Physiology of Vision Flashcards
What are the lateral cells in the retina?
horizontal cells and amacrine cells
What is the function of horizontal cells?
receive input from photoreceptors and project to other photoreceptors and bipolar cells
What is the function of amacrine cells?
receive input from bipolar cells and project to ganglion cells, biopolar cells and otehr amacrine cels
What is transduction?
the conversion of electromagnetic radiation to neural signals
What are the 4 regiosn of photoreceptrs?
outer segment; inner segment; cell body and synpatic terminal
What is the resting membrane potenetial of photoreceptors as compared to other neurons?
depolarised
What happens to the membrane potenetial of photoreceptors in response to light?
hyperpolarises
What is the dark current?
constant flow of sodium through a cGMP channel that is open in the dark and closed in the light
What is the visual pigment in rods called?
rhodopsin
What is rhodopsin composed of?
retinal and opsin
What happens to retinal in the light?
changes from 11-cis-retinal to all-trans-retinal
How does the activation of retinal cause closure of cGMP channels?
activats transducin and a molecular casacade that decreases cGMP
What is the neurotransmitter in the retinal ganglion cells?
glutamate
What is visual acuity largely determined by?
photoreceptor spacing
What are the differences between the distribution of rods and cones?
more convergence in rod system which increases sensitivity whilst decreasing acuity
What are the 3 types of cone?
short-wave; middle-wave and long-wave cones
What type of glutamate receptor is foudn in OFF bipolar cells?
ionotropic
What type of glutatmate receptor is foudn in ON bipolar cells?
metabotropic
What is the difference between ON and OFF bipolar cells?
ON bipolar cells are activated light ON (less glutamate) whereas OFF bipolar cells are activated by light OFF
What is the function of lateral inhibition?
exaggerates the difference in stimulus intensity detected by adjacent neurons, aiding localisation
What is the function of centre-surround organisation?
emphasis contrast sharpening boundary between objects of different luminance
What ar ethe 2 types of retinal ganglion cell?
M-type ganglion cell and P-type
What is the difference between M-type and P-type ganglion cells?
M-type have much larger receptive fields, they conduct APs more rapdly and are more sensitive to low contrast stimuli. thye respond to stimulation of their RF centre with a burst of APs whereas P-type respond with a sustained discharge
What are the 2 typeso of colour opponency?
red vs green and blue vs yellow
What type of retinal ganglion cells are color-opponent cells?
P-type and nonM-nonP
How many layers does the lateral geniculate nucleus have?
6
What are the ventral layers of the LGN (1 and 2) called?
magnocellular LGN layers
What are the dorsal layers (3-6) of the LGN called?
parvocellular LGN layers
Where do nonM-nonP type retinal ganglion cells project in LGN?
konio-cellular layers– numerous tiny neurons just ventral to each layer
Where do magnocellular LGN neurons project to in the visual cortex?
layer IVCa
Where do parvocellular LGN neurons project to in the visual cortex?
layer IVCb
Where do koniocellulal LGN axons project to?
layers II and III
Where are the first binocular neurons found in the visual cortex?
in layer III
What is the competition hypothesis?
connections from the two eyes compete with each other in cortex
What is the function of direction selectivity of the striate cortex?
analysis of object motion
