How we see 2: transduction

Question 1

What is phototransduciton?

Answer 1

conversion of light energy to an electrochemical response to allow light waves to stimulate photoreceptor cells on the retina

Question 2

What are the photoreceptor cells?

Answer 2

rods and cones

Question 3

What do the phototransduced rods and cones need to activate?

Answer 3

optic nerve neurons

Question 4

What is each lamellae in the outer segment of rods and cones made up of?

Answer 4

cell membranes

Question 5

rods visual pigment - transmembrane protein

Answer 5

rhodopsin

Question 6

cones visual pigment - transmembrane protein

Answer 6

cone opsins - S,M,L

Question 7

What are the 2 components making up rhodopsin?

Answer 7

opsin and 11-cis retinal

Question 8

Describe what happens to 11-cis retinal when light hits it?

Answer 8

becomes all trans retinol which cannot fit into opsin and so rhodopsin splits leading to bleaching of visual purple

Question 9

How does bleaching of visual pigment result in phototransduction?

Answer 9

phototransduction cascade

Question 10

What role does vitamin A play in visual pigment?

Answer 10

Regeneration of visual pigment

Question 11

Are photoreceptor cells depolarised at rest?

Answer 11

yes - open sodium, calcium channels

Question 12

How does the depolarise state change when light hits?

Answer 12

channels close, hyperpolarise, AP

Question 13

Where is the vitamin A which regenerates the visual pigment from?

Answer 13

diet

Question 14

What can 11-cis-rol go on to form instead of 11-cis retinal?

Answer 14

retinyl esters - pigment epithelial cell

Question 15

How does Vitamin A deficiency affect the corneal epithelium and conjunctiva?

Answer 15

Vitamin A essential for healthy epithelium

Question 16

How will a condition affecting absorption lead to vitamin A deficiency?

Answer 16

most of vitamin A is from the diet

Question 17

What are bitots spots?

Answer 17

silver, foamy, triangle lesions indicating the early stages of vitamin A deficiency

Question 18

2 other eye signs of vitamin A deficiency

Answer 18

ulceration and melting