Vision

Question 1

What is photoreception?

Answer 1

The ability to detect a portion of the electromagnetic spectrum between UV and IR.

Question 2

What is the minimal criteria to be considred an eye?

Answer 2

• Photoreceptors
• Determine directionality of light

Question 3

Despite the minimal criteria to be an eye, they are usually a complex organ and…

Answer 3

• include receptor cells
• pigmented epithelium

Question 4

Where are flat sheet eyes seen?

Answer 4

In larval eyes or as accessory eyes.

Question 5

Describe cup shaped eyes.

Answer 5

Curved eye creates a narrow aprture (allows less light into the eye)

Question 7

Describe convex eyes.

Answer 7

Present in annelids, molluscs and arthropodia.

Question 8

What are compound eyes composed of?

Answer 8

Ommatidia

Question 9

What are ommatidia?

Answer 9

• modified region of cuticle (cornea) overlying a crystalline cone that forms a lens
• below lens, retinular cells (rhabdomeric cell receptors)

Question 11

What are vesticluar eyes?

Answer 11

A lens help solve the compromise between image clarity and image intensity.

Question 12

List the structures related to function in the vertebrate eye.

Answer 12

• Sclera
• Cornea
• Iris
• Ciliary body
• Lens
• Fovea
• blindspot

Question 13

What does the vertebrate retina look like?

Answer 13

Question 14

What are the two types of photoreceptors?

Answer 14

Ciliary and Rhabdomeric

Question 15

What do photoreceptors do?

Answer 15

Transduce light signal

Question 16

Describe ciliary photoreceptors.

Answer 16

Single cilium with highly-folded ciliary membrane (disks containing photopigments). Vertebrates.

Question 17

Describe rhabdomeric photoreceptors.

Answer 17

Microvillar - projections contain photopigments. Jellyfish, drosophila.

Question 18

Describe signalling in rhabdomeric photoreceptors.

Answer 18

• G_q protein activates PLC pathway
• IP3 and DAG pathways open nonselective cation channels
• Ca²⁺ and Na⁺ enter the cell
• Cause a depolarizing receptor potential
• NT release is increased

Question 19

What are the two types of photoreceptors in vertebrates?

Answer 19

Rods and cones

Question 20

What is a photopigment?

Answer 20

Chromophore associated with specific receptor protein.

Question 21

How are the chromophore and receptor protein binded?

Answer 21

Covalently

Question 22

Receptor proteins in photopigments are…

Answer 22

GPCR and members of the opsin family

Question 23

Give an example of a photopigment.

Answer 23

Retinal + opsin = rhodopsin

Question 24

Describe

Question 25

Describe the unactivated state of rhodopsin.

Answer 25

• chromophore in cis conformation
• bound to opsin

Question 26

Describe the activated state of rhodopsin.

Answer 26

* chromophore undergoes conformational change to trans * released from opsin (process called bleaching) * recycled (trans --\> cis) in the RPE

Question 27

What enzyme reverses the isomerization of retinal?

Answer 27

Isomerase

Question 28

Describe ciliary photoreceptor transduction.

Answer 28

Question 29

What does bright light cause?

Answer 29

* Lowest levels of cGMP * Most Na⁺ channels

Question 30

What happens to photoreceptors in the dark?

Answer 30

* cGMP levels are high; cGMP binds to ion channels * depolarization is triggered

Question 31

What happens to photoreceptors in dim light?

Answer 31

* lower levels of cGMP present * some ion channels close

Question 32

Show rhodopsin inactivation.

Answer 32

Question 33

Describe how the use of glutamate (inhibitory NT) is utilized in darkness and in light by photoreceptor cells.

Answer 33

Question 34

How do vertebrates recycle chromophores?

Answer 34

* released trans form exported to adjacent epithelial cells * converted back to cis form * exported back to photoreceptor cells

Question 35

Horizontal cells ensure...

Answer 35

that only signal from intensely lit photoreceptor cells reaches the ganglion (lateral inhibition).

Question 36

How do horizontal cells inhibit the activity of the bipoalr neurons connected to the photoreceptors at the center of the receptive field?

Answer 36

Photoreceptors synapse with bipolar neurons and with horizontal cells. Conflicting signals to these bipolar neurons ersults in reduced signal to retinal ganglion cells.

Question 37

Show the difference between light on the centre of the receptive field and light on surround.

Answer 37

Question 38

What is the pathway of APs from the retina to the brain?

Answer 38

Optic nerves --\> optic chiasm --\> optic tract --\> lateral geniculate nucleus --\> visual cortex

Question 39

Describe binocular vision.

Answer 39

* eyes have overlapping visual fields * binocular zone * combine and compare information from each eye to form a 3D image * depth perception