um... said:Actually, the sucker works because water can't get drawn in when the radial muscles of the acetabulum are contracted...
Actually, they can't hold onto everything out there The basics of your normal household rubber-suction cup still apply here too, in a limited way though. You see, the texture of the sucker, unlike inflexible rubber, is very yielding and soft, thus I conforms itself to almost any shape much more easily. Still I doubt that an octo would be able to hold onto too rough or even porous surfaces but it still is an amazingly effective mechanism.joel ang said:I've always wondered how octopus suckers could grip on to rough porus surfaces, if you try with suction cups it won't work.
Eh.. huh? :|WhiteKiboko said:i havent followed this thread too closely... if you started enlarging the tentacle system, would there be limit where you start running into diminishing returns?
WhiteKiboko said:non ceph related note, but as i youngester i kept lizards..... ive seen estimates that say if a gecko kept all of its pads on a surface at one time instead of rolling them it could hold several kilos.... dont remember the number but i know it was double digit.... not bad for a lizards weighing a couple of ounces....
6.5 million setae of a single tokay gecko attached maximally could generate 130 kg force [!!!].
WhiteKiboko said:if you started enlarging the tentacle system, would there be limit where you start running into diminishing returns?
Andrew M. Smith said:...small suckers produce greater pressure differentials than large suckers. Suckers larger than 7.5 [square] mm, both decapod and octopod, typically achieve pressure differentials of 100 kPa. As their size decreases below 7.5 [square] mm, octopod suckers get slightly stronger, sometimes producing pressure differentials of 250–300 kPa, while decapod suckers get exponentially stronger, sometimes producing pressure differentials near 800 kPa.
The reason for the greater strength of small suckers is unknown. It is possible that sucker size affects the ability to maintain a seal at the rim. Similar to Laplace’s law for pressurized containers, the stress in the wall of a container holding a reduced pressure may be proportional to the container’s radius. Thus, at a given pressure differential, a smaller sucker may experience lower stresses that might cause the seal at the rim to fail.
pipsquek said:The amazing thing to me about the suckers is that there are so many of them (like 2,240 on a full grown female GPO) and it's all controled by that tiny little brain! And eight arms!
Actually, a lot of the control is from nerve ganglia in the arms near the suckers-- a lot of octopus motor control is distributed around the body, much more so than vertebrates (although vertebrate spinal cords have a fair bit of computational ability, too). Supposedly, severed octopus arms can exhibit a fair amount of behavior, although they can't learn. Also, interestingly, while octopi can learn to distinguish various textures on objects, they can't learn to distinguish between weights of objects. It is (or was, at least) belived that this is because deciding how much force is needed to lift objects is decided locally in the arms, and the result is used for the lifteing but not reported back to the learning center of the brain.
pipsquek said:Non-ceph note- A few months ago I made a elephant (I'm a metal sculptor) to donate for a benefit auction, and I got to go to a ranch that has three rescued elephants. During my private photo shoot, I got fondled by one of them with the trunk. Talk about strong. But the thing I wanted to mention is that the trainer told me that an elephants truck has OVER 100,000 individual muscles, and they are still counting them. At the time I was still working on my GPO as well, and I realized that an elephants trunk and a cephs arms are very similar. Neither of them has any bones, so the only leverage comes from other contracted muscles.
Yeah, Bill Kier, mentioned above, originally studied trunks, tongues, and
tentacles. I think his advisor continues to study trunks and tongues; I can't remember her name off the top of my head, I'm afraid (I'm sure google knows it, though). Trunks, tongues, and cephalopod limbs (and other molusk body parts) are all "muscular hydrostats," which means that they are muscles that can change their relative dimensions, but their volume remains constant, so if they get narrower, they get longer, etc. Kier's work is really interesting and he's a good writer. I recommend it if you're into hanging out at your local university biology library...