Input | Output | Function | Morphology | Array | Comp. Model | Location | subclass | Syn Receptor | Transmitters | Immunocytochemistry | Nomenclature
The human retina has 110-125 x 10^6 rods (Oesterberg)
Back to list of cells
- Postsynaptic connections (Input)
- The rod is a photoreceptor, so its main source of input is the
transduction of light.
- Horizontal Cells
- Presynaptic connections (Output) -Diagram
- Horizontal Cells
- Rod Bipolar
- Phototransduction cascade - the hypothesized series of steps required to transform photon absorption into the closing of channels. notes mostly from Dowling's 'Retina' and Hille's 'Ionic Channels of Excitable Membranes' (nice web image)
- Pre-absorption rhodopsin: retinal (R or R) or 11-cis-retinaldehyde
- see Dowling's 'Retina' page 199 for rhodopsin -> all-trans which includes metarhodopsin I & II, pararhodopsin and opsin.
- Post-absorption rhodopsin: (R* or Rh*) all-trans-retinaldehyde
- R* stimulates Transducin, a G-protein (G_T)
- This stimulation, or the act of stimulation, causes transducin to exchange a guanosine diphosphate (GDP) molecule for a gaunosine triphosphate (GTP) molecule.
- Transducine with GTP activates Phosphodiesterase (PDE)
- PDE changes cyclic GMP (cGMP) into an inactive for, GMP
- cGMP acts as a second messenger and opens channels, decreasing cGMP results in channels closing.
- Channels close making the cell hyperpolarize.
- Absolute threshold = about -4.4 log photopic trolands
- Saturation begins at about 2.9 log photopic trolands
- Hood's "Sensitivity to Light" page 5-30: "By about 2,000 scotopic td, the rod system is incapable of discriminating between two lights that differ in intensity by as much as a factor of 100." Contrasts on a 120 cd/m2 background are undetectable.
- Maximally sensitive to 500 nm wavelength.
- Spatial summation up to 1-2 degrees (graham & Bartlett, 1939)
- Temporal summation up to 100 msec (Graham & Margaria, 1935)
- Temporal integration ~300 ms
- As photopigment absorbs light it becomes ineffective or bleached. General formulas for modeling photopigment depletion are available.
- Perpetual glutamate release in the dark, but glutamate release decreases in the light..
- Responsible for the A-wave in the ERG.
- Outer edge of fovea: 1.0 micrometers
- Parafovea: 1.0-1.5 micrometers
- Perifovea: 1.5 micrometers
- Distant Periphery: 1.5-2.5 micrometers
- Outer Segment
- Inner Segment
- Spherule - Presynaptic structure
- Array characteristics
- Compartmental Model Characteristics
- Synapse types
- Synapse Receptors
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© 1995 Lance Hahn (email@example.com)