16 - transduction - how we see

what are rods and cones

photoreceptors in the retina

what is fond in cell membrane of rods and cones

rhodopsin

cones

colour

rods

light

bleaching of visual pigment results in what

phototransduction cascade

phototransduction steps

photon of light hits rhodopsin - activates it - changes shape and breaks into ops in

visual pigment released

activated opsin still in cell membrane

activates transducin-GDP

changes into transducin GTP

transducin GTP acts on phsophodiesterase or PDE - activates it

activated PDE acts on cGMP turning it into GMP

GMP acts on Na+ channels

Na+ channel closes

closing of channel causes relative hyperpolarisation of photoreceptors cell

transmitted by flux of Ca2+ ions to synapse with bipolar;ar cell

stimulates retinal cell in optic nerve

how is visual pigment regenerated after phototransduction

11-cis retinal to all trans retinal

all-trans retinal diffuses outside photoreceptor cell

picked up by pigment epithelial cells underneath photoreceptor cell

ATP used up

conversation of all trans retinol to 11-cis retinol to 11-cis retinal

back to photoreceptor cell to reform rhodopsin

common vitamin A deficiency eye signs

Bitot's spot

corneal ulceration

corneal melting