Chapter 2: The First Steps in Vision - From Light to Neural Signals Flashcards
wave
An oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium.
photon
A quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties.
absorb
To take up something – such as light, noise or energy – and not transmit it at all.
scatter
To disperse something – such as light – in an irregular fashion.
reflect
To redirect something that strikes a surface – especially light, sound or heat – usually back toward its point of origin.
transmit
To convey something (e.g., light) from one place or thing to another.
refract
- To alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from the air.
- To measure the degree of refraction in a lens or eye.
image
A picture or likeness.
cornea
The transparent “window” into the eyeball.
transparent
Allowing light to pass through with no interruption, so that objects on the other side can be clearly seen.
aqueous humor
The watery fluid in the anterior chamber of the eye.
lens
The lens inside the eye that enables the changing of focus.
pupil
The dark, circular opening at the center of the iris in the eye, where light enters the eye.
iris
The colored part of the eye, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil.
vitreous humor
The transparent fluid that fills the vitreous chamber in the posterior part of the eye.
retina
A light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve.
emmetropia
The condition in which there is no refractive error, because the refractive power of the eye is perfectly matched to the length of the eyball.
diopter (D)
A unit of measurement of the optic power of a lens. It is equal to the reciprocal of the focal length, in meters. A 2-diopter lens will bring parallel rays of light into focus at 1/2 meter (50cm).
myopia
Nearsightedness,a common condition in which light entering the eye is focused in front of the retina and distant objects cannot be seen sharply.
hyperopia
Farsightedness, a common condition in which light entering the eye is focused behind the retina and accommodation is required in order to see near objects clearly.
astigmatism
A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.
accommodation
The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).
presbyopia
Literally “old sight.” The age-related loss of accommodation, which makes it difficult to focus on near objects.
cataract
An opacity of the crystalline lens.
transduce
To convert from one form of energy to another (e.g., from light to neural electrical energy, or from mechanical movement to neural electrical energy.
fundus
The back layer of the retina; what the eye doctor sees through an ophthalmoscope.
photoreceptor
A light-sensitive receptor in the retina.
rod
A photoreceptor specialized for night vision.
cone
A photoreceptor specialized for daylight vision, fine visual acuity, and color.
duplex
In reference to the retina, consisting of two parts; the rods and cones, which operate under different conditions
fovea
A small pit, near the center of the macula, that contains the highest concentration of cones, and no rods. It is the portion of the retina that produces the highest visual acuity and serves as the point of fixation.
eccentricity
The distance between the retinal image and the fovea.
outer segment
The part of a photoreceptor that contains photopigment molecules.
inner segment
The part of a photoreceptor that lies between the outer segment and the cell nucleus.
synaptic terminal
The location where axons terminate at the synapse for transmission of information by the release of a chemical transmitter.
chromophore
The light-catching part of the visual pigments of the retina.
rhodopsin
The visual pigment found in rods.
melanopsin
A photopigment that is sensitive to ambient light.
photoactivation
Activation by light.
hyperpolarization
An increase in membrane potential such that the inner membrane surface becomes more negative than the outer membrane surface.
graded potential
An electrical potential that can vary continuously in amplitude.
horizontal cell
A specialized retinal cell that contacts both photoreceptor and bipolar cells.
lateral inhibition
Antagonistic neural interaction between adjacent regions of the retina.
amacrine cell
A retinal cell found in the inner synaptic layer that makes synaptic contacts with bipolar cells, ganglion cells, and other amacrine cells.
bipolar cell
A retinal cell that synapses with other rods or cones (not both) and with horizontal cells, and then passes the signals on to ganglion cells.
diffuse bipolar cell
A bipolar retinal cell whose processes are spread out to receive input from multiple cones.
sensitivity
- The ability to perceive via the sense organs.
- Extreme responsiveness to radiation, especially to light of a specific wavelength.
- The ability to respond to transmitted signals.
visual acuity
A measure of the finest detail that can be resolved by the eyes.
midget bipolar cell
A small bipolar cell in the central retina that receives input from a single cone.
ON bipolar cell
A bipolar cell that responds to an increase in light captured by the cones.
OFF bipolar cell
A bipolar cell that responds to a decrease in light captured by the cones.
ganglion cell
A retinal cell that receives visual information from photoreceptors via two intermediate neuron types (bipolar cells and amacrine cells) and transmits information to the brain and midbrain.
P ganglion cell
A small ganglion cell that receives excitatory input from single midget bipolar cells in the central retina and feeds the parvocellular layer of the lateral geniculate nucleus.
M ganglion cell
A ganglion cell resembling a little umbrella that receives excitatory input from diffuse bipolar cells and feeds the magnocellular layer of the lateral geniculate nucleus.
koniocellular cell
A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.
receptive field
The region on the retina in which visual stimuli influence a neuron’s firing rate.
ON-center cell
A cell that depolarizes in response to an increase in light intensity in its receptive-field center.
OFF-center cell
A cell that depolarizes in response to a decrease in light intensity in its receptive-field center.
filter
An acoustic, electrical, electronic, or optic device, instrument, computer program, or neuron that allows the passage of some frequencies or digital elements ad blocks the passage of others.
contrast
The difference in luminance between an object and the background, or between lighter and darker parts of the same object.
age-related macular degeneration (AMD)
A disease associated with aging that affects the macula. AMD gradually destroys sharp central vision, making it difficult to read, drive, and recognize faces. There are two forms of AMD: wet and dry.
retinitis pignentosa (RP)
A progressive degeeration of the retina that affects night vision and peripheral vision. RP commonly runs in families and can be caused by defects in a number of different genes that have recently been identified.
