Visual System II

Question 1

Photoreceptor cells are located in the

Answer 1

outer layer of the retina, nearest the choroid/sclera

Question 2

For light to reach the photoreceptor cells it must pass through

Answer 2

the inner layer of cells (unmyelinated axons)

Question 3

At the fovea, the inner layer

Answer 3

is shifted laterally to directly expose the photoreceptor cells

Question 4

Pigmented epithelial cells contain

Answer 4

melanin

Question 5

Pigmented epithelial cells function

Answer 5

to absorb excess light not captured by the photreceptors to prevent light reflected back (reducing sharpness)

Question 6

Outer segment of a photoreceptor

Answer 6

light-sensitive portion (nearest choroid), signal transduction occurs here

Question 7

Inner segment of a photoreceptor

Answer 7

contains the nucleus and metabolic machinery

Question 8

Synaptic terminal of a photoreceptor

Answer 8

transmits signal to next neuron

Question 9

Outer segment of a photoreceptor contains photopigments, in rods these are called

Answer 9

rhodopsin

Question 10

Outer segment of a photoreceptor contains photopigments, in cones these are called

Answer 10

cone pigments

Question 11

The outer segment is made up of

Answer 11

membranous discs arranged differently to vary the SA

Question 12

Photopigment molecule is composed of

Answer 12

retinal (light-absorbing) part and a opsin (protein)

Question 13

The retinal portion of the photopigment is made of ______ in all 4 types of photopigments

Answer 13

aldehyde of Vitamin A

Question 14

What determines the properties of the 3 types of cones?

Answer 14

opsin molecule and the wavelength it filters

Question 15

In the dark, the retinal molecule exists as

Answer 15

11-cis-retinal

Question 16

When light strikes the retinal molecule

Answer 16

conformational change occurs from 11-cis to 11-trans-retinal

Question 17

11-cis configuration

Answer 17

dark; binds opsin and inhibits the protein

Question 18

11-trans configuration

Answer 18

light; no longer binds and inhibits opsin, activating the opsin molecule

Question 19

Phosphodiesterase activation

Answer 19

activated opsin binds TRANSDUCIN and activates phosphodiesterase enzyme

Question 20

Degradation of cGMP

Answer 20

Phosphodiesterase metabolizes cGMP, lowering its intracellular concentration

Question 21

cGMP levels are high

Answer 21

in the DARK

Question 22

Low intracellular levels of cGMP cause

Answer 22

closure of of cGMP channels, reducing the depolarizing current

Question 23

Reduced depolarizing currents causes

Answer 23

HYPERPOLARIZATION of the cell

Question 24

Light ultimately results in

Answer 24

hyperpolarization

Question 25

Viagra is a

Answer 25

phosphodiesterase inhibitor (class V cGMP selective) --> visual disturbances

Question 26

Dark Current

Answer 26

all cGMP channels are open resulting in an inward current and slight depolarization of the cell of (-40mV)

Question 27

Hyperpolarization due to light has what effect at the synaptic terminal

Answer 27

causes voltage-gated-Ca channels to close, reducing Ca influx, and reduced number of NT's released from the synaptic terminal

Question 28

In the dark

Answer 28

high levels of cGMP, depolarized (-40mV), open Ca channels, high level NT released

Question 29

The brighter the light, the

Answer 29

fewer NT's released

Question 30

By decreasing the NT released (during light)

Answer 30

this inhibits the inhibitory effect and causes generation of an AP

Question 31

Bipolar cells become excited causing a

Answer 31

graded potential to generate

Question 32

Ganglion cells cause

Answer 32

Action potential sent to visual cortex

Question 33

Rhodopsin

Answer 33

rod photopigment, responds to all wavelengths

Question 34

Cone Pigments

Answer 34

cone photopigments, filter certain wavelengths of light

Question 35

Color depends on

Answer 35

the ratio of stimulated cone pigments in response to different wavelengths

Question 36

Cone = sharp image

Answer 36

1:1 cone:bipolar cell, increases sharpness BUT LOWERS threshold

Question 37

Can cones summate?

Answer 37

NO, no convergence on bipolar cells

Question 38

Rods = convergence

Answer 38

1:100 bipolar cell: rod; poor sharpness, BUT HIGHER sensitivity (due to summation)

Question 39

RODS

Answer 39

high sensitivity, decreased sharpness; more photopigment, low threshold, low clarity, easily saturated, achromatic

Question 40

CONES

Answer 40

high sharpness, decreased sensitivity; less photopigment, less saturation, high clarity, chromatic

Question 41

Color blindness

Answer 41

inability to perceive differences in colors, genetic, photopigment absence or mutation

Question 42

Red-green color blindness

Answer 42

mutation in green photopigment causing a shift in the sensitivity toward red light

Question 43

Bipolar cells

Answer 43

connect rods/cones to ganglion cells and only elicit graded potentials

Question 44

Ganglion cells

Answer 44

fire AP from bipolar cell through optic n

Question 45

Amacrine and Horizontal cells

Answer 45

help integrate and modify graded potentials from the bipolar cells to interconnect photoreceptors

Question 46

Vertical flow of information

Answer 46

photoreceptors-->bipolar-->ganglion

Question 47

Horizontal flow of information

Answer 47

horizontal cell and amacrine cells modulating bipolar responses and graded potentials

Question 48

Ganglion cells are always firing so how is light depicted

Answer 48

change in AP firing rate

Question 49

Receptive field of a ganglion cell

Answer 49

defined circular area of the retina that a single ganglion cell responds to

Question 50

A large receptive field =

Answer 50

low visual acuity

Question 51

Receptive field on- and off-center

Answer 51

composed of a circular center and the surrounding

Question 52

On-center ganglion cells fire ______ in the dark

Answer 52

INFREQUENTLY; respond to light to the center of the field

Question 53

Off-center ganglion cells fire when

Answer 53

light strikes the periphery, but are inhibited by light on the center of the receptive field

Question 54

ON- and OFF- center ganglion cells function to

Answer 54

determine edges especially in low light

Question 55

Optic nerve projects to

Answer 55

Lateral Geniculate Nucleus

Question 56

The lateral geniculate nucleus then projects to

Answer 56

Primary visual cortex

Question 57

Primary Visual Cortex

Answer 57

Each subdivision responds to a particular direction, color, movement, etc