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Neuro Unit 4 > Visual System II > Flashcards

Visual System II Flashcards

1
Q

Photoreceptor cells are located in the

A

outer layer of the retina, nearest the choroid/sclera

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2
Q

For light to reach the photoreceptor cells it must pass through

A

the inner layer of cells (unmyelinated axons)

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3
Q

At the fovea, the inner layer

A

is shifted laterally to directly expose the photoreceptor cells

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4
Q

Pigmented epithelial cells contain

A

melanin

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5
Q

Pigmented epithelial cells function

A

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

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6
Q

Outer segment of a photoreceptor

A

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

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7
Q

Inner segment of a photoreceptor

A

contains the nucleus and metabolic machinery

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8
Q

Synaptic terminal of a photoreceptor

A

transmits signal to next neuron

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9
Q

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

A

rhodopsin

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10
Q

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

A

cone pigments

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11
Q

The outer segment is made up of

A

membranous discs arranged differently to vary the SA

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12
Q

Photopigment molecule is composed of

A

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

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13
Q

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

A

aldehyde of Vitamin A

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14
Q

What determines the properties of the 3 types of cones?

A

opsin molecule and the wavelength it filters

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15
Q

In the dark, the retinal molecule exists as

A

11-cis-retinal

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16
Q

When light strikes the retinal molecule

A

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

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17
Q

11-cis configuration

A

dark; binds opsin and inhibits the protein

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18
Q

11-trans configuration

A

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

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19
Q

Phosphodiesterase activation

A

activated opsin binds TRANSDUCIN and activates phosphodiesterase enzyme

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20
Q

Degradation of cGMP

A

Phosphodiesterase metabolizes cGMP, lowering its intracellular concentration

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21
Q

cGMP levels are high

A

in the DARK

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22
Q

Low intracellular levels of cGMP cause

A

closure of of cGMP channels, reducing the depolarizing current

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23
Q

Reduced depolarizing currents causes

A

HYPERPOLARIZATION of the cell

24
Q

Light ultimately results in

A

hyperpolarization

25
Q

Viagra is a

A

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

26
Q

Dark Current

A

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

27
Q

Hyperpolarization due to light has what effect at the synaptic terminal

A

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

28
Q

In the dark

A

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

29
Q

The brighter the light, the

A

fewer NT’s released

30
Q

By decreasing the NT released (during light)

A

this inhibits the inhibitory effect and causes generation of an AP

31
Q

Bipolar cells become excited causing a

A

graded potential to generate

32
Q

Ganglion cells cause

A

Action potential sent to visual cortex

33
Q

Rhodopsin

A

rod photopigment, responds to all wavelengths

34
Q

Cone Pigments

A

cone photopigments, filter certain wavelengths of light

35
Q

Color depends on

A

the ratio of stimulated cone pigments in response to different wavelengths

36
Q

Cone = sharp image

A

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

37
Q

Can cones summate?

A

NO, no convergence on bipolar cells

38
Q

Rods = convergence

A

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

39
Q

RODS

A

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

40
Q

CONES

A

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

41
Q

Color blindness

A

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

42
Q

Red-green color blindness

A

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

43
Q

Bipolar cells

A

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

44
Q

Ganglion cells

A

fire AP from bipolar cell through optic n

45
Q

Amacrine and Horizontal cells

A

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

46
Q

Vertical flow of information

A

photoreceptors–>bipolar–>ganglion

47
Q

Horizontal flow of information

A

horizontal cell and amacrine cells modulating bipolar responses and graded potentials

48
Q

Ganglion cells are always firing so how is light depicted

A

change in AP firing rate

49
Q

Receptive field of a ganglion cell

A

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

50
Q

A large receptive field =

A

low visual acuity

51
Q

Receptive field on- and off-center

A

composed of a circular center and the surrounding

52
Q

On-center ganglion cells fire ______ in the dark

A

INFREQUENTLY; respond to light to the center of the field

53
Q

Off-center ganglion cells fire when

A

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

54
Q

ON- and OFF- center ganglion cells function to

A

determine edges especially in low light

55
Q

Optic nerve projects to

A

Lateral Geniculate Nucleus

56
Q

The lateral geniculate nucleus then projects to

A

Primary visual cortex

57
Q

Primary Visual Cortex

A

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

Neuro Unit 4 (12 decks)

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