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Organ Systems III MTI Neuroanatomy > Visual System Part II: The Retina > Flashcards

Visual System Part II: The Retina Flashcards

1
Q

Where is the fovea centralis? What does it contain and what is its function?

A

Central point of retina with only cones and no rods. High levels of visual acuity.

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2
Q

Contains axons of “ganglion cells” but no receptor cells

A

Optic disc “Blind spot”

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3
Q

What is the macula lutea? What gives it its color? What is one of its functions?

A

Yellow area surrounding fovea.
Color = lutein and zeaxanthin (carotenoids)
Both pigments are antioxidants and absorb excess blue and UV light (protective)

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4
Q

What does the central artery of retina do? Describe its path.

A

Blood supply to retina.
Branch of internal carotid a.
Thru optic tract and exits onto inner surface of retina between retina and vit. humor.

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5
Q 
Order these retinal layers from outer to inner eye.
Photoreceptors (rods and cones)
Ganglion cells
Retinal pigmented epithelium
Neural cells (bipolar, horizontal)
A 
Outer --
Retinal pigmented epithelium
Photoreceptors (rods and cones)
Neural cells (bipolar, horizontal)
Ganglion cells
Inner --
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6
Q

Describe structure of rods and cones, including pigments and transmitters.

A

Outer segment w/ stacks of vesicular discs containing pigments.
Iodopsin - cones
Rhodopsin -rods
Inner segment w/ nucleus and synaptic terminal that releases glutamate

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7
Q

Part of visible light spectrum that rod and cone pigments respond to?

A

450-700 nm

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8
Q

How to photoreceptors respond to light?

A

Hyperpolarize and release less glutamate

  1. Light converts 11-cis-retinal to trans-retinal.
  2. Causes opsin to activate PDE via transducin (G protein)
  3. PDE reduces cGMP –> closes Na+ and Ca+ channels
  4. Hyperpolarizes cell
  5. Less glutamate released.
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9
Q

Rod or Cone?

Photopic - vision in bright light

A

Cones

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10
Q 
Rod or Cone?
High sensitivity (more pigment, night vision)
A

Rods

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11
Q

Rod or Cone?

Low acuity, not present in fovea

A

Rods

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12
Q

Rod or Cone?

Sensitive to direct axial sunlight

A

Cones

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13
Q

Rod or Cone?

Good spatial resolution

A

Cones

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14
Q

Rod or Cone?

Chromatic - three types of pigmented cells respond to different parts of the spectrum

A

Cones

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15
Q

Does peripheral vision have color?

A

Yes. Thin layer of cone cells evenly distributed on rest of retina

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16
Q

What features of the fovea allow it to have the highest possible level of visual acuity?

A
  1. Only cones - favor acuity and color
  2. Cones more exposed to light by outward dispersal of ganglion and other integrative cells
  3. Each cone activates single ganglion
17
Q

T or F?

Choroid is behind retina so that light reception is not affected by ganglion and bipolar cells.

A

False. Light reception not affected by b.v.s in choroid.

18
Q

T or F?

Inner layer retinal cells get nutrients from smaller retinal arteries

A

True

19
Q

T or F?

Pigment turnover in photoreceptors requires high O2 levels so RPE close to choroid (blood supply).

A

True

20
Q

T or F?

Light is refracted by ganglion and bipolar cells.

A

False. Light passes thru ganglion and bipolar cells w/o distortion b/c they have same refractive index as vit humor.

21
Q

What are the functions of the RPE?

A
  1. Visual acuity (limit reflection of light back to PRs)
  2. Antioxidant (needed b/c absorp. of blue light increases ROS)
  3. Maintain photoreceptor excitability (trans-retinal is reformed into cis-11-retinal)
  4. Nutrient (transports glucose and retinal to PRs)
  5. Phagocytosis of photoreceptor cell debris from light reception
22
Q

What is retinitis pigmentosa?

A

Deficient uptake of membrane fragments (metabolic debris), which accumulate and separate the receptors from the choroid, leading to anoxia and cell death

23
Q

Why is the fovea avascular?

A

Reduces vascular interference with high acuity.

24
Q

How does the fovea receive nutrients? Get rid of waste?

A

Capillaries encircle fovea to supply it.
No veins. Extravasated salt & water is transported from the extracellular space into the choroid veins via membrane transporters in the RPE.

25
Q

How does retinal detachment occur?

A

The contact bet. neural retina and RPE is mechanically unstable. In detached retina, neural retina tears away from RPE.
Macular degeneration can detach the retina.

26
Q

How is vision affected by macular degeneration?

A

Blindness in fovea/center

27
Q

What is the difference between “wet” and “dry” macular degeneration? Which one is also called exudative? Which one is more serious?

A 
Wet = Abrupt lesion of b.v. that separates RPE and receptor cells (exudative, more serious)
Dry = Slow build up of metabolic waste separates choroid from receptor cells and interferes with nutrient supply to receptor cells.
28
Q

What is the role of bipolar, horizontal, and amacrine cells?

A

Integrate information from receptor cells and activate ganglion cells

29
Q

What is the role of ganglion cells?

A

Output of retina. Transmit visual information to thalamus, superior colliculus, and other brain stem areas.

30
Q

Where do ganglion cells converge?

A

Converge at optic disc to form optic nerve

31
Q

The optic nerve/tract consists of …

A
  1. axons of ganglion cells
  2. CNS ganglia
  3. central artery and veins of retina
32
Q

What cells make up the CNS glia and what do they do?

A

Oligodendricytes myelinate the axons

Astrocytes surround cell bodies and dendrites; contact blood vessels

33
Q

What is papilledema?

A

Increased CSF pressure limits venous return from retina

Pressure extends around optic nerve and causes edema (bulge) under optic disc

34
Q

What would you see through an opthalmoscope in a person with papilledema?

A

Blurred margins of optic disc.

Dilated tortuous veins

35
Q

What are two symptoms of papilledema that you would not be able to see through an opthalmoscope?

A

Expanded CSF space around optic nerve.

Axoplasmic stasis of ganglion cells

36
Q

Would you see increased, decreased, or normal intraocular pressure in papilledema?

A

Normal

37
Q

Why is the optic disc called the “blind spot”

A

No receptor cells, no cells to respond to light.

38
Q

Why don’t we have a blank circle in our vision due to the blind spot?

A

Interpolation via saccadic eye movements or by activity in visual cerebral cortex.

Organ Systems III MTI Neuroanatomy (5 decks)

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