lecture 4 - visual overview Flashcards
what is the purpose of the visual cortex
processes visual information
what is the purpose of the lateral geniculate nucleus
relay centre between the retina and visual cortex
what does the ventral pathway tell us
what kind of stimulus
what does the dorsal pathway tell us
where the stimulus is
what is the role of the pupil
regulates the amount of light falling on the retina
what is the role of the lens
focuses the image on the fovea
what is the fovea
the part of the retina with the highest visual acuity (one connection for each neuron)
what is the structure of the retina from the light source inwards
ganglion cells
inner plexiform
amacrine cells
bipolar cells
horizontal cells
outer plexiform
photoreceptors
which cells in the retina are excitatory
ganglion
bipolar
photoreceptors
which cells in the retina are inhibitory
horizontal
amacrine
at which light conditions are rod cells activated
dim light
at which light conditions are cone cells activated
bright light
does hyperpolarisation or depolarisation occur in photoreceptors?
hyperpolarisation
does hyperpolarisation or depolarisation occur in bipolar cells
both, depends on which type
describe phototransduction
rhodopsin activated by light
stimulates transducin to become transducin GTP
alpha subunit activates phosphodiesterase which reduces cGMP levels
hyperpolarisation
where does phototransduction occur
photoreceptors
what happens to glutamate release when photoreceptors are hyperpolarised due to light
it is decreased
describe the main differences between ON and OFF bipolar cells
ON- depolarise with light, metabotrophic glutamate receptors
OFF- hyperpolarise with light- use AMPA receptors
where do ON bipolar cells send their projections to
lower IPL
where do OFF bipolar cells send their projections to
upper IPL
what does a receptive field mean
retinal ganglion cells will only fire APs when specific areas are illuminated
does phototransduction occur in the outer or inner segment of photoreceptors
outer
what is centre- surround organisation and where does it occur
where the 2 different regions of a cell(inner and outer) have opposite polarities
occurs in bipolar cells and ganglion cells
how does centre-surround organisation happen
direct photoreceptors(in middle) will activate bipolar cells
peripheral photoreceptors will active bipolar cells via horizontal cells
these horizontal cells reverse the signal as they are inhibitory
what is the difference in effect of receptive fields of ganglion cells and bipolar cells
ganglion cells generate action potentials
bipolar cells generate graded potentials
describe the firing of OFF ganglion cells
non when light hits centre
more when light hits edge
none when light hits both
describe the firing of ON ganglion cells
more when light hits centre
non when light hits edge
non when light hits both
what are the 2 types of ganglion cell
parvocellular
magnocellular
what are the key differences between parvocellular and magnocellular cells
P- small dendritic tree
M- large
P-respond to colour
M-respond to motion
P- produce APs
M- produce quick bursts of energy
P- low sensitivity
M- high sensitivity
