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Lecture 2

NROC64H3 Lecture Notes - Lecture 2: Amacrine Cell, Retina Horizontal Cell, Ganglion Cell


Department
Neuroscience
Course Code
NROC64H3
Professor
Matthias Niemeier
Lecture
2

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Lecture 2 Vision 2
Bipolar Cells
- Synapse with either rods or cones
o one group of bipolar cells receiving rod information and another receiving cone
information and passes on info to the ganglion cells
- Also synapse with horizontal cells
- Dendrites receive information from photoreceptors, and their axons transmit
information to the ganglion cells
o Can be direct or indirect (via amacrine cells)
Variety of types:
- Diffuse- receives input from up to 50 photoreceptors and pools it before passing it on to
single source
Characteristic of rod pathway
Better for visual sensitivity
- Midget- receives input from single source and passes it on to single source
o Characteristic of cone pathway
o Better for visual acuity
- Cones:
o RF that are non-uniform can be on or off
o Half cells in signal in light (ON)
o The other half cells convey signal when
there is in the light (OFF)
- Rods:
o all of the ON variety
- Photoreceptors release glutamate to talk to BP cells
- ON bipolar cell has mGluR6 receptors which is inhibitory
- OFF bipolar cells has AMPA which is excitatory
- In dark:
o Cones release glutamate
o ON bipolar cell is hyperpolarizes which causes no
neurotransmitter to be released - inhibitory
o OFF bipolar cell depolarizes which causes release
neurotransmitters to ganglion cell - excitatory
- In light:
o Cones hyperpolarizes so no glutamate is released because it is
becoming more negative
o ON bipolar cell depolarizes which causes release
neurotransmitters
o OFF bipolar cell (because no more glutamate) hyperpolarizes which causes no
neurotransmitter to be released
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- Flat bipolar cells: dendritic tips are on the surface of photoreceptor
o Mainly OFF variety
- Invaginating bipolar cells: dendritic tips penetrate the photoreceptor
o Mainly ON variety
Horizontal cells
- Help integrate and regulate the input from multiple photoreceptors
- Responsible for allowing eyes to adjust to see well under both bright and dim light
conditions.
- Provide inhibitory feedback to rod and cone photoreceptors
- In dark:
o Cones release glutamate
o Photoreceptors depolarize horizontal
cells which causes release of GABA
(inhibitory transmitter)
o Horizontal cells hyperpolarize
adjacent cone
- In light:
o Cones hyperpolarize so no
neurotransmitter released
o Hyperpolarizes horizontal cell so no
GABA is released
o Less inhibition of neighboring cone
Amacrine cells
- Rod bipolar cells synapse via these
- Mainly release inhibitory neurotransmitters
o Inhibit the cone OFF bipolar cells
o What happens in dim light trying to see what rods can see not what cones can
see
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Ganglion cells they are all excitatory
- Receives signals from bipolar and amacrine and sends signals via
optic nerve
- All types fire action potentials and are excitatory and depolarize
- Variety of types:
o Midget- receives signals from midget bipolar
70% of cells are this type
o Parasol- receives signals from diffuse bipolar (multiple
signals being pooled)
- Cells that receive signals from ON bipolar cells are also ON center
cells with an OFF surround
- Ones with OFF input are OFF center ON surround
- Most sensitive to differences in intensity of light in the center and surround
- Video on Ganglion Cells:
o Ganglion cell gets excited when light is on its centre
- Midget cells: receive signal from midget bipolar
o Smaller receptive fields
o Finer resolution under higher lighting conditions
o Respond with sustained firing constantly be firing
- Parasol cells:
o Larger receptive fields receiving info from multiple sources
can look over larger area
o More sensitive under low lighting conditions
o Respond with burst firing
Primary Visual Pathway
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find more resources at oneclass.com
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