Cephalopd eye lecture - PLEASE HELP! :P

Discussion in 'Physiology and Biology' started by lurker, Nov 21, 2008.

  1. lurker

    lurker Pygmy Octopus Registered

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    Hello - I'm preparing all the info I can find about Cephalopod eyes for a Neuphysiology class I'm in. The prof also teaches classes on sensory systems and doesn't know much about Cepholopod eyes, and has offered me extra credit if I bring him up to speed.

    This is the update I sent him yesterday, asking him to ask me questions about the material. I'm sure he'd be more interested in info about the rabdomeres, rhabdomere convergence (what are the collateral axons all about there? Thats pretty similar to the human eye, and ) and is there more specific info about how the Ceph brain processes visual info? I couldn't find much more about the rhabdomere structure being split into 5 subreceptors, either, + that was interesting.

    Thanks

     
  2. lurker

    lurker Pygmy Octopus Registered

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    Oh yeah - I haveta make some powerpoint slides, too, so if anyone has any good images I could use, that'd be appreciated.
     
  3. lurker

    lurker Pygmy Octopus Registered

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    correction: The rhabdomere is not divided into 4. 4 rhabdomeres = 1 rhabdome, and is the functional unit. Also, the rhabdomeres at the center of the retina are longer and thinner than the ones on the periphery, as well as on the equatorial strip. There are many different sizes and shapes of rhabdomeres. The collateral axons forming the aforementioned plexus are efferent, and if they are removed then the rhabdomeres die, leaving the supporting cells (which also have photpigment). If the first layer of the loptic lbe is removed, same result. Removal of any otherlayer yields shorter rhabdomeres. However, the rhabdomeres interdigitate on their proximal ends, so they still talk to each other.
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    Here are some notes for an article I've been putting together on ceph vision; rather scattered and incoherent, I fear, but maybe of some use:

    There's also a good chapter on ceph vision in Complex Worlds from Simpler Nervous Systems, Prete, ed. p.267-307

    Some other good sources are Hanlon & Messenger Cephalopod Behavior, Nixon & Young The Brains and Lives of Cephalopods, and Wells Octopus. I've got a few other xeroxes of related stuff around... the most relevant seems to be from Symposia of the Zoological Society of London #38: The Biology of Cephalopods which has articles on "Pupilary Response of Cephalopods," "Extra-ocular photoreceptors in Cephalopods," and "Optic Glands and the Endocrinology of Reproduction" (since you mentioned being interested in this in another thread.)

    Some other notes:

    photopigments actually move around the receptors to adapt to light levels, so this augments pigmentation.

    extraocular photoreceptors can detect ambient light levels for countershading

    There are theories that the cuttle's W shape leads to two vertical slits intended to make sure that the light coming through the slits hits some specialized areas directly perpendicularly, rather than glancing.

    Sorry this is a bit fragmented, but hopefully it'll help you a bit. Please feel encouraged to post what you find here, if you're willing. I'd love to see a list of your references; I don't think I'd seen the flicker fusion frequency listed anywhere before, for example, so I'm curious where that comes from...

    good luck!
     
  5. lurker

    lurker Pygmy Octopus Registered

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    Its not the quite the same shape. It has a different amino acid sequence.


    Whats the deal with the vampyroteuthis sphincter eye? I looked around a bit, but couldn't find anything about the eye... any links?

    Whatabout the extraocular photoreceptors?
    thanks
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    From what I understand, the functional units of the opsins are fairly well conserved, though. But I didn't mean the shape of the molecule, I meant the shape of its response level graphed against the frequency of the light. And I'd love to have that actual graph, since GPO rhodopsin has been studied extensively, but all the papers I found just say where the peak is, not how wide the response is spectrally.

    http://www.tonmo.com/community/index.php?threads/8199/

    Sorry, no link for that one... just the references I had in the other post. I gotta run shortly, so I don't have time to re-read, but they are used for countershading or estimating the downward light levels in some species, maybe for daily migrations, and possibly for determining other environmental light-level stuff, maybe for seasonal spawning, etc.
     
  7. monty

    monty Colossal Squid Staff Member Supporter

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    Any update on your presentation? I'm working on a ceph vision article for the TONMO articles section, and would be interested in what you found in your research.
     
  8. lurker

    lurker Pygmy Octopus Registered

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    yeah - I turned it in and got enough extra credit to bump my final neurophysiology grade to 100% :p (Never got 100% final grade in anything before, so I'm happy about that!)


    What aspects are you interested in? There is a hot debate on intelligent design regarding ceph eyes vs vertebrate eyes. Seems that the inverted design actually generates too much heat and requires extra vascularization + energy. But ID folks argue the other way around, somehow.

    Cephs eyes make a good model for gradual evolution, and eyes exist pretty much in the whole range from pinhole camera eyes (Nautilus) to the full meal deal, including lens, cornea, fovea, etc. (Octopus) Eyelids come in all shapes + sizes (even sphincters)

    Some ceph lenses are stretched, like vert lenses, but others telescope out like glass lenses do. The refractive gradients are very precise and are established by varying proteins called crystallins (just like vert eyes.) Cephs have some mechanism to constantly maintain the accuracy of this gradient, unlike vertebrates, though.

    Cephalopod light sensors are called rhabdomeres, and are arranged groups of 4 called rhabdomes. This is much like insect eyes. Also like insect eyes, Ceph eyes are designed to see polarized light. They can see vertical and horizontal eyes, but they are confused by diagonal lines. However, they can see every variety of polarized light accurately, even light that is circularly polarized.

    Rhabdomeres send off axons or dentrites (the word I found was 'interdigitate' to each other, like human photoreceptors do. In humans, this works to be a contrast enhancer - photocells mutually inhibit neighbors, so only the ones with the strongest signal power through, and the ones that are 'close but no cigar' get inhibited. They call this signal processing in the eye itself.

    Cuttlefish have a 'W' shaped iris that may present 2 images on each retina, presumably for extra depth perception accuracy.

    The optic lobes of cephs take up about 50% of brain space.

    Cephs brains are shaped as a donut surrounding the esophagus, meaning that they can only eat in small small bites or they'll give themselves a lobotomy. (no cephalopod snakes!)

    lots more, but I can't remember it all. whats your email? I'll send you the powerpoints I made. Any more specific questions?
     
  9. monty

    monty Colossal Squid Staff Member Supporter

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    thanks! And congrats on your 100%!

    monty.mark@gmail.com would be great for the powerpoint slides.

    Most of that is stuff I've got references on, but some of that I didn't know or had forgotten. I'd particularly be interested in references on the retinal "interdigitation" and maybe the lens rigidity vs. flexible bits. References are the ideal thing for me at this stage, since I'm trying to cite sources for everything, but write the article in an accessible style for the "educated layperson," to fit in with the science and fossils articles... I've got a big directory of papers I've downloaded, and a few books, and I'm trying to get it all organized into something coherent.

    Anyway, I'm looking forward to reading your slides... I've been had this on a back burner for over a year, but between your interest and seeing a talk by Roger Hanlon a few weeks ago, I'm trying to get going on it for real (except that I'm going out of town for the holidays, and probably won't bring the big stack of cephalopod books....)
     
  10. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    OK Monty, we have a contest, your completing the eye research and getting the material on-line vs me finishing my Raising O. Mercatoris article. What's the prize?
     
  11. gholland

    gholland Haliphron Atlanticus Supporter

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    Oh really... how's that article coming along D? :lol:
     
  12. monty

    monty Colossal Squid Staff Member Supporter

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    the honor and respect of the masses?
     
  13. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    I have an outline, reread my original journal (I hope I write better than that now, or at least don't give octopuses tentacles) and an intro paragraph exposing my limited experience. Are you volunteering to be co-author?:sagrin:

    You mean we don't already have that? :roll:
     
  14. gholland

    gholland Haliphron Atlanticus Supporter

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    Doh! Co-author would be a just punishment since I also called them tentacles once upon a time! Actually, I'd be happy to assist in whatever way I can.... but you'd better get my time now before the spring semester starts up! :bonk:
     

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