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Comparative Neurobiology Exam > Invertebrae Vision 1 > Flashcards

Invertebrae Vision 1 Flashcards

1
Q

Steps for Evolutionary Pathways of Opsin Photopigments and Photoreceptor Specializations

A
  1. Evolution of Opsin Photopigments
    • Opsin photopigments evolved, enabling light detection and leading to specialized receptor cells.
  2. Development of Photoreceptor Types
    • Two main types of photoreceptors developed:
      • Ciliary Photoreceptors (CP)
      • Rhabdomeric Photoreceptors (RP)
  3. Evolution of Spatial Vision
    • Spatial vision evolved through both ciliary and rhabdomeric photoreceptors, resulting in two types of eyes:
      • Single-chambered eyes
      • Compound eyes
  4. Single-Chambered Eyes (CP)
    • Evolved from ciliary photoreceptors in:
      • Vertebrates
      • Box jellyfish
  5. Compound Eyes (CP)
    • Evolved from ciliary photoreceptors in:
      • Arc clams
      • Polychaete tubeworms
  6. Single-Chambered Eyes (RP)
    • Evolved from rhabdomeric photoreceptors in:
      • Cephalopods
      • Snails
      • Polychaete lateral eyes
      • Spiders
  7. Compound Eyes (RP)
    • Evolved from rhabdomeric photoreceptors in:
      • Trilobites
      • Xiphosurids
      • Insects
      • Crustaceans
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2
Q

What are the three types of images formed by different eye designs?

A
  • Shadow image
  • refracted image
  • reflected image
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3
Q

What are eye spots in larval trematode worms?

A

Eye spots are the simplest type of eyes found in larval trematode worms.

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4
Q

Describe the characteristics of eye spots = 3

A
  1. Consist of a single photoreceptor.
  2. Shielded by pigment cells.
  3. Provide unidirectional vision but lack spatial information.
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5
Q

What is the significance of spatial vision in the Cambrian Explosion?

A

Spatial vision likely played a crucial role in triggering the Cambrian Explosion, as the evolution of eyes with good spatial vision enabled organisms to perceive their environment more effectively, facilitating the development of diverse body plans and ecological niches.

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6
Q

What are the components of a lens eye?

What organisms possess lens eyes?

A

Lens eyes consist of a lens, which focuses light onto a photosensitive retina, allowing for image formation.

Lens eyes are found in vertebrates, mollusks, and spiders.

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7
Q

What are the components of a compound eye?

What organisms possess compound eyes?

A

– Compound eyes consist of multiple repeating units called ommatidia, each containing a group of retinula cells sensitive to light.

– Compound eyes are found in insects, crustaceans, and polychaete worms.

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8
Q

What is the structure of ommatidia? = 4

A
  1. Crystalline cone: Focuses light onto the rhabdom.
  2. Photoreceptor cells: Found within each ommatidium.
  3. Cell body: Contains the nucleus.
  4. Rhabdomere: Made up of stacks of membrane called microvilli, packed with visual pigment molecules.
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9
Q

What is the function of the crystalline cone in ommatidia?

A

The crystalline cone focuses light onto the rhabdom within each ommatidium.

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10
Q

What is the role of the rhabdomere in ommatidia?

A

The rhabdomere contains visual pigment molecules and is responsible for detecting light stimuli.

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11
Q

What are the advantages of compound eyes? = 5

A
  1. Wide and flexible field of view projected onto a small sheet of receptors.
  2. Large depth of focus, sensitive to movement at any distance.
  3. Short path length of light through the ommatidia reduces loss of UV radiation, allowing for a wide spectral range for vision.
  4. Negligible spherical and chromatic aberration due to short focal length.
  5. Capable of polarisation vision.
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12
Q

What are the disadvantages of compound eyes? = 2

A
  1. Diffraction by small lens facets limits spatial resolution.
  2. Small aperture/lenses limit sensitivity.
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13
Q

How does polarization vision functionally compare to colour vision?

A

Polarization vision functions similarly to colour vision, with visual pigment chromophores preferentially absorbing light polarized parallel to their long axis (Z-axis).

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14
Q
  1. In which organisms is polarization sensitivity (PS) found?
  2. What are the uses of polarization sensitivity (PS)?
  3. Where is PS found in vertebrates?
A
  1. PS is found in many invertebrates, including insects, crustaceans, and cephalopods. It is also found in some vertebrates, such as fish, although the mechanism is unclear.

2.PS serves various purposes, including species recognition, prey detection, and navigation/orientation.

  1. PS is found in some vertebrates, such as fish, but the mechanism is unclear. It may involve structures like the vertebrate rod (ciliary photoreceptor).
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15
Q

How does light interact with matter in the atmosphere?

A

Light undergoes scattering and reflection polarization in the atmosphere.

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16
Q

What determines the pattern of sky light polarization?

A

The position of the sun determines the pattern of sky light polarization.

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17
Q

What is a polarization compass?

A

A polarization compass is a navigational tool that uses the pattern of sky light polarization to determine direction.

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18
Q

How do many insects detect polarization?

A

Many insects have specialized, polarization-sensitive receptors in their eyes, which detect the direction of polarization based on the orientation of microvilli in retinula cells.

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19
Q

What is the significance of eyes in evolution?

A

Eyes have evolved many times in various ways, demonstrating the adaptability of vision across different species.

19
Q

What are compound eyes made of, and why are they abundant?

A

Compound eyes are made from many individual eyelets, and they are the most abundant type of eyes in nature.

20
Q

How do many invertebrates discriminate between differently polarized lights?

A

Many invertebrates can discriminate between differently polarized lights because microvilli, found in their eyes, are inherently polarization-sensitive, functioning similarly to color vision.

21
Q

How do compound eyes and single lens eyes differ in strengths and weaknesses?

A

A: Compound eyes and single lens eyes have different strengths and weaknesses, highlighting the diversity of eye structures and functionalities across species.

22
Q

What trade-off exists in all eyes due to limited space?

A

Light ‘sensitivity’ and ‘spatial resolution’

are traded off in all eyes due to limited space.

23
Q

How do additional functionalities like color vision and polarization vision affect eye effectiveness?

A

Additional functionalities like colour vision and polarization vision can further worsen the trade-off between light sensitivity and spatial resolution.

24
Q

What is the Nyquist limit in terms of eye function?

A

The Nyquist limit states that there should be at least 2 sensors per stimulus cycle
- (1 dark and 1 white bar)
- for effective reconstruction of the viewed grating.

25
Q

What happens if sampling resolution is lower than spatial resolution?

A

Undersampling leads to aliasing, causing distortion in the perceived image.

26
Q

What trade-off exists in eye design due to limited space?

A

Eyes must balance light sensitivity and spatial resolution, and functionalities like color and polarization vision can increase this trade-off.

27
Q

Spatial Resolution 1: Sampling Resolution

Q: How is the inter-ommatidial angle in a compound eye calculated?

A

angle = A/R

where

A is the diameter of the lens and

R is the radius of the eye.

28
Q

How is the acceptance angle in an eye calculated?

A

Angle = d/f

where

d is the diameter of the receptor and

f is the focal length of the lens.

29
Q

What characteristics do eyes with high sampling resolution have?

A

They are large,
- have small lenses (A),
- narrow receptors (d),
- and a long focal length (f).

30
Q

What is a drawback of having small lenses in high-resolution eyes?

A

Small lenses can cause blurring, conflicting with optical resolution.

31
Q

Spatial Resolution 2: Optical Resolution

Q: What does optical resolution measure in an eye?

A

It measures the optical quality of the eye, not the sampling density.

32
Q

What is the Rayleigh criterion in optical resolution?

A

It determines the minimum separable angle (θ), indicating the ability to distinguish two points of light as separate.

33
Q

How do wider apertures (D) affect optical resolution?

A
  • Wider apertures improve optical resolution,
  • allowing for better distinction between two points of light,
  • if the sampling resolution is adequate.
34
Q

What are the two main factors determining spatial resolution in eyes?

A
  1. Sampling Resolution: Determined by the number of receptors, affecting pixelation.
  2. Optical Resolution: Determined by the receptive field size, affecting blurring.
35
Q

What determines the light sensitivity of an eye?

A

The fraction ‘S’ of photons absorbed by the visual pigment in a photoreceptor

36
Q

What is the formula for the fraction ‘S’ of photons absorbed by the visual pigment?

A

S = (pi/4)^2 * (A^2 *(d/f)^2 *kx)/ 2.3+kx
​

37
Q

What do the variables in the light sensitivity formula represent?

A

A: Diameter of the lens

d: Diameter of the receptor

f: Focal length of the lens

x: Length of the receptor (rhabdom)

k: Absorption coefficient

R: Radius of the compound eye

C: Centre of radius of the compound eye

N: Nodal point of the lens in a lens eye

Δρ: Acceptance angle, given by
Δρ= d/f [radian]

38
Q

What are the characteristics of eyes with high light sensitivity?

= 4

A

Eyes with high light sensitivity are:

  1. Large
  2. Have large lenses (A)

3.Have long receptors (x) with a large diameter (d)

  1. Have a short focal length (f)
39
Q

What is the trade-off between resolution and sensitivity in eyes?

A

In all eyes, there is a trade-off between resolution and sensitivity:

  • wider receptors catch more light
  • but reduce resolving power.
40
Q

Give an example of the sensitivity vs resolution trade-off in different species.

= 2

A
  1. Cirolana:
    – Δρ=47° (0.02 cycles/deg)
    – Very sensitive (~4000x more than Callinectes) but low resolution.
  2. Callinectes:
    – Δρ=2° (0.5 cycles/deg)
    – Higher resolution but less sensitive.
41
Q

What are the main concepts that make a good eye? = 4

A
  1. There is a trade-off between light sensitivity and spatial resolution (also applies to colour vision as it requires several types of receptors).
  2. Large eyes are almost always better because they have:
    – 3. Long focal length (low minimum resolvable angle)

– 4. Wide aperture (reduced diffraction and more light capture)

42
Q

What characteristics do eyes with high spatial resolution have? =4

A

Eyes with high spatial resolution are
1. large,

  1. have large lenses (aperture),
  2. narrow receptors,
  3. and a long focal length.
43
Q

What characteristics do sensitive eyes have? = 3

A

Sensitive eyes are large,
1. have large lenses (aperture),

  1. long receptors with large diameter,
  2. and a short focal length.
44
Q

What trade-off exists in eye design due to limited space?

A

Eyes must
1. balance light sensitivity and
2. spatial resolution, and

  1. functionalities like color
  2. and polarization vision can increase this trade-off.

Comparative Neurobiology Exam (2 decks)

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