monocular and binocular vision vary in carnivores vs herbivores?

Answer 35

``` Carnivores = restricted monocular, large central binocular Herbivores = wide monocular lateral field, narrow binocular area ```

Question 36

What is the name of the visual cortex in the brain, in which species is this large?

Answer 36

Tectum | - in birds

Question 37

What process is the thalamus involved in?

Answer 37

Sensory processing

Question 38

Through which part of the thalamus does the optic nerve pass?

Answer 38

lateral geniculate nucleus