Vision: Transduction Flashcards
define phototransduction
conversion of light energy to an electrochemical response by the photoreceptors (cones and rods)
what part of the rods and cones contain photoreceptors?
the discs and lamellae in the outer segments
describe the structure of the rods and cones from the outer segment to the synaptic terminal
> outer segment > inner segment, containing organelles > nucleus > axon > synaptic terminal
what is each lamellae made of?
cell membrane with integrated visual pigment
what is the visual pigment in rod cells?
rhodopsins
what are the visual pigments in cone cells?
opsins S, M and L
what differs between visual pigments?
the spectral sensitivity
what forms the chromophore nesting in the opsin in rhodopsin?
vitamin a
what happens when light falls on 11-cis retinal in rhodopsin?
it isomerises to all trans retinal which cannot fit in the opsin so rhodopsin splits resulting in a bleaching of the visual purple
how does bleaching of the visual pigment result in phototransduction?
phototransduction cascade
what role doe vitamin a play in the visual pigment?
visual pigment regeneration
what is the effect on na channels from light acting on rhodopsin?
na channels close
what is the effect of na channels closing on the retinal cell?
closed na channels result in the hyperpolarisation of photoreceptor cell, this is transmitted by flux of calcium ions to the synapse with bipolar cells stimulating the retinal cell.
where must vitamin a come from?
the diet
what is the effect of vitamin a deficiency?
> night blindness
> conjunctiva and corneal epithelium will be abnormal
