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Retinal Physiology Vocabulary
Retinal Physiology Vocabulary
Receptive Field Spatial summation Temporal summation Convergent wiring Divergent wiring
Retinal Physiology: from perceptionsto spike trains to photon capture, an overview
Tartuferi 1887Tartuferi 1887
Ganglion cell layer Amacrine cells
Bipolar Cells
Horizontal Cells
Rod and Cone Photoreceptors
Key points to rememberKey points to remember
Duel photoreceptors system (rods & cones) extend the range of visual function.
The minimal direct pathway for a signal is photoreceptor to bipolar cell to ganglion cell.
Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtionlateral inhibtion and center-surround center-surround organizationorganization.
Duel photoreceptors system (rods & cones) extend the range of visual function.
The minimal direct pathway for a signal is photoreceptor to bipolar cell to ganglion cell.
Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtionlateral inhibtion and center-surround center-surround organizationorganization.
In foveate animals the overwhelming majority of visual behavior depends on this minute (<1%) patch of retina. (Tiny area of high spatial acuity).
Fast response time, but insensitive.
Wide range of adaptation (6+ Log Units)
In foveate animals the overwhelming majority of visual behavior depends on this minute (<1%) patch of retina. (Tiny area of high spatial acuity).
Fast response time, but insensitive.
Wide range of adaptation (6+ Log Units)
Light is the ligand that triggers activation of the enzyme.
Biochemistry of PhototransductionBiochemistry of Phototransduction
Rhodopsin is Rhodopsin is thethe classic example of a classic example of a G-protein coupled receptor. (ligand = G-protein coupled receptor. (ligand = photons)photons)
RODS: High gain means high sensitivity RODS: High gain means high sensitivity (But takes time to develop).(But takes time to develop).
CONES Smaller Responses , due to CONES Smaller Responses , due to lower sensitivity (low gain) are over lower sensitivity (low gain) are over faster resulting in higher . . . faster resulting in higher . . .
Rhodopsin is Rhodopsin is thethe classic example of a classic example of a G-protein coupled receptor. (ligand = G-protein coupled receptor. (ligand = photons)photons)
RODS: High gain means high sensitivity RODS: High gain means high sensitivity (But takes time to develop).(But takes time to develop).
CONES Smaller Responses , due to CONES Smaller Responses , due to lower sensitivity (low gain) are over lower sensitivity (low gain) are over faster resulting in higher . . . faster resulting in higher . . .
Photocurrent & Photovoltages Graded responses (no spikes)Photocurrent & Photovoltages Graded responses (no spikes)
Photoreceptors are partially depolarized Photoreceptors are partially depolarized in the dark (due to an influx of Nain the dark (due to an influx of Na++ and and CaCa2+2+ ions). ions).
Light shuts off the influx, thus the cells Light shuts off the influx, thus the cells hyperpolarize and . . . hyperpolarize and . . .
Neurotransmitter is released constantly Neurotransmitter is released constantly in the dark and this release is in the dark and this release is attenuated by light!!!! (GLUTAMATE)attenuated by light!!!! (GLUTAMATE)
Photoreceptors are partially depolarized Photoreceptors are partially depolarized in the dark (due to an influx of Nain the dark (due to an influx of Na++ and and CaCa2+2+ ions). ions).
Light shuts off the influx, thus the cells Light shuts off the influx, thus the cells hyperpolarize and . . . hyperpolarize and . . .
Neurotransmitter is released constantly Neurotransmitter is released constantly in the dark and this release is in the dark and this release is attenuated by light!!!! (GLUTAMATE)attenuated by light!!!! (GLUTAMATE)
Rod vs. Cone Kinetic & SensitivityRod vs. Cone Kinetic & Sensitivity
Themes of retinal circuitryThemes of retinal circuitry
Highest visual acuity and fidelity of Highest visual acuity and fidelity of signals carrying that message requires signals carrying that message requires requires a private line (Midget system).requires a private line (Midget system).
Highest visual acuity and fidelity of Highest visual acuity and fidelity of signals carrying that message requires signals carrying that message requires requires a private line (Midget system).requires a private line (Midget system).
Private LinePrivate Line DivergenceDivergence ConvergenceConvergence
Private LinePrivate Line DivergenceDivergence ConvergenceConvergence
Themes of retinal circuitry Themes of retinal circuitry
Horizontal Cells and Amacrine cells Horizontal Cells and Amacrine cells provide lateral pathways in the retina.provide lateral pathways in the retina.
Feedback and feed forward synaptic Feedback and feed forward synaptic interactions add flexibility and complexityinteractions add flexibility and complexity
Spatial filters (Lateral inhibition)Spatial filters (Lateral inhibition)Temporal filters (Directional selectivity)Temporal filters (Directional selectivity)Network gain control (light/dark Network gain control (light/dark
adaptation)adaptation)
Horizontal Cells and Amacrine cells Horizontal Cells and Amacrine cells provide lateral pathways in the retina.provide lateral pathways in the retina.
Feedback and feed forward synaptic Feedback and feed forward synaptic interactions add flexibility and complexityinteractions add flexibility and complexity
Spatial filters (Lateral inhibition)Spatial filters (Lateral inhibition)Temporal filters (Directional selectivity)Temporal filters (Directional selectivity)Network gain control (light/dark Network gain control (light/dark
adaptation)adaptation)
On and Off pathwaysOn and Off pathways
Divergent wiring - cone hyperpolarizes to lightDivergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different Same neurotransmitter changes, different
responses.(receptor biochemistry)responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON On bipolar: sign inverting feeds onto ON
ganglion cells (SPIKING INCREASES)ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off Off bipolar: sign conserving feeds onto Off
Divergent wiring - cone hyperpolarizes to lightDivergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different Same neurotransmitter changes, different
responses.(receptor biochemistry)responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON On bipolar: sign inverting feeds onto ON
ganglion cells (SPIKING INCREASES)ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off Off bipolar: sign conserving feeds onto Off
Building Receptive FieldsBuilding Receptive Fields
Center and surround organizationsCenter and surround organizations Begin at the bipolar cell level via horizontal Begin at the bipolar cell level via horizontal
cell lateral synapsescell lateral synapses More complex at the Ganglion cell via Amacrine More complex at the Ganglion cell via Amacrine
cell synapsescell synapses
On or Off responses (anatomical On or Off responses (anatomical correlation with sublaminae of IPL)correlation with sublaminae of IPL)
Center and surround organizationsCenter and surround organizations Begin at the bipolar cell level via horizontal Begin at the bipolar cell level via horizontal
cell lateral synapsescell lateral synapses More complex at the Ganglion cell via Amacrine More complex at the Ganglion cell via Amacrine
cell synapsescell synapses
On or Off responses (anatomical On or Off responses (anatomical correlation with sublaminae of IPL)correlation with sublaminae of IPL)
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Bipolar Cell morphology/physiolgyBipolar Cell morphology/physiolgy Rod vs. Cone Rod vs. Cone anatomical connection-inputanatomical connection-input Midget vs. diffuse Midget vs. diffuse receptive field sizereceptive field size On vs. Off On vs. Off
Physiological subtypePhysiological subtype With anatomical correlationsWith anatomical correlations
On : Middle element of invaginating synapseOn : Middle element of invaginating synapse On: output synapse in the inner half of IPLOn: output synapse in the inner half of IPL Off: Flat synapseOff: Flat synapse Off: output synapse in the OUTER half of IPLOff: output synapse in the OUTER half of IPL
Unique Blue cone bipolar (non-midget)Unique Blue cone bipolar (non-midget) High contrast gain at input synapsesHigh contrast gain at input synapses
Rod vs. Cone Rod vs. Cone anatomical connection-inputanatomical connection-input Midget vs. diffuse Midget vs. diffuse receptive field sizereceptive field size On vs. Off On vs. Off
Physiological subtypePhysiological subtype With anatomical correlationsWith anatomical correlations
On : Middle element of invaginating synapseOn : Middle element of invaginating synapse On: output synapse in the inner half of IPLOn: output synapse in the inner half of IPL Off: Flat synapseOff: Flat synapse Off: output synapse in the OUTER half of IPLOff: output synapse in the OUTER half of IPL
Unique Blue cone bipolar (non-midget)Unique Blue cone bipolar (non-midget) High contrast gain at input synapsesHigh contrast gain at input synapses
Several distinct Several distinct morphological types morphological types have been have been identified.identified.
Some match Some match physiological typesphysiological types