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Neurobiology > Chapter 9: The Eye > Flashcards

Chapter 9: The Eye Flashcards

1
Q

Retina:

A

the back of the eye that contains photoreceptors specialized to convert light energy into neural activity

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2
Q

What part of the eye is able to distinguish light intensity? How?

A

retina

contained two overlapping retinas; one specialized for low light and the other for high light color detection

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3
Q

Light rays travel in straight lines until they interact with the atoms and molecules of the atmosphere:

  1. […]
  2. […]
  3. […]
A
  1. reflection
  2. absorption
  3. refraction
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4
Q

Define the following:

Reflection–

Absorption–

Refraction–

A

Re: bouncing of light rays at angles
Ab: transfer of light energy to a particle or surface
Ra: bending of light rays that occurs

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5
Q

Blue pigment absorbs long wavelengths but […]. This is because some compounds absorb light energy in only a […] range of wavelengths, and reflect the […] wavelengths.

A

reflects short waves; limited; remaining

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6
Q

During refraction, different mediums change the […].

A

speed of light

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7
Q

The greater the difference between the speed of light…

A

the greater the angle of refraction

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8
Q

Optics:

A

the study of light rays and their interactions

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9
Q

Pupil:

A

opening that allows light to enter the eye and reach the retina

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10
Q

Why is the pupil dark?

A

because of the light-absorbing pigments

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11
Q

The pupil is surrounded by the […].

A

iris

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12
Q

Iris:

A

pigmentation provides eye color

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13
Q

How does the pupil change size?

A

the iris contains two muscles which change the size

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14
Q

Cornea:

A

glassy covering of the eye that covers both the iris and pupil

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15
Q

The cornea is continuous with the […].

A

sclera

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16
Q

Sclera:

A

white of the eye that forms a tough wall of the eyeball

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17
Q

The sclera sits on the […]

A

eyes orbit (bony eye socket)

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18
Q

Extraocular muscles:

A

consists of three pairs which move the eyeball in orbit

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19
Q

The extraocular muscles are inserted into the […] and it lies behind the […].

A

sclera; conjuctive

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20
Q

Cojunctiva:

A

membrane folds back from the inside the eyelids and attaches to the sclera

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21
Q

Optic nerve: carrying […] from the […] and exits the back of the eye.

A

axons; retina

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22
Q

The optic nerve passes through the […] and reaches the base of the brain near the […].

A

orbit; pituitary gland

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23
Q

What is the optic disk? What is the significance of this region of the eye?

A

where the optic nerve fibers exit the retina

there are no photoreceptors and thus no perception of light

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24
Q

The cross-sectional view shows the […] taken by light as it passes through the […] towards the retina.

A

path; cornea

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25
Q

Cornea lacks […] so it receives nourishment from the […] of the […]..

A

blood vessels; fluid; aqueous humor

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26
Q

Aqueous humor description:

A

watery fluid that lies between the cornea and the lens

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27
Q

Vitreous humor description:

A

viscous, jellylike that lies between the lens and the retina

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28
Q

What is the significance of vitreous humor?

A

contains the pressure that keeps the eyeball spherical

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29
Q

What separates the two fluids of the eye?

A

lens

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30
Q

Lens:

A

transparent feature located behind the iris

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31
Q

The lens is suspended by […] called […] fibers that are attached to […].

A

ligaments; zonule; ciliary muscles

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32
Q

Ciliary muscles are attached to the […] and form a […] inside the eye.

A

sclera; ring

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33
Q

Refraction is done by what eye feature?

A

cornea

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34
Q

As light passes into a medium where its speed is slowed it will…

A

bend towards a line that is perpendicular to the border, or interface between the media

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35
Q

Focal distance:

A

the distance from the refractive surface to the point where parallel light rays converge

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36
Q

Focal distance depends on the […] of the […]. The tighter the […] the […] the focal distance.

A

curvature; cornea/lens; curve; shorter

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37
Q

Diopter:

A

unit of measurement for refractive power

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38
Q

Formula: Refractive power:

A

1 / focal distance (m)

Units: diopter

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39
Q

The cornea has a refractive power of […].

What is the focal distance? What does this mean in terms of focus?

A

42 diopters

0.024 m; the light rays will be focused 0.024 m behind the corneal surface

**distance from the cornea to the retina

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40
Q

Refractive power depends on the […] of light at the […] interface.

A

slowing; air-cornea

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41
Q

Besides the cornea, what other feature contributes to the eye’s refraction? How so?

A

lens

accommodation

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42
Q

The lens is involved in forming crisp images of objects located…

A

closer than about 9 m from the eye

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43
Q

Accommodation:

A

process of changing the shape of the lens; adding greater refractory power to bring diverging rays into focus

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44
Q

How is accommodation accomplished?

A

contracting and relaxing of the ciliary muscles

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45
Q

During accommodation, the ciliary muscle […] and […] in size, thereby making the area inside the muscle […] and […] the tension in the suspensory ligaments.

Consequently, the lens becomes […] because of its natural […].

This rounding […] the curvature of the […] surface, and […] refractory power.

A

contracts; swells; smaller; decreasing

rounder and thicker; elasticity

increases; lens; increases

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46
Q

Relaxation of the ciliary muscle […] the tension in the suspensory ligaments, and the lens is […] into a […] shape.

A

increases; stretched; flatter

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47
Q

What does the pupil do for optical function?

A

continuously adjusts for different ambient light levels

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48
Q

Pupillary light reflex:

A

control of the pupils constricting muscles by the connections between the retina and the neurons of the brain stem

49
Q

What does it mean by the pupillary light reflex is consensual?

A

both eyes will change in pupil size even though only one eye has light shined at it

50
Q

When the pupillary light reflex is not consensual, what does it indicate?

A

neurological disorders (brainstem)

51
Q

Constriction of the pupil effect increases…

A

depth of focus

52
Q

Visual acuity:

A

ability of the eye to distinguish two nearby points

53
Q

What greatly factors in on visual acuity?

A

the spacing of photoreceptors in the retina and the precision of the eye’s refraction

54
Q

Visual angle:

A

distance across the retina in degrees

55
Q

What is the most direct pathway for visual information to exit the eye?

A

photoreceptors — bipolar cells — ganglion cells — AP — optic nerve — brain

56
Q

What other cell types influence the retinal process?

A
  1. horizontal cells

2. amacrine cells

57
Q

Horizontal cells receive input from the […] and influence surrounding […].

Amacrine cells receive input from the […] and influence surrounding […].

A

photoreceptors; bipolar cells and photoreceptors

bipolar cells; ganglion cells, bipolar cells, and other amacrine cells

58
Q

The only light-sensitive cells in the retina are […]. All others are influenced only by […].

A

photoreceptors; direct/indirect synaptic transmission with photoreceptors

59
Q

The […] are the only source of output from the retina. No other retinal cell type projects an axon through the […].

A

ganglion cells; optic nerve

60
Q

Cells in the retina are organized in […].

A

layers

61
Q

Light must pass from the vitreous humor through the […] and […] before it reaches the […].

A

ganglion cells; bipolar cells; photoreceptors

62
Q

In order to reach the photoreceptors, light must pass through retinal cells. How come there is no distortion of images?

A

retinal cells are transparent

63
Q

List the layer organization of the retinal cells (from innermost to outermost) and include amacrine/horizontal:

A
  1. ganglion cell
  2. inner plexiform
    * *AMACRINE CELLS
  3. inner nuclear layer
    * *HORIZONTAL CELLS
  4. outer plexiform layer
  5. outer nuclear layer
  6. layer of photoreceptor outer segments
  7. pigmented epithelium
64
Q

The inside-out arrangement is advantageous because…

  1. […]
    a. […]
    b. […]
    * * […]
A
  1. pigmented epithelium is below the photoreceptors
    a. plays a critical role in the maintenance of the photoreceptors
    b. absorbs any light that passes entirely through the retina
    * *minimizes reflection of the light
65
Q

What is within the inner nuclear layer?

A

contains the cell bodies of bipolar cells, amacrine cells, and horizontal cells

66
Q

What is within the outer nuclear layer?

A

cell bodies of the photoreceptors

67
Q

What is within the layer of photoreceptor outer segments?

A

light-sensitive elements of the retina

68
Q

What is within the inner plexiform layer?

A

contains synaptic contacts between bipolar cells, amacrine cells, ganglion cells

69
Q

What is within the outer plexiform layer?

A

photoreceptors make synaptic contact with the bipolar and horizontal cells

70
Q

Four regions of every photoreceptor:

A
  1. outer segment
  2. inner segment
  3. cell body
  4. synaptic terminal
71
Q

What are the two types of photoreceptors? How do they differ from one another?

R (5)
C (4)

A
  1. rods
  2. cones

R:

  1. greater number of disks
  2. higher photopigment concentration
  3. 1000 times more sensitive to light than cones
  4. only contributor to nighttime lighting/scotopic conditions
  5. same photopigment

C:

  1. fewer number of disks
  2. bulk of work during the daytime lighting/photopic conditions
  3. responsible for seeing color
  4. three different types of photopigments
72
Q

Retina is […]– a scotopic retina using only […] and photopic retina using mainly […].

A

duplex; rods; cones

73
Q

What two characteristics does the peripheral retina have that make this arrangement more sensitive to light? Why is this the case?

A
  1. higher ratio of rods to cones
  2. higher ratio of photoreceptors to ganglion cells

SENSITIVE BC

  1. rods specialized in low light
  2. there are more photoreceptors feeding information to each ganglion cell
74
Q

The region of the retina most highly specialized for high resolution is the […].

A

fovea

75
Q

Fovea is a […] of the retina at the center of the […].

In cross-section, the fovea appears as a […]. This is due to the […]. of the cells above the photoreceptors, allowing light to strike the […] without passing through the […] cell layers.

This maximizes visual acuity by […] other cells that might scatter light and blur the image. The central fovea also is unique because it contains no […]; all the photoreceptors are […].

A

thinning; macula

pit; lateral displacement; photoreceptors; retinal

pushing aside; rods; cones

76
Q

TRANSDUCTION IN RODS

Light stimulation of the photopigment activates […] which in turn activates […] that changes the cytoplasmic concentration of a […].

This change causes a membrane ion channel to […] and the […] to change.

A

G-protein; effector enzymes; second messengers

close; membrane potential

77
Q

TRANSDUCTION IN RODS

In complete darkness, the membrane potential of a rod is […]. The reason for this is due to […] through special channels in the […].

A

-30 mV; steady Na+ influx; outer segment

78
Q

TRANSDUCTION IN RODS

Dark current:

A

movement of positive charge across the membrane during the dark

79
Q

TRANSDUCTION IN RODS

Dark current is […] by the intracellular second messenger called […] and is continually produced in the photoreceptor by […] keeping […] channels open.

A

gated; cyclic guanosine monophosphate; enzyme guanylyl cyclase; Na+

80
Q

TRANSDUCTION IN RODS

In rods: Light […] cGMP, cause the Na+ channels to […] and the membrane potential becomes […].

A

reduces; close; more negative

81
Q

TRANSDUCTION IN RODS

Photoreceptors […] in response to light.

A

hyperpolarize

82
Q

TRANSDUCTION IN RODS

The hyperpolarizing response to light is initiated by…

A

the absorption of electromagnetic radiation by the photopigment in the membrane of the stacked disks in the rod outer segments

83
Q

TRANSDUCTION IN RODS

In rods the photopigment that initiates the hyperpolarizing response is […].

A

rhodopson

84
Q

TRANSDUCTION IN RODS

Rhodopsin:

A

receptor protein with a pre-bound chemical agonist

85
Q

TRANSDUCTION IN RODS

What is the receptor protein for rhodopsin?

What is the prebound agonist?

A

opsin

retinal

86
Q

TRANSDUCTION IN RODS

Retinal:

A

derivative of vitamin A

87
Q

TRANSDUCTION IN RODS

The absorption of light causes a change in the conformation of […] so that it activates the […] in opsin. This process is called […].

A

retinal; G-protein complex; bleaching

88
Q

TRANSDUCTION IN RODS

The bleaching of rhodopsin stimulates the G-protein […] in the disk membrane which in turn activates the effect enzyme […].

A

transducin; phosphodiesterase

89
Q

TRANSDUCTION IN RODS

Phosphodiesterase:

A

effector enzyme that breaks down the cGMP

90
Q

TRANSDUCTION IN RODS

The amplification consequence of transduction allows our visual system the ability to detect as little as…

A

a single photon

91
Q

TRANSDUCTION IN CONES

Saturation causes…

A

no more hyperpolarization

92
Q

Vison during the day depends entirely on the […] whose photopigments require […] to become […].

A

cones; more energy (than rods); bleached

93
Q

What is the major difference between the phototransduction in cones vs rods?

A

type of opsins in the membranous disks of the cone outer segments

94
Q

TRANSDUCTION IN CONES

What are the three different types of opsins/photopigments for cones?

A

blue, green, red

95
Q

TRANSDUCTION IN CONES

When are the cone opsins maximally activated?

A

B: 430 nm
G: 530 nm
R: 560 nm

96
Q

TRANSDUCTION IN CONES

Young-Helmholtz trichromacy theory:

A

the theory that the brain assigns colors based on a comparison of the readout of the three types of cone photoreceptors

97
Q

TRANSDUCTION IN CONES

The peak sensitivity of the rods is to a wavelength of about […] perceived as […].

A

500 nm; blue-green

98
Q

The transition from all-cone daytime vision to all-rod nighttime vision is not […] it takes about […] minutes.

A

instantaneous; 20-25

99
Q

Dark adaption:

A

getting used to the dark

100
Q

How can dark adaption be explained?

A
  1. dilation of the pupil allows more light to enter

2. light adaption

101
Q

Light adaption:

A

reversing the changes in the retina that accompanied dark adaption

102
Q

What concentration is a factor in the eye’s ability to adapt to changes in light?

A

calcium

103
Q

When you step out into bright light from a dark theater, initially the cones are […].

The […] helps a bit in reducing the light entering the eye. However, the most important change is the gradual […] of the membrane back to about […].

A

hyperpolarized

constriction of the pupil; depolarization; -35 mV.

104
Q

Only […] cells fire action potentials in the retina. All other cells respond to […] when […] changes in membrane potential.

A

ganglion; stimulations; graded

105
Q

The most direct path for information flow in the retina:

A

cone photoreceptor—bipolar cell—ganglion cell

106
Q

At each synaptic relay, the responses are modified by… (2)

A
  1. lateral connections of horizontal cells

2. lateral connections of amacrine cells

107
Q

What NT is released when a photoreceptor is depolarized?

A

AA glutamate

108
Q

Photoreceptors are […] in the dark and are […] in the light.

A

depolarized; hyperpolarized

109
Q

In the outer plexiform layer, each photoreceptor is in synaptic contact with two types of retinal neuron:

How is each significant?

A
  1. bipolar cells
  2. horizontal cells

B: creat direct pathway from photoreceptors to ganglion cells
H: influence laterally in the plexiform layer; influence neighbors

110
Q

What are the two classifications of bipolar cells? What is this based on?

A
  1. OFF bipolar cells
  2. ON bipolar cells

their responses to the glutamate released by photoreceptors

111
Q

In OFF bipolar cells what occurs?

A

glutamate-gated cation channels mediate a classical depolarizing EPSP from the influx of Na+

112
Q

In ON bipolar cells, what occurs?

A

G-protein coupled receptors respond to glutamate hyperpolarizing

113
Q

Light off means […] glutamate. More light means […] glutmate.

A

more; less

114
Q

The number of photoreceptors in this cluster ranges from… (2)

A
  1. one at the center of the fovea

2. thousands in the peripheral retina

115
Q

Receptive field:

A

is the area of retina that, when stimulated with light, changes the cell’s membrane potential

116
Q

What are the two parts of the receptive field of a bipolar cell?

A
  1. receptive field center: circular area providing direct photoreceptor input
  2. receptive field surround: surrounding area of retina providing input via horizontal cells
117
Q

One mm of the retina corresponds with a visual angle of …

A

about 3.5

118
Q

Which group of bipolar cells have a larger receptive field diameter?

A

the peripheral retina (the receptive field is a fraction of a degree compared to several degrees)

119
Q

Center-surround receptive fields:

A

a visual receptive field with a circular center region + surround region = ring around the center

stimulation of the center produces a response opposite that generated by stimulation of the surround

** why it’s antagonistic

Neurobiology (12 decks)

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