eye and phototransduction Flashcards
briefly dscribe the evolution of the eye and visual activity
region of photosensitive cells -> depressed folded areas for directional sensitivity -> pinhole eye -> transparent humor in enclosed chamber -> distinct lens -> iris and cornea
what is visual acuity
measure of ability to distinguish 2 nearby points = dependent on density of photoreeptor packing
waht are some functions of photons other than visual processing
saccadic eye mvm, coordinating visual, somatic and auditory info, ajudtig mvm of head and eyes towards a stimulus
describe the pathway of light to reaech photoreceptors
travle across transparent retina (displaced portion of the CNS) before reached photoreeptor layer
why is the location of photoreceptor layer importnat
high regeneration and metabolic needs and need to be near blood
what are the 2 types of photoreceptors
rods = detect amount of light cones = perception of colour
describe the outer segment, innter segment and terminal of rods and cones
outer = region of phototransduction = falttened organelles. rods = membrane disks and cones have infolding
inner segment = nucleus and mitochondria
terminal = connected by axon-like process
what is scotopic and photopic vision
scotopic = night photopic = day
rod or cones are better with sptial and temporal resolution
cones are better
rods can detect dim lights tho
what is the fovea and is its structure
pinhead sized depression where cells other than cones are pushed out the way
high resolution = 1:1 ratio b/cones and ganglion cells
what are the 3 elements of the periphery
1 - higher ratio of rods to cones
2 - convergence of more photoreceptors
3 - more sensitive to light (night vision)
what is rhodopsin
light receptor molecule GPCR tightly packed in disk membranes and absorbes photons. there aew 10 billion rhodopsin molecules in a single rod
what are the 2 components of rhodopsin
retinal = deriviative of vit A opsin = polypeptide with 7 transdoms
what happens when the all trans isomer of retinal activates opsin
opsin signals to heterotrimeric g protein transducing and intiriates 2nd messenger cgmp cascade
1 opsin can activate waht ….
enough signal amplification that 1 photon can produce 1 mV hyperpolarisaiton
opsin can activate …
enough signal amplification so that 1 photon produce 1mv hyperpolarisation
what are the 3 types of cones
short = blue
medium = green
long = red
they ahve varying opsins
what is colour [erception derived from
the overlapping but distinct responses
what does the absorption of light by 11-cis retinal cause
a rotation around the doube bond to form more stable all trans retinal and a confromational change in the opsin
what does variation of opsin in rodsdo
permits variation of spectral activity
what can lead to colourblindness
recombination = hybrid/loss/duplcation of genes
describe mechanism of the dark current
inwardly directed NA and outward K+ for depolarisation and darkness
what happens to polarisation in light
photos close cation channels but K remains open = hyperpolarisation = light
describe the info flow of neurons in the retina
photoreceptors (rods + cones) -> bipolar cells -> retinal ganglion cells
what types of interneurons are there in the retina and what are they for
horizontal and amacrine cells for lateral interactions
waht is the computational task of the retina
= to form sensitive and economical neural representation of the light image
what preserves connections in photoreceptors
electrical or glutamatergic synapses
what causes sign-inverting connections
gabaergic, glycinergic or glutamatergic synapses
how do rods feed into the circuitary
via A2 amacrine cells
