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Lecture

CSB332H1 Lecture Notes - Stephen Kuffler, Ganglion Cell, Ganglion


Department
Cell and Systems Biology
Course Code
CSB332H1
Professor
Melanie Woodin

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CSB332H1S L22; Apr. 04, 2012
Sensory Systems
What is significance of bipolar cell RFs?
D & H bipolars not only responding to light
Begin to analyze info about light patterns
Tell the CNS about small spots of light surrounded by dark (& vice
versa)
Essentially responding to contrasting patterns of light & dark over
small patch of retina
“On” and “Off” Ganglion Cells
APs evoked in “on” ganglion cells by small spots of light shone
onto center of field surrounded by darkness
APs evoked in “off” ganglion cells by small dark spots surrounded
by light
Receptive Fields
RFs of ganglions 1st characterized by Stephen Kuffler in 1950s
Eyes of anesthetized cat focused on screen w various patterns of
light generated by computer
Electrode records responses from single cell in visual pathway
RF for ganglion determined by correlating area of screen
illuminated w neuron’s firing
Ganglion Cell Receptive Fields
Ganglions normally fire APs even at rest
RF mapped by correlating light shone on retina w increases or
decreases in AP firing of ganglion
2 main grps of ganglions: “ON” & “OFF” centre fields
“ON” centre cells respond best to spot of light shone onto central part
of RF; illumination of surrounding area firing of APs
Illumination of entire RF elicits weak discharges because centre &
surround cancel each other out
Receptive Fields
+ = if shine light, increase act
pot firing
Respond to changes in
contrast
“OFF” centre cells firing of
APs when central area of RF
illuminated & when light
turned off
Light shone onto surround of
“OFF” centre RF excitation of
neuron
Sizes of Receptive Fields
Neighbouring RFs collect info from similar but not identical areas
of retina
Small spot of light (0.1 mm) activate RFs of many ganglions
Throughout visual system: Neurons processing related info
clustered together
Size of ganglion RF depends on location in retina
o Ganglions in centre have much smaller RFs than those in
periphery
o Smallest in fovea
Ganglion Cell Types
2 main grps; project to dif regions of LGN:
1. P parvocellular
o Smaller
o Small RFs
o Respond to colour & fine detail
2. M - magnocellular
o Large
o Large RFs
o Respond well to movement
What Info do ganglion cells convey?
Photorecs ~ light meters
o Ganglions ignore much of this info from photorecs
o Ganglions don’t convey info about absolute levels of illumination
Ganglion cells measure difs in their RFs by comparing degrees of
illumination btwn centre & surround
F’nal Layers of the LGN
LGN is a way-station where ganglion axons sorted nearby cells
receive inputs from same region of visual field
o Neurons processing like info are clustered
Prime example of anatomical basis for parallel processing of info
LGN Visual Cortex
LGN axons project to primary visual cortex (V1)
o form retinotopic map
RFs of cortical cells don’t have centre-surround organization
o Consist of lines or edges
Adds additional level of visual analysis
6 layers of V1- specific organizational properties
o Each vertical stack of cortical cells fns as a module, taking
input from 1 location in visual space & forwarding processed
info to 2ndary visual areas
create model of visual field
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