The University of Chicago has unveiled new research shedding light on the unique nervous system structure that grants octopus arms their remarkable dexterity. The study reveals that the segmented circuitry within the octopus's nervous system provides precise control over its eight arms and numerous suckers, enabling these creatures to adeptly explore their surroundings, grasp objects, and capture prey.
Clifton Ragsdale, a Professor of Neurobiology at UChicago and senior author of the study, explained: “If you're going to have a nervous system that's controlling such dynamic movement, that's a good way to set it up. We think it’s a feature that specifically evolved in soft-bodied cephalopods with suckers to carry out these worm-like movements.”
Each arm of an octopus contains more neurons than its brain, concentrated in an axial nerve cord. This cord forms enlargements over each sucker as it travels down the arm. Cassady Olson, a graduate student in Computational Neuroscience who led the study, aimed to analyze this structure in the California two-spot octopus (Octopus bimaculoides).
Olson and co-author Grace Schulz discovered through cellular markers and imaging tools that neuronal cell bodies are organized into segments like a corrugated pipe. These segments are separated by septa where nerves and blood vessels exit to muscles. Nerves from multiple segments connect to different muscle regions, indicating collaborative segmental control over movement.
Olson noted: “Thinking about this from a modeling perspective, the best way to set up a control system for this very long, flexible arm would be to divide it into segments. There has to be some sort of communication between the segments which you can imagine would help smooth out the movements.”
The researchers also found that nerves for suckers exit through septa connecting systematically with each sucker's outer edge. This setup creates a spatial map or "suckeroptopy," facilitating complex sensory-motor abilities as octopuses can move their suckers independently.
To determine if similar structures exist in other cephalopods, Olson studied longfin inshore squid (Doryteuthis pealeii). Unlike octopuses, squid tentacle stalks without suckers lack segmentation; however, clubs at their ends do exhibit segmentation akin to octopus arms.
Ragsdale commented on evolutionary implications: “Organisms with these sucker-laden appendages that have worm-like movements need the right kind of nervous system,” adding that different cephalopods have developed segmental structures suited for their environments over millions of years.
This research was published under "Neuronal segmentation in cephalopod arms" by Olson, Schulz and Ragsdale in Nature Communications on January 15th. It received funding from both National Institutes of Health and National Science Foundation.
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