Chapter 2: The First Steps in Vision - From Light to Neural Signals

Question 1

wave

Answer 1

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.

Question 2

photon

Answer 2

A quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties.

Question 3

absorb

Answer 3

To take up something – such as light, noise or energy – and not transmit it at all.

Question 4

scatter

Answer 4

To disperse something – such as light – in an irregular fashion.

Question 5

reflect

Answer 5

To redirect something that strikes a surface – especially light, sound or heat – usually back toward its point of origin.

Question 6

transmit

Answer 6

To convey something (e.g., light) from one place or thing to another.

Question 7

refract

Answer 7

1. 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.
2. To measure the degree of refraction in a lens or eye.

Question 8

image

Answer 8

A picture or likeness.

Question 9

cornea

Answer 9

The transparent “window” into the eyeball.

Question 10

transparent

Answer 10

Allowing light to pass through with no interruption, so that objects on the other side can be clearly seen.

Question 11

aqueous humor

Answer 11

The watery fluid in the anterior chamber of the eye.

Question 12

lens

Answer 12

The lens inside the eye that enables the changing of focus.

Question 13

pupil

Answer 13

The dark, circular opening at the center of the iris in the eye, where light enters the eye.

Question 14

iris

Answer 14

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.

Question 15

vitreous humor

Answer 15

The transparent fluid that fills the vitreous chamber in the posterior part of the eye.

Question 16

retina

Answer 16

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.

Question 17

emmetropia

Answer 17

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.

Question 18

diopter (D)

Answer 18

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).

Question 19

myopia

Answer 19

Nearsightedness,a common condition in which light entering the eye is focused in front of the retina and distant objects cannot be seen sharply.

Question 20

hyperopia

Answer 20

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.

Question 21

astigmatism

Answer 21

A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.

Question 22

accommodation

Answer 22

The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).

Question 23

presbyopia

Answer 23

Literally “old sight.” The age-related loss of accommodation, which makes it difficult to focus on near objects.

Question 24

cataract

Answer 24

An opacity of the crystalline lens.

Question 25

transduce

Answer 25

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.

Question 26

fundus

Answer 26

The back layer of the retina; what the eye doctor sees through an ophthalmoscope.

Question 27

photoreceptor

Answer 27

A light-sensitive receptor in the retina.

Question 28

rod

Answer 28

A photoreceptor specialized for night vision.

Question 29

cone

Answer 29

A photoreceptor specialized for daylight vision, fine visual acuity, and color.

Question 30

duplex

Answer 30

In reference to the retina, consisting of two parts; the rods and cones, which operate under different conditions

Question 31

fovea

Answer 31

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.

Question 32

eccentricity

Answer 32

The distance between the retinal image and the fovea.

Question 33

outer segment

Answer 33

The part of a photoreceptor that contains photopigment molecules.

Question 34

inner segment

Answer 34

The part of a photoreceptor that lies between the outer segment and the cell nucleus.

Question 35

synaptic terminal

Answer 35

The location where axons terminate at the synapse for transmission of information by the release of a chemical transmitter.

Question 36

chromophore

Answer 36

The light-catching part of the visual pigments of the retina.

Question 37

rhodopsin

Answer 37

The visual pigment found in rods.

Question 38

melanopsin

Answer 38

A photopigment that is sensitive to ambient light.

Question 39

photoactivation

Answer 39

Activation by light.

Question 40

hyperpolarization

Answer 40

An increase in membrane potential such that the inner membrane surface becomes more negative than the outer membrane surface.

Question 41

graded potential

Answer 41

An electrical potential that can vary continuously in amplitude.

Question 42

horizontal cell

Answer 42

A specialized retinal cell that contacts both photoreceptor and bipolar cells.

Question 43

lateral inhibition

Answer 43

Antagonistic neural interaction between adjacent regions of the retina.

Question 44

amacrine cell

Answer 44

A retinal cell found in the inner synaptic layer that makes synaptic contacts with bipolar cells, ganglion cells, and other amacrine cells.

Question 45

bipolar cell

Answer 45

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.

Question 46

diffuse bipolar cell

Answer 46

A bipolar retinal cell whose processes are spread out to receive input from multiple cones.

Question 47

sensitivity

Answer 47

1. The ability to perceive via the sense organs. 2. Extreme responsiveness to radiation, especially to light of a specific wavelength. 3. The ability to respond to transmitted signals.

Question 48

visual acuity

Answer 48

A measure of the finest detail that can be resolved by the eyes.

Question 49

midget bipolar cell

Answer 49

A small bipolar cell in the central retina that receives input from a single cone.

Question 50

ON bipolar cell

Answer 50

A bipolar cell that responds to an increase in light captured by the cones.

Question 51

OFF bipolar cell

Answer 51

A bipolar cell that responds to a decrease in light captured by the cones.

Question 52

ganglion cell

Answer 52

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.

Question 53

P ganglion cell

Answer 53

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.

Question 54

M ganglion cell

Answer 54

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.

Question 55

koniocellular cell

Answer 55

A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.

Question 56

receptive field

Answer 56

The region on the retina in which visual stimuli influence a neuron's firing rate.

Question 57

ON-center cell

Answer 57

A cell that depolarizes in response to an increase in light intensity in its receptive-field center.

Question 58

OFF-center cell

Answer 58

A cell that depolarizes in response to a decrease in light intensity in its receptive-field center.

Question 59

filter

Answer 59

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.

Question 60

contrast

Answer 60

The difference in luminance between an object and the background, or between lighter and darker parts of the same object.

Question 61

age-related macular degeneration (AMD)

Answer 61

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.

Question 62

retinitis pignentosa (RP)

Answer 62

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.