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 journals that have full-text access without requiring subscriptions!