Receptive fields and visual pathways Flashcards
how are on centre bipolar cells stimulated? How are they inhibited?
-stimulated by a decrease in glutamate from cones and rods and so are depolarised by increased luminance.
-inhibited by an increase in luminance from cones and rods and so are hyperpolarised by a decrease in luminance
what could you look at to trigger a strong response from on centre bipolar cells?
light images on dark backrounds
how are off centre bipolar cells stimulated and how are they inhibited?
-stimulated by an increase in glutamate from cones so are depolarised by reduction in luminance
-inhibited by decrease in glutamate from cones so are hyperpolarised by increase in luminance
what could you look at to trigger a strong response from off centre bipolar cells?
dark images on light backgrounds
What are the two types of cells in the fovea?
parasol cells and midgit cells
what are the 5 functions of horizontal cells?
-carry info horizontally across the retina in the outer plexiform layer
-feed information between bipolar cells
-feedback info to photoreceptors
-communicate with other horizontal cells through gap junctions
-receive feedback from inner plexiform layer
-shape receptive fields of bipolar cells
-send feedback to photoreceptors, modulating photoreceptor signal under different light levels
What are amacrine cells?
interneurons that carry info laterally through the inner plexiform layer and synapse with bipolars, amacrines and ganglion cells
what do amacrine cells do?
help sharpen up receptive fields of ganglion cells like horizontal cells do for bipolar cells
what is the definition of the receptive field of a cell that transmits visual signals
the area of the retina over which a light stimulus can change the activity of that cell
what is the dendritic field of a ganglion cell?
the physical area of the dendritic arbour
what is the receptive field of a ganglion cell
the area of photoreceptors that will ultimately contribute to the response of the ganglion cells
what is the significance of horizontal cells in terms of receptive field?
they add an opponent signal to the receptive field and introduce centre-surround antagonism
how does the configuration of the receptive field come about and what is it shaped as ?
- horizontal and amacrine cells contribute to the formation of receptive field configuration
- RF centres have a positive response to it’s preferred stimulus
- RF surrounds have a negative response to the same stimulus
- the positive and negative responses combine to give the Mexican hat configuration
what cell recieves centre surround organisation of bipolar cell RFs?
ganglion cells
what cells modify the RF of ganglion cells?
amacrine cells
how are on centre ganglion cells affected by the RF?
they respond strongly to light on the centre of the RF and dark on surround
how are off centre ganglion cells affected by the RF?
they respond strongly to dark ion centre of RF and light on surround
give three consequences of the centre-surround organisation
-centre-surround organisation manifests as spatial antagonism
-the visual system responds strongly to luminance boundaries and less strongly to even, unchanging areas of luminance
-ganglion cells are spatially tuned to spots of different sizes
how do ganglion cells show spatial tuning
they are size specific as in they respond most strongly to a stimulus of a specific size so any larger or smaller and the response is reduced
what are achromatic pathways?
these compare brightness of an image across the retina
what cones are responsible for achromatic pathway through the retina
L-cones and M-cones
what cones are responsible for colour pathways across the retina?
L, M and S cones
what are chromatic pathways
compare wavelength of light across the retina