Vision

Question 0

Describe general photoreceptors.

What are the two specific types?

Answer 0

Receptor cells in the retina that transduce light into action potentials

Rods and cones

Question 1

What portion of the EM spectrum can the human eye detect?

Answer 1

380-760

Question 2

Describe Rods

Answer 2

receptors that respond to low intensity light, such as at night

Question 3

Cones

Answer 3

Photoreceptor that is sensitive to different light intensities. Responsible for color vision and high acuity vision. Daytime vision

Question 4

What is the retina, where is it located?

Answer 4

The retina is neural tissue that contains photoreceptors. It is located on the inner surface of the posterior eye

Question 5

Where is the fovea?

Function?

Answer 5

The fovea is located in the central region of the retina. It is made specifically of cones and is responsible for mediating most acute vision.

Question 6

Optic Disk

Answer 6

Location of exit point from the retina for fibers of ganglion cells that make up optic nerve. Forms a blind spot that we dont perceive

Question 7

What are photopigments?

Answer 7

special molecules imbedded in the membrane of rods and cones that is responsible for transduction of visual info.

Question 8

What is the photopigment in rods?

Answer 8

rhodopsin.

Question 9

What is the photopigment in cones?

Answer 9

three classes of cone opsins: the basis of color vision

Question 10

What happens when light activates a rhodopsin molecule?

Answer 10

Retinaldehyde dissociates from opsin revealing an enzymatic site on the opsin molecule. Combines rapidly with many molecules of G protein transducin…. long cascade of events. Ultimately results in change in membrane potential that results in glutamate release

Question 11

describe rod/cone photoreceptors at resting potential

Answer 11

They steadily release glutamate. Light always hyper-polarizes the photoreceptors

Question 12

Bipolar cells response to glutamate differ. Why?

Answer 12

They have different receptors. Glutamate depolarizes one group of bipolar cells but hyper-polarizes another. Differ by receptive field.

Question 13

How does light close sodium channels in photoreceptors?

Answer 13

Light causes rhodopsin and RETINAL to unbind. This allows opsin to combine rapidly with the G protein transducin. Transducin acts through an enzyme, phosphodiesterase (PDE) to turn cGMP into 5’GMP. cGMP holds sodium channels open. Therefore, as transducin and PDE turn cGMP into 5’ GMP, sodium channels close. This results in hyperpolarization

Question 14

What is the relationship between light, glutamate, and off-center bipolar cells?

Answer 14

Off-Center bipolar cells are excited when light is turned off. It receives more glutamate which depolarizes the off center cells.

Question 15

What is the relationship between on-center bipolar cells, light, and glutamate?

Answer 15

Turning on a light in the center of on-center bipolar cells excites them. They receive less glutamate which otherwise inhibits the on-center cell

Question 16

Bipolar cells release glutamate that always excites the ganglionic cells. How are on-center/off-center ganglionic cells stimulated?

Answer 16

On-Center bipolar cells are stimulated in response to light. Their stimulation leads to the stimulation of on-center ganglionic cells.

Off-Center bipolar cells are stimulated when light is turned off. Their stimulation results in depolarization of off-center ganglionic cells

Question 17

What contacts do the horizontal cells make in the retina?

Do they have action potentials?

Answer 17

photoreceptors and bipolar cells.

No, only ganglionic cells have action potentials.

Question 18

What contacts to amacrine cells have?

Answer 18

They are in contact with bipolar and ganglionic cells.

FYI: All cell types except ganglionic generate graded potentials. (ganglionic fire APs)

Question 19

describe the scotopic visual system.

Answer 19

The scotopic system works in dim light and involves rods. There is highly convergent processing. Very little differentiation between wavelengths of light (all cats are gray at night). High convergence means that many rods converge onto few bipolar cells which converge to one ganglion cell. peripheral vision

Question 20

Describe the photopic system

Answer 20

The photopic system requires more light and involves more detailed processing. Differentiates wavelengths, color vision. High acuity, Low convergence.

Question 21

Describe how sensory info gets from ganglion to brain. Where does the info go?

Answer 21

Optic nerve splits at the optic chiasm. The nerve from each eye sends fibers to both sides of the brain. After the optic chiasm, optic nerves are referred to as the optic tract. Most axons of the optic tract terminate at the lateral geniculate nucleus (visual part of thalamus). What about the superior colliculus and area V1?

Question 22

Describe small ganglion cells.

Answer 22

They have input from single cones. They project to the parvocellular layer of the LGN and discriminate color.

Question 23

What are large ganglion cells?

Answer 23

They are cells that receive input from many cones. They project onto the magnocellular layer of the LGN which can not discriminate color.

Question 24

What do simple cortical cells do? What is their nickname?

Answer 24

Theyre called bar or edge detectors. They respond to an edge or bar of particular width, orientation, and location

Question 25

These cells respond to a bar of particular width and orientation, but may be located within a larger area of the visual field.

Answer 25

complex cortical cells.

Question 26

Area V1

Answer 26

neurons in V1, the primary visual cortex, seem to be involved in the perception of objects as well as the production of mental images.

Question 27

trichromatic hypothesis of color perception

Answer 27

Helmholtz predicted that three types of cones are present and that each would be tuned to its part of the spectrum. Said that each has its own pathway to the brain.

Question 28

Opponent process hypothesis of color perception

Answer 28

Hering argued that there are four uniquers hues and three opposite pairs of colors. Said three systems that produce opposite responses due to different wavelengths.

Question 29

Define the current color vision hypothesis

Answer 29

cones are trichromatic
Ganglion cells are of the opponent process
Humans and primates have three types of cones that are sensitive to differing wavelengths are a result of opsin. Color blind is usually missing opsin for one of three cones.

Question 30

What is protanopia

Answer 30

confusion of red and green.

Question 31

Provide wavelengths that short, medium, and long cones respond to

Answer 31

short: peak sensitivity at 420 nm
medium: 530nm
Long-560 nm

Question 32

What are red-Green cells

Answer 32

Type 1: Red Green cells are excited by red light but inhibited by green light. or vice versa

Question 33

Yellow-Blue cells

Answer 33

Type 2: yellow blue cells are either stimulated or inhibited by yellow or blue light

Question 34

The striate cortex performs additional processing of visual info. Like what?

Answer 34

Orientation and movement.
edge detection
patterns
color

Question 35

Describe the three types of cells that detect orientation and movement in the striate cortex

Answer 35

Simple cells respond to line in a particular orientation
Complex cells respond to a line in a particular orientation that moves
Hypercomplex cells respond to the end of the line of particular orientation

Question 36

What sends information to the visual association cortex

Answer 36

striate cortex