CHAPTER 10: VISION

Question 1

What is wavelength?

Answer 1

Related to perception of color / hue

Question 2

What is amplitude?

Answer 2

related to perception of brightness

Question 3

Pupil

Answer 3

Opening where light enters the eye

Question 4

Iris

Answer 4

Controls the size of the pupil; gives color to the eyes

Question 5

Cornea

Answer 5

Glassy transparent external surface of the eye; covers iris and pupil

Question 6

Sclera

Answer 6

White part of the eye; tough wall of eyeball

Question 7

Optic Nerve

Answer 7

Bundle of axons from the retina

Question 8

Optic Disc

Answer 8

Blood vessels enter, optic nerve exits

Question 9

Macula

Answer 9

Central vision / area around fovea

Question 10

Fovea

Answer 10

Pit at center of retina; area of clearest vision

Question 11

Macular Degeneration

Answer 11

leading cause of blindness in old age

Question 12

Lens

Answer 12

Responsible for image formation and accommodation

Question 13

Accommodation

Answer 13

The changing of shape of lens that allows for extra focusing power

Question 14

Pupil

Answer 14

controls the amount of light that enters the eye (expands in dim light, constricts in bright light)

Question 15

Pupillary light reflex

Answer 15

continuous adjustment to light travel, uses connection between retina and brain stem neurons that control muscle around pupil

Question 16

Visual Field

Answer 16

Amount of space viewed by the retina when the eye is fixated straight ahead

Question 17

Visual acuity

Answer 17

ability to distinguish two nearby points; sharpness/clarity of vision

Question 18

Visual angle

Answer 18

distances across the retina described in degrees

Question 19

Retina

Answer 19

Photoreceptors (rods and cones) are the transducers, ganglion cells carry output; axons from optic nerve, has five cell types that are arranged in layers

Question 20

What are the five cell types of the Retina?

Answer 20

• ganglion cells
• Amacrine cells
• Bipolar cells
• Horizontal cells
• photoreceptors (cones and rods)

Question 21

Direct (vertical) pathway of the cells in Retina

Answer 21

Photoreceptors to bipolar cells to ganglion cells which project to the forebrain

Question 22

Horizontal cells

Answer 22

receive input from photoreceptors and project to other photoreceptors and bipolar cells

Question 23

Amacrine cells

Answer 23

receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells

Question 24

Rods

Answer 24

• have rectangular segments
• handle scotopic (night) vision
• stop working in bright light

Question 25

Cones

Answer 25

- have pointed segment - handle (photopic (daytime) vision - three types, each with their own pigment sensitive to different wavelengths

Question 26

Photoreceptors

Answer 26

- convert light to neural signals - outer segments contain photopigment; only part of the eye that is sensitive to light

Question 27

Macula

Answer 27

- has most of the discs - fovea is packed with tiny cones, each with its own ganglion cell - clear vision, color vision

Question 28

Peripheral retina

Answer 28

- mostly rods - many photoreceptors converge on a single ganglion cell - more sensitive to light - detects motion

Question 29

Fovea

Answer 29

- maximizes visual acuity - central fovea = all cones and area of highest visual acuity

Question 30

Phototransduction in Rods

Answer 30

1. light changes retinals shape, deforming the rhodopsin to activate about 500 molecules of the G protein transducin - this activation causes a GTP molecule to replace a GDP molecule bound to transducin 2. The activated transducins activate PDE molecules 3. Each PDE molecule hyper polarizes, reducing its concentration 4. Closure of Na+ channels and hyper polarization of the receptor - Photoreceptors hyper polarize in response to light, because light closes Na+ channels - photoreceptors depolarize in the absence of light

Question 31

Phototransduction in cones

Answer 31

- similar to rods - different proteins involved: opsins - tuned to red, green, blue - population coding

Question 32

Receptive fields

Answer 32

stimulation in a small part of the visual field changes a cell's membrane potential - center : connections to bipolar cells - surround : indirect connections via horizontal cells

Question 33

ON center bipolar cells

Answer 33

uses G - protein receptors and depolarizes when light is on (releases more Glu into ganglion cells)

Question 34

OFF center bipolar cells

Answer 34

uses Glu gated ion channels and depolarizes when light is off (releases less Glu into ganglion cells)

Question 35

Pathway of bipolar cells

Answer 35

receptor, bipolar cell, ganglion cell

Question 36

Process of light hitting bipolar cell

Answer 36

- photoreceptor releases glutamate when is depolarized - photoreceptor connects to both ON and OFF bipolar cells - bipolar cells connect to same type ganglion cells (ON & ON or OFF & OFF) - ON and OFF bipolar cells respond to glutamate in opposite ways

Question 37

How do ON bipolar cells respond to glutamate?

Answer 37

have metabotropic receptors and hyperpolarize to glutamate

Question 38

How do OFF bipolar cells respond to glutamate ?

Answer 38

have ionotropic receptors and depolarize to glutamate

Question 39

Ganglion cell receptive fields

Answer 39

- tuned to detect light in specific locations - generate APs when depolarized

Question 42

OFF center ganglion cell

Answer 42

black dot detector

Question 43

ON center ganglion cell

Answer 43

white dot detector

Question 44

What is the difference between bipolar and ganglion cells

Answer 44

bipolar cells generate graded local potentials whereas ganglion cells generate action potentials