cephalopod arm proprioception and control

Discussion in 'Physiology and Biology' started by monty, Sep 15, 2007.

  1. monty

    monty Colossal Squid Staff Member Supporter

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    I've been thinking about cephalopod musculature quite a bit recently. Kier has done some great work on the anatomy of musculature in arms and tentacles, and I'm pretty sure there's evidence that the ganglia that run down the arms (usually one per sucker) exert local control over the muscles for each segment (although they're probably not proper segments in that the regions of influence overlap with their neighbors). The autonomy of arms has been well documented, as well as a few papers that show that the arms will sometimes have waves of action go down them like cracking a whip, or will temporarily assign "joints" to bend at and keep the rest rigid. Although there's some local autonomous control, there's obviously some descending control from the brain, too... the arms don't flail around willy-nilly when an octo or squid is swimming, for example.

    But there are several details I'm realizing I don't know at all, though, and one of the biggies is how the nerves control the muscles.

    In vertebrates, one well-studied system in skeletal muscles involves some leg muscles, in particular the one where if the doctor taps your lower knee with a rubber hammer, it elicits a reflex to kick a bit. This is caused by a spinal reflex independent of your brain. In particular, mammal skeletal muscles often have a "set point" for length, so the hammer hit stretches the tendon a bit, and it thinks it has to turn up the muscle force to get the muscle to be the length it's been "set" to by the brain.

    The mechanism for this in vertebrates is rather complicated (and sometimes the "set point" may be a desired velocity or effort level rather than length, or something). But a simplified version is that the brain tells a tiny strand of muscle that has a "stretch receptor" attached to it "try to get to be this length." Then, the tiny muscle pulls on the stretch receptor, and doesn't do squat to actually move the main muscle bundle at all. However, the stretch receptor sends a signal to the spinal cord, saying "I'm a very different length that what the brain asked me to be" which responds to that by sending a signal to the big muscle to pull harder, until it moves the leg to where the stretch receptor isn't stretched any more. This allows the muscles to compensate very quickly for an unexpected force requirement to maintain posture or the like.

    I know that the local ganglia are believed (by Wells) to control the force applied to lift things in octopus as well, he supposes that octos can't learn to discriminate based on weight because the amount of force the arm applies to lift things is decided out in the arm ganglia and never sent back to the learning and memory lobes of the brain. So I imagine that there is proprioception (which is a fancy word for stuff like those stretch receptors that measure body position) in some sort of a tight loop with the ganglia in the arms, but I don't know if the control loop has anything like the "tiny muscle fibers" thing in vertebrates (and I don't even know if that's unique to mammals, or if it applies to birds and lizards and stuff.) I should probably know about cockroaches or crickets, since the central pattern generators for gait control and other neural mechanisms for walking behaviors have been pretty well-studied there, but, well, I don't.

    Does anyone know about this stuff in cephs at all? I'm not sure it's been studied at all... Everyone loves the stellate ganglion, since it's a super-simple escape system that's well-understood, but I can't find much in google scholar about afferents, efferents, proprioception, and the like for motor control in operations that are local to the arms.

    edit: I found this, but don't have time to read it now: http://jn.physiology.org/cgi/reprint/83/3/1315 google scholar is your friend! And I :tentacle: journals that have full-text access without requiring subscriptions!
     
  2. monty

    monty Colossal Squid Staff Member Supporter

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    More arm musculature questions, this time the octopus internal oblique muscles. Kier & Thompson 2003 describe the internal oblique muscles as "perplexing, since it occupies a more central location than the other sets of oblique muscles." There are two cores of oblique muscle near the center of the arms. What neither the text nor the diagrams appear to indicate is whether the fibers slope inwards or outwards as you move along the arm (or one of each) or to get all technical termed, if the muscle fibers go from aboral to oral as one goes from proximal to distal along the arm, or if they go from oral to aboral as you go proximal to distal, or if the ventral internal oblique muscle does one and the dorsal does the other or something like that (assuming dorsal=toward front of octo and ventral=toward back.) Does anyone know the actual orientation of these muscles?

    It also would be great if someone had high-res histology slides of octopus arm muscles stained to show fiber directions. And even better if someone had that histology done in a way that showed the connections of the arms to the brachial crown and on to the head. I'd be happy with any coleoid for this data, by the way.

    I wonder if my old connections with the MRI microscope would let me have a bunch of time to do diffusion tensor MRI on a small octopus...
     
  3. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Monty,
    Would the muscle structure you are studying control the suckers ability to move food to the mouth? I have seen food moving up the arm only once. Mostly I just see arms in the food current and they eventually are not hungry any longer. I see no evidence of collecting the food on the suckers and then moving the arm to the mouth for ingestion. I don't know if the larger octos do as much of it as the Mercs (you have already told me there is no known digestion or absorbsion in the suckers themselves) but there has to be a lot of control for them to filter feed and then move the food to the beak.
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    Most of what I've read is more large scale movements, although there has been some work on how the suckers, well, suck. They do taste stuff, and then supposedly can make local decisions to pass good things to the mouth or bad things away from the mouth, though. I have no idea how they do this sort of stuff with very small things, though.

    I've been looking more at bending, twisting, striking, and so forth, at least so far.
     
  5. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Monty,
    Not that it helps at all with your understanding of arm movement mechanics but there is no question in my mind that the central brain determines the striking and defensive movements (or at least which to use). The Mercs (maybe others) have a rather strange sort of symbiotic relationship with the serpent stars. It appears to be a natural and not learned thing and is interesting to watch. If they are not trying to eat shrimp, they will snap the arm almost whip like to chase them off but when the serpents compete for their food or try to enter their den, the arm movement is very very gentle. All of mine have lifted or moved the serpent arms, regardless on how persistent the serpent is, with firm but very slow and gentle movements.

    I wonder if those stick on magnifiers that they sell for car mirrors would work on the side of a tank to look threw (rather than reflect from behind). BTW, none of my three Mercs have ever investigated the inside of my red tube (the snails have). HideNSeek took up feeding residence under a shell near it for two days but did not venture inside.
     
  6. shipposhack

    shipposhack Haliphron Atlanticus Registered

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    Sorry Monty, this is way over my head. I need a few more years education before I try to read this thread again ^^;. I would have to look up at least (on average) one word per sentence, and that's the LEAST, lol. I don't have that kind of patience or interest right now, but what you're talking about sure sounds cool.

    PS - It seems a lot of the people that would know about this (Steve, Roy, and some others) haven't been online much lately. Maybe they have a secret world-class ceph meeting on a remote island >.>
     
  7. monty

    monty Colossal Squid Staff Member Supporter

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    I'm happy enough to explain what I know about the terminology, if that helps any... Trying to explain it in simple English might be a good exercise to help me understand it, too... I should probably also go look at books and make sure I'm right on some of the terminology, since octos are shaped so differently from the animals that are typically described by medical jargon...

    Of course, some is just names, too... knowing what the words of "internal oblique muscle" mean doesn't really help to know what it is unless you're looking at a picture... I suppose I could include the references, since they're free on the web: http://www.bio.unc.edu/faculty/kier/lab/pdf/Kier_Thompson_2003.pdf is an overview PDF, and figure 7 shows the muscles in an octopus arm (figures 5 and 6 showing squid arms and tentacles are interesting, too.) Most of Kier's papers are here: http://www.bio.unc.edu/faculty/kier/lab/publications.html which is a great resource.

    I usually have to look up words frequently when reading academic papers, too, so don't let it intimidate you... a lot of them sound all fancy, but they're really just shorthand, like "proximal" means "closer to the body" and "distal" means "farther from the body," so that you might say "the wrist is distal to the elbow, and the shoulder is proximal to it."

    Unfortunately, a lot of those terms make sense for animals like humans and cats, where "dorsal" is "on the back" and "ventral" is "on the front," but it's not clear what that means for an octopus. So they invented a few terms like "oral" and "aboral" meaning "on the mouth side" (where the suckers are) and "on the other side from the mouth." There's also "posterior" and "anterior" meaning "back" and "front" but all of posterior/anterior/dorsal/ventral make a lot more sense for humans (dorsal is your back, ventral is your belly, posterior is your butt, and anterior is your head) than they do for octos.

    According to Nixon & Young, if an octo, squid, or cuttle is swimming along horizontally like these

    :vampyro::cuttle:

    then the mantle direction is "posterior," the direction of the arms and tentacles is "anterior," up is "dorsal" (where the eyes are in the octo) and the funnel is "ventral." In nautilus, the tentacles are anterior, and the hood and curl of the shell are "dorsal" (up, when the animal is floating normally.) I seem to remember that in the nautilus embryology page they define the terms differently, though, maybe because for snails it's different, and they wanted to compare them.

    Maybe I should write up some cephalopod anatomy terms and pictures as an article (and have all the real biologists laugh at my mistakes, but help me correct them...)
     
  8. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    Go for it Monty! I thought they would laugh and help me too, but by the time your done with it you might know a little more than them.:goofysca:
     
  9. monty

    monty Colossal Squid Staff Member Supporter

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    Yup, there's no question there is a lot of arm movement controlled at a sophisticated and coordinated level by the brain, I gather that the belief is that the brain does the high-level stuff, but leaves the details up to the local control.

    Something else I wonder about is what the muscles are doing at various times... there seems to be some belief that the whip-type octopus strikes have all the muscles relaxed and send sort of a wave of stiffening up the arm in the direction of the target, but the part ahead of the wave is just left relaxed with all the muscles "floppy." I wonder how often the arms are just relaxed and floppy like that, vs with some muscle tension to provide posture or stiffness... they look to me like they're frequently pretty relaxed, but it's sort of hard to tell, since they often are so graceful that they look relaxed even when they're using their muscles...

    If my :madsci: plans work out, I hope to have a computer animation/simulation of an octo arm where I can specify the controls of the muscles over time, and try various theories like this out and see if they look like actual octo arm movements... but that will require my getting the muscle and body parts working first, then fiddling with how the nervous system might be controlling the arm...

    And then I'll be on my way to building an army of giant, radioactive, cyclopean cephalopod atomic monster mutants with which to conquer the world. But I digress...

    edit: digression aside, I would be very interested in hearing any anecdotes (or seeing any video) all you octo-keepers have about muscle tone, typical and unusual arm motions, and so forth, that might give me some hints on this project. Hints on world conquest should be sent in PMs.
     
  10. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    open PM,
    Try reading (or rereading) The Adolescence of P-1 , Thomas J. Ryan, for thoughts to forward your computer octo-arm conquest.
     
  11. tonmo

    tonmo Titanites Staff Member Webmaster Moderator

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  12. monty

    monty Colossal Squid Staff Member Supporter

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    Yeah, that's a strange one on the placebo effect.

    As long as we're back to this thread, these guys http://www.octopus.huji.ac.il/site/ seem to be on the right track to answering my original questions...
     

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