This Glossary documents the paradigm shift in the neural sciences cataloged in the
accompanying texts, The
definitions provided here take precedence over other definitions in
the literature. For a broader glossary of all Biological and
medical terms (except those introduced here), the reader might look
Online Version ------- Printed Version
"Processes in Biological Vision" Biological Vison: A 21st Century Tutorial "Processes in Biological Hearing" Hearing: A 21st Century Paradigm "Processes in Biological Olfaction." "The Neuron & Neural System" (In Preparation)
definitions provided here take precedence over other definitions in
the literature. For a broader glossary of all Biological and
medical terms (except those introduced here), the reader might look
A more extensive, 60 page, copy of this Glossary may be downloaded in .pdf format.
Abduct-- Physiology. To draw away from the midline of the body or from an adjacent part or limb
Abscissa-Distance from the vertical axis in a two dimensional plot.
Absorption Spectra--The composite signature of a chemical under electromagnetic stimulation. It generally includes ultraviolet, visible, infrared and radio frequency components. The various signature elements associated with a material can be related to specific electronic, and mechanical, structures within the molecules. In the Retinoids, the relevant ultraviolet and visible signatures are:
~187 nm. = p-p * electronic transition associated with an isolated carbonyl group
~285 nm. =n -p* electronic transition associated with an isolated carbonyl group
~380 nm. =
~493 nm. = delocalization transition associated with the length of the monopolar conjugated chain. Frequently reported as near 502 nm in order to agree with the putative peak in the C.I.E. Scotopic Luminous Efficiency Function.
~342, 437, 532 or 625 = delocalization transition associated with the length of the dipolar resonant chain
Adduct-- Physiology. To draw inward toward the median axis of the body or toward an adjacent part or limb
Achromatic--Without hue; achromatic color--a color that does not elicit hue; achromatic point--point in a chromaticity diagram representing an achromatic stimulus (The Science of Color)
Actinism--The intrinsic property in radiation that produces photochemical activity. Generally refers to ionization as opposed to excitation.
Action spectra--(inconsistently defined in the literature) Rodieck (pg 264) says an Action Spectra is a plot against wavelength of the intensity of a monochromatic source that produces the same measured response.It generally relates to a spectra obtained by psychophysical experiment.
Acyl--a chemical group consisting of R-C=O with an open ligand on C
Acylation-A specific form of esterfication involving the open ligand of an Acyl group.
Addition--Used in the conventional mathematical sense;not used in the physiological sense of "the co-operation of subliminal effects in such a way that the total effect is supraliminal".
Airy Image-A term for the two dimensional spread function representing the illumination at the image plane of an optical system. Expanded in precision, especially aerial, photography to include the effects of optics, vibration and atmospherics on the overall image applied to the recording medium.
Afferent--Carrying inward to a central organ or section, as nerves that conduct impulses from the periphery of the body to the brain or spinal cord. See also efferent.
Aliquot--Mathematics. Of, relating to,or denoting an exact divisor or factor of a quantity, especially of an integer.
Alychne--"Without light"; a term used to describe an arbitrary situation on the C.I.E. Chromaticity Diagram where the axis y=0 is defined as having no luminance.
Amercine--Cajal introduced the name for "cells lacking an (obvious) axon" based primarily on histological observations of the times. He further delineated diffuse and stratified types. Diffuse exhibiting a vertical branching structure and the stratified exhibiting primarily a horizontal branching.
Amphiphile--A compound having a polar head (ionic) which tends to dissolve in water (hydrophilic) and a water insoluble (hydrophobic) organic tail.
Anadromous--A fish that lives in saltwater but spawns in freshwater. Typical of Salmonidae.
Anagenesis--A term used by Kuhne to describe the spontaneous association in vision of the visual chromophore with the substrate protein. It has generally been considered to be a exothermic reaction.
Analogous Circuit--A term used to describe an electronic circuit used to emulate the performance of a system that does not employ free electrons as a medium, i. e. hydraulic or mechanical systems. In this work, excited electrons bound within a crystalline structure are not considered free.
Anaxonal neuron--In morphology, a neuron that does not exhibit a clearly defined axon. Informally called an amercine neuron based on Cajal's original definition.
Anterior--Nearer the head in Zoology
Antidromic--In a direction counter to the normal signal flow in the nervous system
Aperture Stop--The physical diameter which limits the size of the cone of radiation which an optical system will accept from an axial point on the object. For off-axis points, the limiting aperture may be defined by more than one physical feature of the optical system.
Aphakia--The condition resulting from the removal of the lens in the human eye. Patients in this condition have reported a visual sensation at wavelengths of 310-360 nm.
Apical--Of, relating to, located at, or constituting an apex; top
Apo--combination form meaning "away from" or "separate"
Apposition Eye--Conventionally, a compound eye where the rhabdoms receive light only from their "own" corneal facets. See also Superposition Eye. The photoreceptors of the apposition eye are optically isolated from adjoining corneal facets. Some authors have extended the concept to include computational as well as optical forms.
ARMD-Age related macular degeneration.
Arrestin-A putative material in the glutamate cascade theory of photodetection that participates in terminating the cascade. A 48 kDa S-antigen.
Aspheric lens--A fundamentally spherical lens that has been intentionally deformed in order to offer optimal aberration correction. See also non-spherical lens
Astrocytes-The name used for cells in the central nervous system equivalent of Schwann cells in the peripheral neural system and associated with providing myelination to the axons of neurons.
Autonomous nervous system-The nerves controlling the involuntary functions of the body that do not ordinarily relate to consciousness. Usually involves neurons emanating from the hind brain or midbrain. Separate from the peripheral system that responds primarily to the cortex.
Auxochrome--A polar atom which is capable of existing in two adjacent states of covalency; usually oxygen or nitrogen, less frequently sulphur or phosphorus.
-carotene--One of the simplest member of the carotenoid family of natural dyes. It is a polyene with 22 conjugated methine groups terminated on each end by a -ionone group.
Basal --Of, relating to, located at, or forming a base.
Beer's Law--The absorption coefficient for light passing through a solution of a given salt in a non-absorbing solvent is proportional to the concentration. For base 10 logarithms, the law is written as I=Io10-cx where is known as the molar extinction coefficient, c is the concentration in moles per liter, and x is the thickness of the transmitting layer. When written in natural logarithms, the is replaced by , the molar absorption coefficient. Law does not apply to liquid crystalline materials. The coefficients are "average" values over the wavelength region determined by the filter width used. Law developed from Bouguer's Law and Lambert's Law.
Bi-exciton--An excitonic molecule formed by two excitons. See exciton.
Bifurcation--A dividing of a structure. When used to describe a signaling channel, it supports two separate interpretations. The subchannels within the structure may branch in order to go to two distinct terminals simultaneously, or some subchannels may be routed differently than others in order to serve individual destinations. Each optic nerve bifurcates twice in the process of terminating in the brain.
Binding Proteins--RBP, CRBP, CRABP, CRALBP, IRBP
Blindsight--A condition, usually a result of injury, where the animal is able to respond to objects in their visual field, yet remain unaware that they are seeing those objects, and are unable to recognize the objects.
BLM--Bilayer membrane. A frequent abbreviation for a cell membrane. Usually consisting of two liquid crystalline films consisting of phosphoglycerides with their hydrophobic surfaces facing each other and separated by a space as observed with an electron microscope. Frequently labeled a three-layer membrane in other literature because of the dark-light-dark appearance in the electron microscope.
Boltzman-Maxwell distribution law-A probabilistic description of the energy distribution of particles in a material without regard to the Pauli Exclusion Principle of quantum mechanics. For electrons, the more specific Fermi-Dirac distribution based n quantum mechanics must be used.. See Guttmann & Lyons (1981), pg. 10.
Brain--For purposes of this work, and lacking a better name, the portions of the total brain related to vision with the exception of the ocular globes. Generally, the brain contains the following enumerated sections related to vision:
|Spinal Cord||Cerebellum||Retinas||Brain Stem||Cerebral cortex|
|Parietal lobe (upper side lobes)|
|Hypothalmus||Temporal lobe (lower side lobes)|
|Midbrain||Occipital lobe (rear-Pri. Vis. Cor.)|
|Auxiliary Optical Nucleus|
Calyx--The outer collar of the cup formed at the distal end of the Inner Segment and used as an extrusion die in the formation of the disks of the Outer Segment. Archaic: The structure surrounding the cilia as they enter the photoreceptor cell adjacent to the cup at the distal end of the Inner Segment. See ciliary transport.
Cardinal Points--The six points defined in geometrical optics to define the performance of a given lens or lenses. The Focal Points, Principal Points and Nodal Points (which occur in pairs).
Calorimetry--Measurement of the amount of heat evolved or absorbed in a chemical reaction, change of state, or formation of a solution
Capsule-- structure associated with but external to the terminal structure of a sensory neuron
Carapace-- A hard bony or chitinous outer covering of the dorsal portion of the head and thorax of an animal.
Catabolism--The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy.
Cephalic eyes--eyes located on the head. As opposed to pallial eyes located on the mantle.
Cephalin--ethanolamine phosphoglyceride, also known as phosphatidyl ethanolamine.
cGMP-- Guanosine 3',5' cyclic monophosphate
Chief ray--The ray that enters the lens midway between the highest and lowest rays of an oblique beam is called the chief ray of the beam. In the absence of vignetting, the chief ray and the principal ray are identical.
Chiral --Of or relating to the structural characteristic of a molecule that makes it impossible to superimpose it on its mirror image
Chromogen--A molecule which may be considered a precursor to a chromophore.
Chromophore--A group of associated atoms which can exist in at least two states of energy, a ground state of relatively low energy and an excited state to which it may be raised by the absorption of light energy from a specified region of the radiation spectrum.
Chromophore, visual spectrum--An organic dye molecule which contains at least 2 polar atoms joined by a conjugated chain of (usually) carbon atoms with alternating double and single bonds, equal numbers of each, thus forming a resonance hybrid. The most important chromophoric systems are the Amidinium-ion, Carboxyl-ion and Amidic
CIE--International Committee on Illumination; responsible for standards in this area. Most well known for the CIE Chromaticity Diagram of 1931 (2 degree Standard Observer) and the CIE Photopic Observer Curve of 1931 (2 degree Standard Observer) and the CIE Scotopic Observer curve of 1951 (2 degree Standard Observer)
-cil---a combining form meaning "hair", particularly those of the eyelid
Ciliary transport--See Colax.
Gray, Dictionary of Biological Sciences
1. a row of hairs or bristles on arthropods
2. a vibrative organelle process found on many cells throughout the animal kingdom. Each cilium consists of nine pairs of peripheral filaments wrapped round a central pair, the whole embedded in a matrix.
3. pseudo-cilium a structure resembling a cilium in form but not in function.
Cisternae--The inner compartments of endoplasmic reticulum
Colax-- The structural element through which pseudo-cilia (aka: more precisely dendrites but also known as microtubules) exit the photoreceptor cell in the area of the junction between the Inner Segment and the Outer Segment. Also known as the ciliary collar, the ciliary stalk, the connecting stalk or the ciliary transport.
Color--consists of the characteristics of light other than spatial and temporal inhomogeneities; light being that aspect of radiant energy of which a human observer is aware through the visual sensations which arise from the stimulation of the retina of the eye. (The Science of Color)
Color Constancy-A concept used in neurophysiology to describe the apparent stability of the color of objects under changes in illumination. Actually related to the stabilizing action of the three separate adaptation amplifiers in the human visual system which support a stabilizing of the perceived response in spite of changes in the average level of excitation of individual spectral channels.
Color globules-Isolated compartments of chromophore material found within the cytosol of the cells of the RPE.
Comparator- A nominally analog differencing circuit, that may be operated in synchrony with a clock or asynchronously, incorporating sufficient gain to force the output signal into saturation. Such circuits are typically used to provide one or more of three indications, X>Y, X<Y or X=Y. By using multiple individual comparators in logic circuits, significant characterization of a large group of input signals can be provided.
Compound eye--The eye of most insects and some crustaceans, which is composed of many light-sensitive elements, each having its own refractive system and each forming a portion of an image.
Contralateral--Taking place or originating in a corresponding part on an opposite side
CSF--The cerebral-spinal fluid containing the brain and acting as the electrical ground plane for the neurons of the brain
Cyanopsin--A conceptual name synonymous with Rhodonine(5) in the liquid crystalline form and derived from its observed broadband color resulting from its anisotropic spectral absorption peak at 625 nm.
Cyclogeranyl ring--a carbon structure ring exhibiting two methane groups attached at position 1 and a third methane attached at position 3 with a single double bond between position 2 and 3. The variant has a ligand attachment point on the carbon at position 2.
Cyprinid fishes--Any of numerous often small freshwater fishes of the family Cyprinidae, which includes the minnows, carps, and shiners.
Cytology--The study of biological cells, generally at the level requiring an electron- microscope
Cytosol--Generally equated to cytoplasm, or to the free cytoplasm without considering any inclusions therein.
Dartnall's Nomogram--A curve resembling a parabola when plotted on a scale of log sensitivity as a function of the frequency (as opposed to wavelength) of light. It was proposed that all photoreceptors exhibited spectral absorption functions that could be represented by this curve when it was shifted along the frequency axis
Deuteranomaly--Form of anomalous trichromatism for which in a green-red mixture, more than a normal amount of green is required to match a spectral yellow. (The Science of Color)
Deuteranopia--Form of dichromatism in which red and green are confused, but luminosity curve is nearly normal. (The Science of Color)
Deuterostomia--That large class of bilaterally symmetrical animals generally characterized by a notochord located along the dorsal surface of the animal
Dichromatism--Vision for which mixtures of two, rather than the normal three, components are necessary and sufficient to match all colors. (The Science of Color)
Difference Spectra--The difference in optical density [log(1/transmittance)] of the pigment layer before and after a partial or complete bleaching of the pigment, the result being independent of any stable "impurities" present in the layer. See Wyszecki & Stiles pg 588 for the details.They caution; "The difference spectrum is not comparable, without careful qualifications, to spectral response curves". The subject of translation of the signal to the nervous system is not addressed in this formulation.
Digitonin--A non-ionic detergent (a digitalis glycoside) resembling cholesterol. It has a strong attraction for dye molecules.
Dimer--The result of combining two molecules of the same material to obtain a new molecule with twice the original number of carbon and hydrogen atoms.
Diode--An electrical element exhibiting an exponential relationship between its current and voltage. Used in two applications depending on the value of the coefficient in the argument of the exponent. For a large coefficient, the device makes an excellent rectifier. For a small coefficient, the device is used in high accuracy signal processing applications.
Diopter--A measure of the optical image forming power of a lens and equal to the index of refraction of the medium in which the image is formed multiplied by the reciprocal of the focal length of the lens expressed in meters. (The Science of Color)
Diplopia--The perception of two images of a single object.
Distal--that which lies further from
Dogiel cells--Displaced neurons. Cells which exhibit characteristics usually associated with cells found elsewhere, i.e., action potentials detected in a bipolar cell. May be due to poor investigative technique where excessive capacitance has been added to the cell and it has gone into oscillation.
Dominator element--An early designation used by Granit (1947) to describe putative broadband photoreceptor elements responsible for signals measured within the optic nerve. Archaic with recognition of the signal processing occurring within the retina. See also modulator element.
Donnan potential--The potential across a semipermeable membrane caused by a difference in concentration of ions on the two sides. A more general form of the Nernst potential.
Dorsal--Pertaining to the back. Synonomous with superior.
Dorsal terminal nucleus--A structure of the brain connected to the Pretectum. Part of the Precision Optical System. The interface between the afferent signal paths from the eye and the efferent signal paths to the motor neurons controlling the position of the ocular globes, apparently through the posterior and anterior rectus muscles.
Double layer--1. (Semiconductor physics) The space charge distribution surrounding and defining the location of a junction, either electrolytic or solid state, under equilibrium conditions.
2. (Cytology) A colloquial name for the bilayer membrane forming the external wall of a biological cell. See bilayer.
Duct--In a glandular context, the manifold created in a compound gland between the tubules of individual simple gland cells and the exit point of the compound gland
E-face--Used variously in the literature. See also P-face.
1. Generally: The external face of the plasma membrane of a cell. The face contacting the extracellular matrix.
2. Freeze-Fracture morphology: The hydrophobic surface associated with the external leaflet of the bilayer plasma membrane. This is usually the face of the leaflet facing the other leaflet and toward the plasma of the cell.
Early Receptor Potential--A loosely defined term used by different authors in distinctly different ways when discussing ERG and LERG waveforms:
1. A diphasic waveform occurring within a few microseconds of illumination of the photoreceptor--probably actually due to capacitive coupling between the measuring equipment and the gating circuits of the illumination equipment.
2. A monophasic waveform occurring during the first 50-100 microseconds following illumination and found in LERG's with amplifiers operating at very high sensitivity.
3. The initial transient in the ERG occurring during the first few milliseconds after illumination of the photoreceptor cells.
Efferent--Directed away from a central organ or section. Carrying impulses from the central nervous system to an effector. See also afferent.
Efferescent copy-A putative signal, appearing in the recent literature, returned to the brain from the oculomotor control system or muscles of the eye indicating the position of the eye. This signal is actually extracted from the imagery sensed by the retina and transmitted to the lateral geniculate nucleus of the thalmus.
Efficacy--Power or capacity to produce a desired effect; effectiveness.
Electrolytic cell--A cell containing an electrolyte wherein the conduction of electricity is accompanied by chemical action; in the general case, a reversible process
1. A cell containing an electrolyte through which an externally generated electric current is passed by a system of electrodes in order to produce an electrochemical reaction.
2. A cell containing an electrolyte in which an electrochemical reaction produces an electromotive force
Electro-physics--Knowledge gained from the measurement of electrical responses to physical stimuli
Electrostenolytic Effect--A process involving reactions of oxidation and reduction at the opposite ends of an electronically conducting but high ion resistivity path. Ref: in Marino on page 191.
Electrotonic--A term coined by du Bois Reymond to denote the distribution of potentials in a nerve or muscle polarized by weak currents from externally applied electrodes. Now widely used to refer to non-pulse signals and waveforms resulting from analog circuits within the neural system. (Hille, pg. 27)
ELM--see Exterior Limiting Membrane
Emiocytosis--The expulsion of minute particles by a cell.
Emmetropia--The normal condition of the eye with respect to vision. Myopia is short-sightedness. Hypermetropia is far-sightedness
Endo-combing form meaning "within"
Endogenous--1. Produced or growing from within.
2. Biology. Originating or produced within an organism, a tissue, or a cell: endogenous secretions.
Engram-An abstract vector representing a feature extracted by a feature extraction engine of the (visual) cortex. The engram may be a member of a hierarchal family or a portion of a larger engram. To be differentiated from an analog or pulse signal vector found in the visual system prior to feature extraction.
Enzyme--An organic catalyst; providing a variety of functions and frequently defined in terms of its internal groups and/or the material it catalyzes. The internal groups are frequently a protein element (the apoenzyme) and a non-protein group (the prosthetic portion). Many enzymes require a cofactor or coenzyme to act as acceptors or donors of a functional group that are added or removed from the substrate.
Hydrolytic enzymes-addition or removal of the elements of water
Hydrase-addition or removal of water
Isomerase-catalyze an intramolecular rearrangement
Microsomes--microsomes (particulate bodies) within cells act as (are) enzymes
Transferring enzymes-transferring amide, amino, methyl and other groups
Transporting enzymes (Binding Proteins)
mostly from White, et. al. Principles of Biochemistry, 5th Ed. McGraw-Hill
Epigenesis--The creation of an animal, a phenotype, based on a specific sample of DNA, a genotype.
EPSP-Excitatory postsynaptic potential.
Equivalent Circuit--An electronic circuit used to provide the same performance as another electronic circuit based on the movement of free electrons (and or holes). An equivalent circuit is in apposition to an Analogous circuit which emulates systems that do not utilize free electrons in their operation.
ERG--Electro-retino-graph; A gross measurement, usually employing an electrode attached to a surface external to the eye.
Euryhaline--Having a wide tolerance to salinity variations in the exterior environment.
Exciplex--A higher level exciton complex than defined by a bi-exciton. Found in dicyano- compounds such as dicyanobenzene-napthalene and used in infra-red photography.
Exciton--A mobile but localized non-conducting excited state; an energy packet forming a quasi-particle obeying Bose-Einstein statistics; a boson.
Exocrine Gland-- See Gland
Expanded damped sinusoid-A function describing the precise shape of the dark adaptation characteristic of human vision.
Exterior Limiting Membrane (ELM)--An apparent membrane caused by a close packing of individual structures resulting in an apparent impervious boundary in the general area of the IS; various authors place it at the midline of the IS, directly below the IS on the side nearest the outer nuclear layer, and sometimes near the OS/IS boundary.
Eye--A photodetection device consisting of at least a single photoreceptor cell enclosed in a light tight compartment with an aperture stop. There are four fundamental types of eyes;
1. The occelus, or simple eye, of arthropoda consisting of only one (or at most a few) ommatidia, i. e., a photoreceptor cell behind a lens and enclosed in an opaque housing.
2. The Compound eye of arthropoda consisting of a large group of ommatidia forming a mosaic
3. The Mollusca eye, consisting of a large number of photoreceptors grouped into a retina enclosed into a body mounted enclosure behind a single lens element. The photoreceptor cells are usually mounted in the direct mode, in which the distal end of the cell receives the illumination.
4. The vertebrate eye, more properly chordate eye, consisting of a large number or photoreceptors grouped into a retina enclosed in a enclosure behind a single lens element where the enclosure is rotatable with respect to the animals head. The photoreceptor cells are mounted such that the proximal end of the outer segment receives the illumination.
FAZ--Foveal avascular zone. A region of the retina as viewed from the vitreous humor that describes the area believed to be free from capillaries (See Ahnelt '98). About 250 microns in diameter.
Fechner's Fraction--Ratio of differential luminance threshold to luminance. (The Science of Color)
Fechner's Law-- Just noticeable difference in brightness is equal to a constant fraction of the stimulus (The Science of Color) expressed as L/L=k*B by Bartleson. [See Weber's Law]
Fermi-Dirac distribution law-The quantum mechanical form of the Boltzman-Maxwell distribution law.
Field of View--Not used consistently. Ophthalmologists speak of the field in terms of its half angle or semi-field angle. Most others speak of the total field angle, i.e. Social Security Act, etc.
Flicker--In vision research, usually a light alternating according to a sinusoidal or square wave manner; not wavering erratically
Focal Length (back)--the distance from the back vertex of optical system to the back focal point.
Focal Length (effective)--the distance from the second principal point to the back (or second) focal point. Also, the distance from the front (or first) focal point to the first principal point.
Focal Length (front)--the distance from the front vertex of optical system to the front focal point.
Focal Point--The point to which (paraxial) rays, parallel to the axis, converge , or appear to converge, after passing through the optical system.
1. Front (first) focal point; The focal point to which rays incident from the right are converged.
2. Back (second) focal point; The focal point to which rays incident from the left are converged.
Fornix-The reflection of the conjunctiva from the ocular globe
Fovea centralis--The region of the fovea located at the point of fixation on the retina and exhibiting the highest level of form and color discrimination. Involving about 5000 photoreceptors. No nerve cells overlay this region.
Foveal avascular zone-Used by Ahnelt (1998) to describe an approximately 250 micron (0.57 degree) diameter zone on vitreous side of retina. Fixation point varies within this zone. Historically, the zone is considered "rod free"
G-protein-guanyl phosphate-binding proteins.
GABA--g-aminobutyric acid. A material found in intimate relationship with neurons and frequently with glutamic acid. Presumed to provide electrical energy to the neuron through electromotive action.
Gamut of colors--Total variety of colors that can be produced by any prescribed method (The Science of Color)
Ganzfeld illumination--Illumination of the entire retina so that, as nearly as possible, the entire retina is illuminated at the same level. Normally achieved by observing a uniformly illuminated scene; normally the variation in the f/# of the eye with field angle has not been considered.
Gap Substance--A poly-anionic matrix filling the paranode space external to the nodal recesses.
Gaussian Optics--That branch of optics that illustrates the theory in which u is substituted for sin u in Snell's Law. Effective results are achieved if the aperture and field angle are made very small. Also called paraxial optics or first order optics.
Genotype--A molecule of DNA defining a particular phenotype, animal. See phenotype & epigenesis.
Geranyl ring--See Cyclogeranyl ring
Gland-- A structure capable of creating a specialized substance and excreting the substance onto a surface (exocrine type) or into the blood or lymph streams (endocrine type) Further categorized as to whether the material is passed through the cell wall (merocrine type), breaks through the wall and separating along with part of the wall (apocrine type) or holocrine type where the cell is destroyed in the process of freeing the specialized substance.
Glutamate--A salt of glutamic acid
Glutamine oxidation-A primary energy source in the a-Ketoglutarate pathway of the Krebs Cycle. Found also in a similar pathway supporting the generation of electricity in the neuron.
Type I--Projection neurons, cells with long axons
Type II--Intrinsic neurons, cells with short axons from Noback pg 32 or Dowling, pg 350
Helmholtz Layer--a region of charge concentration in the solution at a solution-semiconductor boundary under equilibrium conditions. Complementary to the Space Charge Layer on the semiconductor side of the boundary.
Helmholtz Theory--See Young-Helmholtz Theory
Herman cable--A transmission line described as a "leaky telegraph line and widely adopted in the physiological literature dating from 1905. It is limited to resistors and capacitors and is not descriptive of a real transmission line of finite bandwidth which requires inductance as a primary constituent.
Hering Opponent Theory-- A response oriented theory based on the hypothesis that humans only "see" six unique colors (black, white, red, yellow, green and blue) and assuming three photoreceptors which yield three kinds of opponent responses: white-black, red-green and yellow-blue.
Histology--The study of biological tissue, with or without the aid of a light microscope
Hole--The absence of an electron from a particular lattice site in a crystalline material. Typically indicated by the symbol, X+ where X can be any atom or complex of atoms capable of giving up an electron. H+ is a typical hole in a hydronium crystal.
Holo--sometimes -olo-, a combining form meaning "whole"; in enzymology used in the sense with combined with or carrying a target material. Opposite of apo-
Homeostasis--The ability or tendency of an organism or a cell to maintain internal equilibrium by adjusting its physiological processes. A vegetative process.
Homeostasis--The maintenance of static conditions in the internal environment
Hormone--A substance secreted into the blood stream which influences tissues and organs so as to differentiate and elaborate new cell types and new enzymes.
Hyperopic--vision at illumination levels over or beyond the normal range
Imaging Sensor--Any sensor system which depends on and expects the line of sight between the scene and the sensor to remain fixed during the period of observation. The photodetection mechanism usually involves an integrating function during the observation interval to achieve maximum sensitivity. A framing sensor is usually an imaging sensor that continually repeats the observation cycle, i.e a television or motion picture camera.
Imp--Intra-membranous particle. Not shown to actually penetrate both bi-layers of a plasma membrane. Believed to be formed by synaptic vesicles deforming the plasma membrane locally.
Incised--in Gray, sharply cut
Inhibition--1. Usually used in the literature in a colloquial sense at the conceptual level to mean a throttling of a signal. Does not recognize the consequences of subtracting two signals.
2. Not used in this work
Inion--a nodal point at the rear of the head used in VEP (visual evoked potential) research as a point of physical and electrical reference.
Initial segment--An unmyelinated area associated with the axon hillock that is the location of the Activa in a neuron. It is recognized as being a specialized region of the plasma membrane. It is the degenerate form of the podite terminal of the neuron.
Inner Segment--The portion of the photoreceptor cell of Chordata associated with the secretory functions involved in forming the protein substrate of the disks found in the Outer Segment.
Interneuron--A neuronwhich is not used to transmit signals over long distances in the animalbut to perform a variety of signal processing functions. See also Projection neuron.
Invertebrates--A loose term used to describe non-chordates
Iodopsin--A putative chromophore of vision having a peak spectral absorption at 560 nm. This spectral peak is obtained in "difference spectra" assuming the signals generated by the chromophores of vision are manipulated in linear algebraic space in the animal eye. Can also be observed psycho-physiologically as one of the Brezold-Brucke peaks in the human Luminous Efficiency Function..
IPM--Inter-Photoreceptor Matrix, the fluid found in the cavity between the RPE and the layer of photoreceptor Inner Segments.
IRBP--Inter-retinal Binding Protein
Ipsilateral--Located on or affecting the same side of the body
Isomers--Different compounds that have the same molecular formula. It is the structure, both geometric and electrical, that differentiates the properties of the compounds.
Isoprene Rule--A guide to the understanding of how many biological molecules are constructed from simpler non-biological molecules, often before they are further modified to satisfy specific applications.
J-band--The spectral absorption band exhibited by a chromophore of the resonance hybrid type when existing in the liquid crystalline state.
K- upper case A constant frequently used in photon-quantum mechanical interactions. Equal to the Boltzman constant divided by the product of Planck's Constant and the speed of light. Frequently given as 1/48 at room temperature. Equal to 1/46.34 at nominal human body temperature.
Kite, White Tailed--Elanus leucurus of the Order Falconiformes. They hover in flight between 10-20 meters above the ground with their head held still in inertial space relative to the earth while watching for the movement of prey on the ground below. When attacking, they do not dive, but slip downward feet first while maintaining their line of sight.
Krebs solution--An electrolyte used to maintain an external environment compatible with an excised cell. Typically a mixture of NaCl, MgSO4, CaCl2 and NaHCO3. It contains no nutritional or metabolic component more complicated than dextrose or oxygen.
Krebs Cycle-Also known as the Krebs tricarboxylic acid cycle. The prototypical metabolic energy cycle in animals. It involves the consumption of fatty acids through their multi-step reduction to either urea or ammonia. One path of entry into the Krebs Cycle is via the a-Ketoglutarate pathway. This pathway employs the glutamines.
Labile--in chemistry; unstable, metastable
Lamina Cribosa--A structural membrane at the rear of the eye penetrated by the individual neurons of the optical nerve bundle on their way to the brain. Literally, a sieve like sheet.(Howell in ARVO notes to pg I.18)
Late Receptor Potential--Labeled by Snyder & Menzel but not defined explicitly
Latency--No unique definition. Used by different investigators to define the time interval between;
Lateral geniculate bodies--portions of the thalamus that receive neural signals from the optic nerve and distribute them to the cortex, mainly areas 17 & 18
Lateral terminal nucleus--A structure of the brain. One of three small nuclei in the Precision Optical System. The interface between the afferent signal paths from the eye and the efferent signal paths to some of the motor neurons controlling the ocular globes.
Lecithin--Choline phosphoglyceride, also known as phosphatidyl choline
Lenticular array--In optics, a two dimensional array of small lenses, each individual lens having a shape reminiscent of a lentil.
Ligand--An ion, a molecule, or a molecular group that binds to another chemical entity to form a larger complex. See prosthetic group in the case of a conjugated protein.
Light--Electromagnetic radiation with a wavelength such that it is transmitted through the optical window in the absorption spectrum of the atmosphere; generally from 0.3 microns to a few tens of microns. Different animals perceive different portions of this spectrum as "visible light" for that species.
Limbic system-Archaic name for a group of elements in the brain originally thought to be concerned with the olfactory process. Nominally the rhinencephalon of the midbrain. See page 34 of Hamilton.
Lipid--A water insoluble organic substance found in cells which are extractable by non-polar solvents such as ether, benzene, chloroform. [With a long (usually even numbered and never conjugated) hydrocarbon chain with a carboxyl group on the end; Lehninger, pg 189-190]
Lipoid--A fat or fat like substance; Gray
Liquid crystal--A material in a mesophase of matter existing between the liquid and crystalline states of matter. Frequently a temperature sensitive state. If deposited on a substrate, it will exhibit many optical features of a crystal. Mesophases include both the smectic and nematic types The smectic is the more ordered of the two. [Adamson, A. Physical Chemistry pg 1006] The chromophores of vision are thought to be of the smectic type.
Local Electro-retinogram- LERG--An analog extracellular response obtained from a localized region of the retina by an electrical probe and representing the sum of the signals (varying in waveform and time) from many cells.
Logistic Curve--A name taken from the statistics of population growth and also known as a hyperbolic tangent given by the expression y = 1 + tanh x
Luneberg Len--A lens usually used at microwave frequencies to shape an incident radiation wavefront through the variation in the local index of refraction within the lens instead of using the shape of the external surfaces of the lens. At optical wavelengths, a glass exhibiting a variation in index of refraction with distance from the optical axis, thereby providing an additional degree of design freedom to the design engineer
Lyotropic--Lyotropic systems are formed by the dissolving of one material in a second material.
Macular sparing-A condition encountered in situations where V1 is essentially destroyed but the subject can still read and fixate on objects.
Matthiessen's ratio-The focal length of a lens divided by the radius of that lens. This definition does not incorporate the pupil size of the lens system. In this way, it differs from the f/# of an optical system
M-channel--The pathway leading from the retina to the magnocellular region of the brain
Macula lutea--Spot near the posterior pole of the eye within which the retina is somewhat thickened and has a yellowish color. (The Science of Color)
Maintained response--A steady state response generally to a step input stimulus
Maxwellian View--A method of using a lens to create an image of a source in the aperture stop of the eye while the eye is focused on the lens.
Medial terminal nucleus--A structure of the brain. One of three distinct small parts of the Precision Optical System. The interface between the afferent signal paths from the eye and the efferent signal paths to the motor neurons controlling the ocular globes, apparently the superior rectus and inferior rectus.
Meridional plane--Any plane tangent to (containing) the optical axis
Merocrine Gland--See Gland
Mesopic--vision utilizing the middle range of illumination
Metabolism--The molecular level events involved in the synthesis, assembly, maintenance, and turnover of cells, groups of cells and components of cells in an animal. The function includes the provision of power to the neural system but not the processing and transmission of signals.
Methine Radical-- --CH=
Methyl Radical-- CH3-
Methylene Radical-- -CH2- A free radical of the diradical type (Morrison & Boyd, pg. 134). Able to insert itself into alkane molecules.
Meyer's Loop-The fan-like portion of the optical radiation following the LGN. It provides a timing delay to compensate for the different ganglion axon lengths with position in the retina.
1. Biochemistry--A globule of lipid molecules in water where their nonpolar ends face inward and their polar tails face outward.
2. Chemistry--A colloid particle formed by an aggregate of small molecules.
Michaelis Equation--An equation of the form y = x/c + x where c equals x at the point where y equals ½ of its maximum value. Also known as the Michaelis-Menton equation, the logistic equation and a variety of other names.
Micro--prefix a. Small: microcircuit.
b. Abnormally small: microcephaly.
c. Requiring or involving microscopy: microsurgery.
Modulator element--An early designation used by Granit (1947) to describe three putative narrowband photoreceptor elements responsible for signals measured within the optic nerve. See also modulator element.
Monkeys-Among the most advanced mammals but the least advanced mammals of the Order Primates. Animals widely used in the research phase of vision. Found in two major Superfamilies, Ceboida (New World monkeys) and Cercopithecoidea (Old World monkeys). Functionally interchangeable with humans from the perspective of research on the signaling aspects of the visual system distal to the optical chiasm at the entry to the brain. Not completely interchangeable with regard to the foveola and the Precision Optical System controlling ocular motion. Not interchangeable with respect to research on the cortex and midbrain of the human. The degree of difference between the monkey (particularly the New World monkeys) and human brain is significant morphologically, topographically, functionally and organizationally. See Primates.
Morphology--The branch of biology that deals with the form and structure of organisms without consideration of function.
Muller's Law-- Nerve impulses of all senses are of same kind (as defined in The Science of Color glossary); generally elucidated prior to the recognition of the electrotonic nature of some retinal neurons
Nanobiology--A popular name for the branch of biology concerned with subcellular structure and function.
Nasal--The side of the retina nearest to the nose
Nauplius eye--Variously used to describe a simple, more likely ocellus type, eye in Arthropoda. Sometimes referring to an eye formed during one of the larval stages of an animals development.
Nernst potential--The potential across a semipermeable membrane caused by a difference in concentration of one ionic species on the two sides. A more limited form of the Donnan potential of physical chemistry.
Nerve root--The point where a nerve enters or leaves the spinal chord of Chordata. A dorsal nerve root is associated with an afferent (sensory path) neuron. A ventral nerve root is associated with a efferent (motor path) neuron.
Neural Propagation Velocity--Typically 50 meters/sec in large unmylinated neural fibers to 120 meters/sec in small myelinated neural fibers.
Nictating lens--An adaptation of the auxiliary eyelid in amphibian members of Chordata to provide proper image focus when changing from an atmospheric to aquatic environment. Variant of nictitating derived from medieval Latin for winking.
Nodal Planes --(For paraxial analysis of optical systems) Planes perpendicular to the optical axis at the point where the nodal points are located on that axis.
Nodal Points--(For paraxial analysis of optical systems) Two axial points of an optical system, so located that an oblique ray directed toward the first appears to emerge from the second, parallel to its original direction. For systems in air, the nodal points coincide with the principal points. For highly oblique, i. e., non-paraxial, rays, nodal points may not exist.
Node of Ranvier-- A feature of the axon of longer length neurons. Constitutes a point of amplification and is the site of an Activa and its associated circuit elements.
Non-spherical lens--a lens of a fundamental shape other than a sphere. Usually a lens based on a conic section or a cylinder. It may be intentionally deformed slightly to improve its aberration performance. In this case, it is described as an aspherized cylindrical (or elliptical) lens.
Null--An undefined condition, not a zero, not black
Numerical Aperture--An expression of the light collecting capability of an optical system given by:
n. a. = nd/2p where n=index of refraction of the medium, d=diameter of the aperture, and p=focal length of the lens.
Nystagmus--This term is used variously to describe both normal and pathological conditions.
1. A pathological condition involving an uncontrolled oscillatory movement of the axes of the eyes during which the amplitude of oscillation is tens of hundreds of times greater than the amplitude of the tremor, while the frequency of the nystagmus is tens of times lower than the frequency of the tremor. (Yarbus pg 120)
2. Pursuit nystagmus, generally not exhibited until several month post- partum in humans and probably learned, is the ability to maintain the image of a smoothly moving object on the point of fixation of the retina.
3. Optikokinetic nystagmus allows the eye to track successive points in a continuously moving scene. It is characterized by a slow component in the direction of scene movement during observation and a fast component in the opposite direction as the line of fixation jumps to a different location in the scene. This appears to be a learned capability in man.
Ocellus--1. A small simple eye, found in many invertebrates, usually consisting of a few sensory cells and a single lens.
2. One of the elements of a compound eye
Converse ocellus, one in which the distal end of the retinal cells receive the light
Inverse ocellus, one in which the proximal end of the retinal cells face the light
*** This definition does not agree with Shepherd pg. 331 ***
Occipital--pertaining to the posterior third of the chordate head
OFF-center--Traditional classification in psychophysics; actually indicative of a "negative contrast" or a lowering of stimulus level below a nominal level and not a truly "off" or black condition. (see Kulikowski, Seeing Contour & Color)
Ommatidia--The individual sensor element of the compound eye, consisting of a rhabdom located behind a light collecting structure, which may or may not contain a lens. See ocellus
Ontogeny--The total of the stages of an organisms life history
Oocyte --A cell from which an egg or ovum develops by meiosis; a female gametocyte
OPD (optical path difference)--The fundamental descriptor of the quality of an optical system. A complex function describing every ray that passes through an optical system from an object point. It consists of first order (Gaussian) terms, third order (Seidel) terms, fifth order (Buchdahl) terms, and higher order terms. See the Infra-red Handbook, Washington, DC: Office of Naval Research 1978, pg 8-17
Ophthalmics--The correction of excessive departures from normality by the introduction of supplementary eye-lenses.
Ophthalmology-- The branch of medicine that deals with the anatomy, functions, pathology, and treatment of the eye.
Optic disk--The area on the surface of the retina where the optic nerves leave the eye. Also known as the papilla or the "blind spot."
Optical Analysis--Frequently carried out in four degrees of completeness. [check these terms ]
1. First Order Analysis, frequently spoken of as Gaussian Optics and limited to the paraxial condition.
2. Third Order Analysis, concerned with spherical aberration and defining the Petzval surface of the optical system.
3. Fifth Order Analysis, concerned with coma, astigmatism and chromatic aberration.
4. Complete Analysis, which entails a complete ray trace of the optical system, both paraxial and off axis rays, and a full description of the image surface, image distortions, magnifications, etc.
1. Dioptrics; optical elements based on refraction, lenses
2. Catoptics; optical elements based on reflection, mirrors and waveguides
3. Catadioptrics; optical systems employing both refraction and reflection
Optokinetic reflex-Archaic, see Optokinetic response
Optokinetic response-(OKR)--The rotational response of the eyes due to signals derived from the retina as well as other auditory and somatosensory inputs.
Ordinate-Distance from the horizontal axis in a two-dimensional plot.
Orthodromic--In the normal direction of signal flow in the nervous system
Osmosis-- Diffusion of fluid through a semipermeable membrane until there is an equal concentration of fluid on both sides of the membrane
P-channel--the pathway leading from the retina to the parvocellular region of the brain
P-face---Used variously in the literature. See also E-face.
1. Generally: The internal face of the plasma membrane of a cell. The face contacting the plasma of the cell.
2. Freeze-Fracture morphology: The hydrophobic surface of the internal leaflet of the bilayer plasma membrane. This is usually the face of the leaflet facing the other leaflet and toward the external medium surrounding the cell.
Pallial eyes--Eyes located on the mantle. As opposed to cephalic eyes located on the head.
Papilla--see optic disk
Paraxial Ray--A ray which makes a very small angle with the optical axis and lies close to the axis throughout the distance from object to image.
Parietal eye--An eye located on the parietal bone of the head
Pectal--(Latin for Breast area)
Perfuse--To pass a liquid through the interior of a cell or part of a cell. See also superfuse
Peripheral nervous system-The system primarily concerned with the control of the skeletal muscles.
PERG--Pattern electroretinograph, a frequency response function obtained by varying the contrast of a checkerboard or sine wave pattern while changing the pattern pitch in steps. Results are strongly dependent on the specific spectral wavelengths employed to achieve the contrast.
Perikaryon--A general description of the cell body of a neuron, containing the nucleus and organelles. In most cases also containing the active element, the Activa.
Phagocytosis--The process of engulfing solid particles in the process of digesting or further processing them.
Phasic--Poorly defined but generally an adjective relating to a transient process; as opposed to tonic. In some spectral work, used to describe the shape of the response waveform (particularly the number of times the waveform reverses polarity, hence monophasic, biphasic and triphasic)
Phenotype--An animal resulting from epigenesis based on a specific genotype of DNA.
Phosphene-1. The dark circular spot in the visual field caused by mechanical pressure on the ocular globe on the side directly [only an approximation] opposite the spot. (See Adler's)
2. Perceived flash (unstructured image vector) from a surgically implanted electrode stimulating the visual cortex. They appear as white spots on "black."
Phosphoglycerides--Polar lipids found almost exclusively in cell membranes.
Photopic Vision--Vision at moderate and high levels of luminance (in humans)
Photochromatic interval-The difference in threshold sensitivity of the chrominance and luminance channels in human vision. The interval is a function of spectral content in the test irradiance and possibly additional secondary processes within the visual system. The interval contains a large transient component.
Physiology--The biological study of the functions of living organisms and their parts
Sub-disciplines according to Dowben:
1. Physiological chemistry (or more recently Biochemistry).
2. Systems physiology--study of functional integration.
3. General physiology--concentration at a cellular level based on molecular structure
and in terms of chemical and physical principles.
Pitt's Law--The differential wavelength discrimination in the color-defective patient is best where the intrinsic saturation is poorest.
Planck's Law of Radiation--The law and equation defining the spectral radiation from a perfect blackbody. Usually plotted with respect to wavelength, temperature being a parameter.
1. (Electrolytic semiconductor chemistry-) The descriptors used to define the types of semiconductor material forming the Activa, the active three terminal electrolytic semiconductor device analogous to the transistor. Adapted from its use in solid state semiconductor physics.
2. (Morphology) The paranode-node-paranode region describing a Node of Ranvier. Can also be defined as the pre-node/node/post node region defining the active region of the Node of Ranvier.
Poda or Poditic terminal-The neurite terminal of the Activa providing signal inversion between the Poda and the Axon. Also known as the basilar dendrite (but more properly the basilar neurite) in some literature.
Polyene Dyes--Organic chemicals characterized by a conjugated chain of methine groups terminated by alkyl or other groups which do not influence the electronic excitation of of the dye. The molecule is normally in E (trans) configuration. (Zollinger 1991)
Polymethine Dyes--Organic chemicals characterized by a conjugated chain of methine groups terminated by an electron donor D on one end and an electron acceptor A on the other. The molecule is normally in E (trans) configuration. (Zollinger 1991)
Posterior--The hinder part of an organism
Porphyropsin-- Synonymous with Rhodonine(7) in its liquid crystalline form and exhibiting a peak anisotropic spectral absorption at 532 nm.Archaic: A name in the literature for the visual pigment based on a protein, opsin, and a chromophore based on vitamin A2 and hence retinene2
Postsynaptic--Generally referring to elements proximal to a sensory synapse.
Precision Optical System--Also known historically as the Auxiliary Optical System. A set of functional parts of the brain acting as the interface between the afferent signals from the eye and the efferent signals passing over the motor neurons to the muscles controlling the position of the ocular globes.
Presynaptic--Generally referring to elements distal to a sensory synapse, typically a presynaptic neuron is providing the signal to the postsynaptic neuron
Primates-The highest Order in the Class Mammalia in the Phylum Chordata. Consists of the Superfamilies Homoinoidea (man and the higher, anthropoid, apes), Ceboida (New World monkeys) and Cercopithecoidea (Old World monkeys). All of these animals have visual systems distal to the optic chiasm that are similar. There are significant differences proximal to the optic chiasm. While the rhesus monkey (Cercopithecoidea macacus) is widely used in visual research, only the Pongidae family of Homoinoidea are sufficiently similar to man to be interchangeable at the functional and topographic level of the cortex and mid brain. Pongidae includes the gibbon, orangutan, chimpanzee, and the gorilla.
Principal Planes (Surfaces)--(The Principal Planes are planes only in the paraxial region; at any finite distance from the axis they are figures of rotation, frequently approximating spherical surfaces.)
If each ray of a bundle, incident on an optical system parallel to the axis, is extended to meet the backward extension of the same ray after it has passed through the system, the locus of the intersections of all the rays is called a principal plane. The first principal plane is formed by rays incident from the right. The second principal plane is formed by rays incident from the left.
Principal ray--The ray that passes through the middle of the aperture stop from an extra-axial object point is called the principal ray of an oblique beam.
Process--1. A series of actions, changes, or functions bringing about a result: the process of digestion; the process of obtaining a driver's license.
2. A series of operations performed in the making or treatment of a product: a manufacturing process; leather dyed during the tanning process.
3. Biology. An outgrowth of tissue; a projecting part: a bony process
Projection neuron--A neuron used to transmit nervous signals over long distances in the animal.
See also Interneuron.
propioceptors--Sensory cells related to the physical state of the organism, particularly the pressure sensitive neuro-receptor cells
Prosthetic group--The non-amino acid portion of a conjugated protein. See ligand in the case of non-protein conjugated molecule.
Protanomaly--Form of anomalous trichromatism for which, in a red-green mixture, more than the normal amount of red is required to match a particular yellow (The Science of Color)
Protanopia--Form of dichromatism in which red and bluish-green are confused, and relative luminosity of red is much lower than for normal observer (The Science of Color)
Protostomia--That large class of bilaterally symmetrical animals generally characterized by a notochord located along the ventral surface of the animal
Proximal--that which lies nearer to
P.s.p--Used variously by authors to indicate the pre-synaptic potential or post-synaptic potential
Psychophysics--Knowledge concerning the relations of subjective responses to the acting physical stimuli
Puncta adhaerentia--Tiny holes, spots or points sticking to a surface. Used by Raviola & Raviola.
Pupil, Entrance--The image of the aperture stop formed by the optical elements ( if any) between the aperture stop and the object. The image of the aperture stop as "seen" from the object. The entrance pupil appears to lie 0.5 mm. in front of the actual aperture stop formed by the iris.
Purkinje cell--The only recognized type of output neuron of the cerebellar cortex. It produces action potentials.
Purkinje Shift--Defined by this author (1985) as the unique characteristic of the perceived spectral sensitivity wherein the peak sensitivity moves, as the light level is reduced, from a peak near 580 nm.to a peak near 530 nm.without ever exhibiting a peak in the region of 550 nm. The minimum in the graph of the minimum discernable wavelength versus wavelength also shifts in this manner. Other authors have indicated different values for the peak wavelengths involved.
Purple Line--The construction line in the C.I.E. (1931) Chromaticity Diagram drawn arbitrarily between points considered to be at the extremes of the visible spectral locus. Usually shown as drawn between the x,y coordinates associated with 380 nm. point and the x,y coordinates associated with the 700 nm. point on that diagram.
Putative--Generally regarded as such; supposed or proposed.
Ranvier, Node of-- See Node of Ranvier
Ray, Chief--A ray directed toward the center of the entrance pupil of the optical system.
Ray, Principal--Strictly, a ray directed toward the first principal point, but commonly used to refer to the Chief Ray.
Rayleigh equation--Actually a shorthand notation according to Rubin and Walls; used as a basis for the Nagel Anomaloscope; "a" amount of red plus "b" amount of green equals "c" amount of yellow.
Resonance--Used in three distinct manners.
1. A condition where a single molecule can assume more than one electronic state while maintaining the same structural arrangement.
2. The property of a single molecule that causes it to vibrate mechanically at a specific frequency related to the wavelength of light.
3. A property of a liquid crystalline structure, related to its slow wave structure, that causes it to be electrically excitable by photons of a particular wavelength striking the crystal perpendicularly to its surface.
Resonant Dyes--Dyes consisting of two polar atoms separated by a conjugated chain, usually of carbon atoms, frequently of the vinylene type. These dyes exhibit two distinctly different structures depending on the state of the electronic charge associated with the dye. These dyes differ only in the way the electrons are disposed, not in the location or configuration of the atoms. See the Resonance Theory of Dyes.
Retinal--The simple aldehyde of Vitamin A. Peak isotropic spectral absorption at ~330 nm.
Retinene--The simple aldehyde of Vitamin A (also known as retinal )
Retinula--The photoreceptor cell(s) at the base of an ommatidium, forming the rhabdom.
Retinochrome-- non-signal related but possibly photosensitive pigments frequently found in the interstitial spaces between rhabdom(ere)
Retonic Acid--Vitamin A acid.
Retinoids--Definition has and is still evolving. First used in the 1960's informally for the natural forms of retinol. Formally defined in 1976 by Sporn et. al. to broaden the term beyond the vision and nutrition aspects to include potential biologic and mechanistic relationships between metabolites of retinol and steroids. The IUPAC-IUB (1982) Joint Commission on Biochemical Nomenclature stated that: "Retinoids are a class of compounds consisting of four isoprenoid units joined in a head -to-tail manner." In 1994, Sporn & Roberts (1985) suggested the much broader definition of a Retinoid as any substance that: "can elicit specific biologic responses by binding to and activating a specific receptor or set of receptors, with the program for the biologic response of the target cell residing in the retinoid receptor rather than in the retinoid ligand itself.
Retinol--Vitamin A. Peak isotropic spectral absorption at ~370 nm. No significant absorption in the visible spectrum
RBP--Retinoid-Binding Protein, a generic descriptor. Archaic: Retinol-Binding Protein. The material exists in a variety of forms at different locations within the body. Some of the forms are still speculative.
LRBP-putative form found in the lacteals of the lymph system and in the liver.
CRALBP- form found in the RPE and believed to transport chromophores from pigment granules to the cell wall at the IPM interface.
CRBP-form found in the RPE and believed to transport chromophores from the blood interface to storage within pigment granules.
IRBP-form found in the IPM and used to transport chromophores from the RPE interface to the surface of the disks
PRBP- form found in blood plasma and used to transport retinol from the liver to the RPE interface, in conjunction with TTR
SRBP-Alternate, and more specific label for PRBP. The RBP is probably one of the globulin proteins which makes up 38% of the total protein in plasma.
RSC--reverse saturation current. A fundamental electrical parameter of a diode indicative of its current carrying capacity as a function of voltage.
RGC-Retinal ganglion cells
Rhabdom--The sensory assembly in the compound eye, consisting of a cylindrical structure illuminated from the end, frequently exhibiting a ciliary internal structure consisting of the rhabdomere of 9 (individual) photoreceptor cells (Stavenga, pg 30 & 283). Also used to describe a similar assembly in the complex eye of Mollusca. There are two types, the open and closed rhabdomere. Looking along the line of incident radiation, the open rhabdomere (primarily in Mollusca) exhibits a series of small areas of chromophoric material that are arranged in a circle and isolated from each other. The closed rhabdomere (primarily in Arthropoda) has larger areas of chromophoric material that are interleaved.
Rhabdomere--A dense microvillous structure carrying the photosensitive pigments associated with a photoreceptor cell in Arthropoda and Mollusca.
Rhodonine()--A family of visual band chromophores prepared from Vitamin A aldehyde (retinene) through the addition of a second auxochrome using a single bond at carbon position 5, 7, 9 or 11. The numeric in the parenthesis indicates the number of vinylene residues between the auxochromes; 2 for the UV chromophore, 3 for the Blue, 4 for the Yellow and 5 for the Red chromophore.
Rhodopsin--A conceptual compound proposed as the principle chromophore of vision with a peak isotropic spectral absorption at 500 nm. First proposed by Boll in 1876 as the photosensitive element of the rod pigment. Further elucidated by Kuhne during the following year. Investigated intensely by Wald and associates in the 1930-50's. They postulated a large molecule consisting of the 11-cis form of retinene combined with the protein Opsin. It has been proposed that the junction involves the epsilon nitrogen of the lysine group (lys-296) of Opsin in a protonated Schiff-base linkage. Never demonstrated. The peak absorption at 500 nm. is actually an anisotropic peak computed by the brain from other spectral inputs.
Ricco's Law-- For small areas of the retina, a constant (psychophysical) effect is achieved for a constant product of area and illumination.
Ringer solution--A man made aqueous solution of the chlorides of sodium, potassium, and calcium that is isotonic to animal tissue (but species specific for accurate scientific work) and is used topically as a physiological saline and, in experiments, to bathe animal tissues. Unless specifically modified by an investigator, it contains no nutritional or metabolic components.
Rods--1. A morphological descriptor terminating a continuum used in vision research. The continuum extends from a cone shaped structure on one end to a rod shaped structure on the other. This continuum was first used to describe the outer segment of the photoreceptor cell. However, this proved unworkable and it was later applied to the shape of the inner segment without regard to the shape of the outer segment. This approach was also unworkable.
2. A term previously used to describe the broad spectral photoreceptor of the eye responsible for the scotopic spectral characteristic of vision. Subsequently it was found that there are "blue" sensitive, "green" sensitive and "red" sensitive rods; and none of them exhibit a spectral absorption that correlates with the scotopic spectral characteristic of the human eye.
3. The term is archaic . It is not used in this work in a scientific sense.
S-Plane--An early name for the region of the retina (more recently described as the inner nuclear layer ) where bipolar waveforms were first found that exhibited a hyperpolarization at certain wavelengths and a depolarization at others. Now further differentiated into the Outer lateral, Outer Plexiform, Inner nuclear, Inner plexiform, and Inner lateral layers.
S-potential--A sustained response found in the layers between the photoreceptor and ganglion layers, name generally associated with Svaetichin and with Tomita but may be from Motokawa. The S-potentials frequently exhibit chromatic characteristics.
Saccades--A sharp rotation of the optic axes characterized by an almost identical movement in both eyes and a high velocity. The angle of rotation ranges between 2-5 minutes of arc to 20 degrees. The maximum velocity reached in a 20 degree saccade can be 450 degrees/sec. The time of a saccades ranges from 0.01 sec to 0.07 sec. (Yarbus, pg 146)
Sagittal--like or related to an arrow
1. Zoology A longitudinal plane that divides the body of a bilaterally symmetrical animal into right and left sections
2. Optics A plane perpendicular to the meridional (a tangential) plane and containing the chief ray.
Saliency engine-A higher level mechanism in perception that provides the addresses of pieces of perceived information that must be considered as a group to achieve cognition. The various vectors, relating to the perceived information, when grouped act as individual bytes in the overall cognition vector describing the recognized event.
Saliency spreadsheet-A putative collection of high level cognition vectors (or series of addresses to lower level perception vectors) that constitute the basis of cognition.
Saltatory--Proceeding by leaps rather than by smooth transitions
Saponification--The hydrolysis of glycerides. The hydrolysis yields salts of the carboxylic acids. Almost certainly a destructive process when related to isolation of vision chromophores
Scanning Sensor--Any sensor system which senses differences in the signal presented to the sensing element as a continuous function of time. If physical motion of the line of sight is involved, the sensed signal may represent spatial changes in the scene.
Schematic--A structural or procedural diagram, especially of an electrical or mechanical system.
Schematic Eye--A simplified model of the optical system of the eye; consisting of only two principle points and two principle planes. Only useful for the on-axis, small field angle case.
Schiff-base--A reversible reaction between an aldehyde and the alpha-amino group of an amino acid releasing water and resulting in the replacement of the double bonded oxygen with a double bonded nitrogen of the amino acid. A very labile product. The protonated Schiff-base is characterized by its ability to shift from an acid to a base depending on the ph of its environment. (Stavenga, pg 115) (-C=N-), prefix azo-
Scotopic Vision--Vision at very low levels of luminance (in humans)
Self screening-- Or correction for self-screening. An archaic concept found in the vision literature based on an approximation associated with the absorption of light by low molar concentration materials in true solutions. Its purpose was to avoid using a very simple equation derived with the Calculus. Generally not appropriate for research in the actual visual process. See Section 220.127.116.11.1 or Wyszecki & Stiles, 2nd. pg 588-589.
Serif--A small decoration(s) added to the characters of a type face to enhance its legibility and general attractiveness. San serif is the trade terminology for "no serif."
Sigmoidal-Anatomy, curved in two directions; shaped like the letter S or the letter C. Generally an S shaped curve in the vision literature. In the absence of added noise, a smooth transition (no discontinuity) between a sigmoidal curve and a baseline is not compatible with a first order physical system.
Single Lens Compound Eye--A transitional type, found in some insects, between a superposition type of compound eye and the simple eye of animals.
Sink-In electronics, an absorber of electrical energy. In electronic circuits, a negative terminal of a power supply.
Soma--The portion of a nerve cell that contains the nucleus but does not incorporate the dendrites or axon.
Source-In electronics, a supplier of electrical energy. In electronic circuits, a positive terminal of a power supply.
Spectra--See Absorption spectra, Difference spectra, Spectral absorption curves and Spectral response curves
Spectral absorption curves--A graphical presentation based on spectrophotometric measurements on material extracted from a retina after a standardized but poorly understood separation process. The tests are designed to provide in-vitro measurements of chromophore like material that is no longer in the liquid crystalline state and which has been subjected to detergents, surfactants, and various complex sodium based salts. The resultant absorption curves are usually due to a (unknown) mixture of materials (chromophores, retinachromes and other materials), frequently exhibiting a peak near 500 nm. which is most likely the intrinsic (as opposed to the resonant) spectral peak of the dominant constituent.
Spectral Opponency- In neurophysiology, the neural mechanism that codes for hue contrast in the insect brain. In this work, synonomous with function of the horizontal cells of the human retina and similar differencing cells throughout Arthropoda and Mollusca, not just in insects.
Spectral response curves--1. The basic graphical presentation of the electrophysical response of any single type of complete photoreceptormechanism to a varying monochromatic stimulation.
2. . The basic graphical presentation of the electrophysical response of any neuron cell in the retina, typically one of the amacrine type, to a varying monochromatic stimulation
3. The basic graphical presentation of the psychophysical response of any overall retina, generally as a function of location on the retina, to a varying monochromatic stimulation.
Stefan- Boltzmann statistics--
Strabismus--A pathological failure of the two eyes to converge on a given target in the visual field. Found in horizontal, vertical and torsional situations.
Stereopsis-The process of merging the two images, acquired by the eyes from different points in space, into a useful image by eliminating the parallax and obtaining distance cues. See Hubel (1988)
Sucrose gap chamber--A three chamber test cell used by Bowe, Kocsis & Waxman to isolate and superfuse distinct parts of a neuron during in-vitro electrophysiological testing.
Super colliculus-See Tectum
Superfuse--To surround a cell with a liquid, frequently disturbing the coatings on the surface of the cell. See also perfuse
Superposition Eye--A compound eye wherein the ommatidia are not optically isolated. Anatomically, these eyes are characterized by the presence of an un-pigmented space separating the optical array from a much deeper-lying retina of rhabdoms. (Stavenga, pg 50)
Synapse--From the Greek, meaning to come face to face with or to join. A specialized site of functional interaction between neurons. The area in the immediate vicinity of the synapse is critical to the operation of this feature.
Syncytium--A multinucleate mass of protoplasm resulting from a fusion of cells or from a failed subdivision of cells.
Tapetum--A layer of cells located behind the retina, relative to the direction of the incident light, in many animals. In many cases, this layer exhibits a high coefficient of reflectance. In some cases, the reflectance is variable with illumination level or other parameters. Also known as argentea.
Tectum-Also known as the super colliculus in mammals. A portion of the midbrain focused on the initial generation of motor responses.
Teleology--1. Philosophy. The study of design or purpose in natural phenomena.
2. The use of ultimate purpose or design as a means of explaining natural phenomena
Teleostat-- "Bony Fish" of the Superorder Teleostei, Class Osteichthyes, Phylum Chordate
Temporal--The side of the retina farthest from the nose
Tetartanopia--Rare form of dichromatism in which blue and yellow are confused, but luminosity is approximately normal (The Science of Color)
Tetrachromats--Animals which employ photoreceptors containing four different color chromophores, known to include some insects, reptiles and fish; and able to sense the "red", "green", "blue" and "ultraviolet".
Thalamus-1. Archaic Anatomy. A large ovoid mass of gray matter situated in the posterior part of the forebrain that relays sensory impulses to the cerebral cortex.
2. The inner chamber. Part of a very complex area between the top of the spinal cord and the proliferation of the cerebral cortex. Easily looked upon as a mere switching point but clearly performing significant signal manipulation within its numerous individual engines. It incorporates the lateral geniculate bodies but not the pretectum.
Tonic--a. As used in Physiology. Of, relating to, or producing tone or tonicity in muscles or tissue: a tonic reflex. b. Medicine. Characterized by continuous tension or contraction of muscles
Topology--1. Topographic study of a given place, especially the history of a region as indicated by its topography.
2. Medicine. The anatomical structure of a specific area or part of the body.
3. Electronics. The description of an electrical circuit in terms of its elements and their geometric relationship to each other.
Transducin--A G-protein proposed in the literature to be activated by rhodopsin in conjunction with rhodopsin kinase.[Crouch 1996] It is a material found in the glutamate cascade theory of photodetection
Transduction--Creation of an excited electron within a chromophoric layer of the OS of the photoreceptor cell as a result of the absorption of a photon
Translation--Creation of a free electron within the signal channel of a dendrite connected to the neuron located within the IS of the photoreceptor cell as a result of the de-excitation of an excited electron in an adjacent chromophoric layer of the OS
Translucent--Transmitting light but causing sufficient diffusion to prevent perception of distinct images
Tremor--The fine angular vibration of the eye used to provide relative motion between the scene and the eye, thereby allowing the change detectors of the eye to create signals used by the brain to perceive an image. The amplitude of the tremor is the most important parameter. It is reported to be 20-40 arc seconds in Man (corresponding to one or two photoreceptor diameters in the fovea). The frequency in Man is difficult to measure, the data ranges from 30-90 Hertz with reports to 150 Hertz.
Trichromats--Animals which employ photoreceptors containing three different color chromophores; known to include two separate classes, those able to see in the "red", "green" and "blue" and those able to see in the "green", "blue" and "ultraviolet".
Tritanopia--Form of dichromatism in which blue and yellow are confused and relative luminosity of blue is much lower than for normal vision (The Science of Color)
Tubule--In the glandular context, the pocket like structure formed by the glandular cell wall and opening on the external surface of the cell or a group of cells.
Ultra- prefix 1. Beyond; on the other side of: ultraviolet.
2. Beyond the range, scope, or limit of: ultrasonic.
not specific as to which side of a range; see micro--
Univariance Principle--Each visual pigment can only signal the rate at which it is effectively catching quanta; it cannot also signal the wavelength associated with the quanta caught (Naka & Rushton, 1966 pg 538)
Uvea--The vascular tunic of the eye
Ventral-synonomous with inferior
VEP--Visual Evoked Potential; A gross measurement using electrodes external to the eye, frequently using a location on the scalp as a voltage or current reference point
Vitamin A--IUPAC-IUB (1982) states: "The term vitamin A should be used as the generic descriptor for retinoids exhibiting qualitatively the biological activity of retinol." More generally, it is known as a fat soluble vitamin described chemically as retinol. Retinol is a lipid and can also be described as a fatty acid. It contains a long carbon chain ending in a carboxyl group. Depending on application, it can be described as:
1. Nutrition--A coenzyme
2. Physiology--A hormone
3. Dye Chemistry--The prototype of a group of retinoids
4. Vision--A chromogen of the chromophores of vision
Vinylene residue--A minimal conjugated carbon chain consisting of two carbons, (C--C==).
Young-Helmholtz Theory--The most prevalent name for the "Trichromatic theory" of color vision; Young first hypothesized the three photoreceptors to be red, yellow and blue (1801) but proposed red, green and blue a year later.
Weber's Law-- Just noticeable increment of stimulus is a constant fraction of stimulus; based on work in the tactile sensations (The Science of Color) expressed as L/L=k by Bartleson. [See Fechner's Law]
Zwitterion--An amino acid in solution normally existing in a dipolar configuration but subject to the pH of the solution.