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Neuroscience Exam 2 > Lecture 4: Vision-Retinal Processing > Flashcards

Lecture 4: Vision-Retinal Processing Flashcards

1
Q

What is the region of high visual acuity in the eye?

A

macula/fovea

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2
Q

What is the blindspot of the eye?

A

optic disk

no receptors, this is where cells/axons leave retina to become part of the optic nerve

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3
Q

What is the vascular supply of the eye?

A

branch of opthalmic artery and branch of opthalmic vein

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4
Q

Most of our vision is ____

A

binocular

this is central vision (both eyes)

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5
Q

Most of our peripheral vision is____

A

monocular

one eye

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6
Q

Where is light absorbed?

A

retina

light perception begins at retina

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7
Q

How can the lens accomodate when light info enters?

A

It can change shape so that the light is refracted at the correct angle onto the retina

lens help focus light

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8
Q

To see far, how does the eye accommodate?

A
  1. Ciliary muscle relaxes
  2. suspensory ligament taut
  3. lends flattens/thins
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9
Q

To see near, how does the eye accommodate?

A
  1. Ciliary muscle contracts
  2. Suspensory ligament relaxes
  3. lends become globular (thickens)
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10
Q

What is emmetropia?

A

Normal vision

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11
Q

What is myopia and where is the focal point?

A

near sightedness. focal point is in front of the eye

can see near, focus light in front of the retina,

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12
Q

What is hyperopia and where is the focal point?

A

far-sightedness and the focus behind the retina

can see far, light focuses behind the retina, cant see near

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13
Q

How do glassses/contacts help you see?

A

glasses/contacts changes the angle of light so it reaches the retina

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14
Q

Projections of the visual field/image onto the retina are ____

A

inverted (flipped upside down and backwards)

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15
Q

Visual Field is?

A

What you’re looking at in space

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16
Q

Retinal field is?

A

What’s projected onto the retina

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17
Q

All information from the RIGHT visual field will end up on the ____ portion of the brain.

A

LEFT

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18
Q

How does info from your RIGHT visual field end up on the LEFT side of your brain?

A
  1. Info projects onto temporal regions of LEFT retina and nasal region of RIGHT retina
  2. All info that projects to temporal stays ipsilateral (same side)
  3. All info projected to nasal retina will cross to contralateral side
  4. Then its sent up the LEFT optic tract and LEFT side of brain for processing
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19
Q

All information from the LEFT visual field will end up on the ____ portion of the brain.

A

RIGHT

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20
Q

How does info from your LEFT visual field end up on the RIGHT side of your brain?

A
  1. Info projects onto temporal regions of RIGHT retina and nasal region of LEFT retina
  2. All info that projects to temporal stays ipsilateral (same side)
  3. All info projected to nasal retina will cross to contralateral side
  4. Then its sent up the RIGHT optic tract and RIGHT side of brain for processing
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21
Q

Given that each eye receives information from either visual field, fibers cross at the ____ to get information from the visual field to its respective cortical region.

A

optic chiasm

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22
Q

What are the two types of photoreceptors of the retina?

A

Rods and cones

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23
Q

Where are rods located?

A

retina except optic disk

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24
Q

Where are cones located?

A

Macula/Fovea

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25
Q

What are the 5 retinal neurons?

A
  1. Photoreceptors
  2. Horizontal cells = release GABA (inhibitory) and form gap junctions
  3. Bipolar cell
  4. Amacrine cell = release GABA, glycine, and dopamine (inhibitory) and form gap junctions
  5. Ganglion cell

  • Photoreceptors, bipolar cells, and horizontal cells produce graded potentials
  • Amacrine cells and ganglion cells produce action potentials
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26
Q

Briefly explain how light reaches the retina?

A
  1. Light enters the superficial retina, passes through cell bodies, and travels towards the back in order to reach photosensitive cells (rods and cones).
  2. Action potential allows photoreceptor signaling to be sent back up towards the superficial retina where they can then be guided to the optic nerve and CNS.
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27
Q

What are rods highly sensitive to?

A

Low levels of light

not sensitive to color

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28
Q

What protein do rods have and do they have a large or small number of disks?

A

Opsin=rhodopsin
a large number of disks

  • Rods have far larger areas of photoreceptor disks to make them highly sensitive to light.
  • Opsin responds to light
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29
Q

What are cones sensitive to?

A

Cones are sensitive to colors

30
Q

What protein do cones have and do they have a large or small number of disks?

A

Many (around 3) different opsins
smaller number of disks

different opsins are responsible for detecting different wavelenghts that give us diff colors

31
Q

What is the function of pigment epithelium?

A

It is a “backward” organization of the retinal layer due to the need for constant recycling of photoreceptor proteins (opsins) and disks

Photoreceptors (rods and cones) are embedded in the pigment epithelium

32
Q

Why do we need to recycle photoreceptor proteins and what is required to do so?

on exam

A
  • Need to be constantly synthesizing new proteins so we stay sensitive to light, especially rods (low light conditions).
  • We need VITAMIN A (retinol) which maintains rods and rhodopsin signaling
33
Q

___________ of total body retinol (Vitamin A) is stored in liver

A

50-85%

34
Q

What is scotopic vision?

A

Only rods are being used

like an on/off switch, no wavelength to tell you color

35
Q

What is mesopic vision?

A

Rods and cones are being used

you can see color

36
Q

What is photopic vision?

A

only cones are being used (rods are saturated with light)

rods are saturated with light so much that rods aren’t firing anymore, and we use cones

37
Q

Which type of vision has the best acuity?

A

Photopic vision

bc cone and color info

38
Q

Light sensitivity depends on ____ and ____.

A

receptive field size, intensity

39
Q

Rods are usually activated at what wavelength of light?

A

400-600nm

40
Q

What is trichromat?

A

This is normal vision; you contain all 3 cones subtype

have all 3 opsins

41
Q

What is protanopia?

A

This is a type of colorblindness where you lose the cone subtype responsible for RED wavelengths

2/3 opsins, missing longest=red wavelength of light

42
Q

What is deuteranopia?

A

This is a type of colorblindness where you lose the cone subtype responsible for GREEN wavelengths

2/3 opsins, missing middle=green wl of light

43
Q

Activation of this alters a membrane current that controls photoreceptor transmitter release

A

Rhodopsin

44
Q

In the absence of light, explain what happens to photoreceptor rhodopsin and its relation to glutamate

A
  1. Rhodopsin is INACTIVE
  2. Na+ channels opens and influx
  3. Cell is DEPOLARIZED
  4. HIGH rate of glutamate is released constantly

cones have the SAME signaling using different opsins.

45
Q

WITH light, explain what happens to photoreceptor rhodopsin and its relation to glutamate

A
  1. Rhodopsin is ACTIVE
  2. Na+ channels CLOSED
  3. Cell is HYPERPOLARIZED
  4. Low rate of glutamate release

basically no glutamate released

cones have the SAME signaling using different opsins.

46
Q

Explain briefly the vertical info flow

A
  1. Rods and cones release glutamate
  2. This is inhibitory or excitatory depending in the glut receptors expressed on the bipolar cell
  3. Bipolar cells release glutamate which is excitatory for ganglion cells

ganglion cells=retinol ganglion cells (RGC)

47
Q

Explain vertical info flow for ON center receptor field (light comes in)

A

Light stimulation causes
1.HYPERPOL of photoreceptor, and no glutamate is released
2. INCR DEPOL of ON center bipolar cell, so mGLU is activated
3. INCR glutamate release from bipolar cells
4. Incr ganglion cell firing rate

48
Q

Explain vertical info flow for OFF center receptor field (light comes in)

A

Light stimulation causes
1. HYPERPOL of photoreceptor, and no glutamate is release
2. DECR DEPOL of OFF center bipolar cell , so NMDA rec is INHIBITED (b/c hyperpol)
3. DECR glutamamte release from off bipolar cells
4. DECR ganglion cell firing rate

49
Q

With light PRESENT is the following cells activated or inhibited?
A. On-center bipolar cell (mGlu)
B. Off-center bipolar cell (NMDA)

A

A. On-center bipolar cell (mGlu): ACTIVATED
B. Off-center bipolar cell (NMDA): INHIBITED

50
Q

With NO light, the following are activated or inhibited?
A. On-center bipolar cell (mGlu)
B. Off-center bipolar cell (NMDA)

A

A. On-center bipolar cell (mGlu): INHIBITED
B. Off-center bipolar cell (NMDA): ACTIVATED

51
Q

What variables contribute to mapping center-surrond receptive field of the retina?

A
  • Duration of spot illumination
  • Size of spot illumination
  • Background light intensitiy of both center and surround area

center compared to peripheral environment

ex:a grey spot next to white looks much darker than the same grey spot next to black

52
Q

What is 20/40 vision?

A

At 20 feet, a human is able to separate line for image recognition that a person with nominal performance can resolve at 40 feet

53
Q

What is 20/20 vision?

A

At 20 feet, a human with normal eye performance is able to separate lines for image recognition

54
Q

What are the 2 types of synaptic transmission in the retina?

A

chemical and electrical

need electrical to identify things moving very quickly

55
Q

What are the two cells involved in lateral information flow and explain their fxn

A
  1. Horizontal cells: release GABA (inhibitory) and form gap junctions.
  2. Amacrine cells: release GABA, glycine, dopamine (inhibitory) and form gap junctions
56
Q

What is lateral inhibition essential for?

A

Essential for identifying shapes (edges) and detecting motion

57
Q

Horizontal cells always have a ____ output via release of ____.

A

inhibitory, GABA

58
Q

What are horizontal cells connected to?

A

Connected laterally to photoreceptor cells, and they suppress vertical information flow in adjacent pathways

59
Q

Explain how horizontal cells play a role in lateral inhibition in this case, for an ON-center receptive field, with NO surround light stimulation

A
  1. There is a dark surround, this inhibits center cone via GABA
  2. Less glutamate release and stimulation of the one-center bipolar cells,
  3. Incr ganglion cell firing
60
Q

Dark stimulated surround ____ center response

A

enhances/incr

61
Q

Explain how horizontal cells play a role in lateral inhibition in this case, for an ON-center receptive field, WITH surround light stimulation

A
  1. Surround photoreceptor is activated and therefore hyperpol with decr release of glut
  2. Reduction of glut reduces release of GABA from horizontal cells
  3. Reduction of gaba inhibition causes dep of photoreceptors in the center and incr release of glut
  4. Incr release of Glu from photoreceptor causes a decr in ON center ganglion cells firing
62
Q

Light stimulated surround ____ center response

A

inhibits/decr

63
Q

Lateral inhibition relies on what?

A

Gap jxns: provides cell-cell coupling

64
Q

What does lateral inhibition promote and amplify?

A

Lateral inhibitions promotes contrast enhancement and amplifies edge detection of the retina

detect edges with shape

65
Q

For information flow to the brain, the visual scene is encoded by the firing patterns of ____ ____, which is further processed in the ____ ____ by the way of the ____ ____.

A

retinal ganglion cells
visual cortex
optic nerve

66
Q

What is the lens retinal prosthesis?

A

A computer chip embedded in lens that mimic retina

67
Q
  1. An MSP3 student arrives late to lecture and decides to sit in the very back row of MDA1209. In order for the lens of his eyes to properly refract light (from the screen) onto the retina, what must occur?

A. Ciliary muscle relaxes; suspensory ligament tightens; lens flattens
B. Ciliary muscle contracts; suspensory ligament relaxes; lens becomes globular
C. Ciliary muscle relaxes; suspensory ligament tightens; lens becomes globular
D. Ciliary muscle contracts; suspensory ligament relaxes; lens flattens

A

A. Ciliary muscle relaxes; suspensory ligament tightens; lens flattens

68
Q
  1. During a bright day on the beach, the rods of your retina become saturated with light and only cones are being used to perceive visual fields. Which of the following best describes this form of vision?

A. Scotopic
B. Mesopic
C. Photopic
D. Lasopic

A

C. Photopic

69
Q
  1. A 24-year-old was recently diagnosed with a form of color blindness known as Deuteranopia due to a genetic malformation of the cones in his retina. Given her condition, which of the following color wavelengths is she not able to perceive?

A. Red
B. Green
C. Blue
D. Yellow

A

B. Green

70
Q
  1. Neuroscientists at the Morsani College of Medicine are studying the effects of light stimulation on retinal neurons and photoreceptors. All of the following are likely to occur during their experiment EXCEPT:

A. Hyperpolarization of photoreceptors
B. Decreased glutamate release from on-center bipolar cells
C. Hyperpolarization of off-center bipolar cells
D. Decreased glutamate release from photoreceptors

A

B. Decreased glutamate release from on-center bipolar cells

71
Q
  1. Horizontal cells play an important role in the modulation of lateral information flow within the retina. More specifically, they are responsible for lateral inhibition. What neurotransmitter do horizontal cells release to execute their function?

A. GABA
B. Glycine
C. Dopamine
D. All of the above

A

A. GABA

Neuroscience Exam 2 (9 decks)

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