Eye Transduction

Question 1

what is phototransduction?

Answer 1

the energy in lightwaves needed to stimulate photoreceptor cells on the retina.
it is defined as the conversion of light energy to an electrochemical response by photoreceptors

Question 2

what are photoreceptors?

what do they do?

Answer 2

rods - detect light

cones - detect colours

Question 3

how does bleaching of the visual pigment result in phototransduction?

Answer 3

phototransduction cascade - photon of light causes rhodopsin to break down which has cascade of reactions which leads to Na+ channel closing causing hyperpolarisation until it reaches the cell of the optic nerve where it becomes an action potential

Question 4

what role does vitamin A play in visual pigment?

Answer 4

visual pigment regeneration - in order to have enough 11-cis retinal you need a constant supply of Vitamin A through your diet which is stored in your liver.
if there is a limited supply then rods begin to suffer first as they get bleached and can’t reform - they will have night blindness

Question 5

what is the pathology of vitamin A deficiency?

Answer 5

• night blindness
• conjunctiva and corneal epithelium are abnormal as vitamin A is essential for healthy epithelium
• malnutrition
• malabsorption diseases like coeliac disease and sprue

Question 6

what are some signs of vitamin A deficiency that you may see in the eye?

Answer 6

• bitot’s spot in conjuctiva - first indication usually - triangular spot that is silvery and foamy
• corneal ulceration (green coloured dye shows extent of ulcer)
• severe cases there may be melted cornea which will lead to opacification of the cornea in the future

Question 7

what is lamella made up of?

Answer 7

cell membrane with integral protons or opsins sitting within them