Controlling octopus motion is a very complex issue. Each of its eight arms is a muscular hydrostat, a soft-bodied structure without a rigid skeleton that moves with nearly infinite degrees of freedom. Additionally, the arm is packed with hundreds of suction cups, each of which can change shape independently. Despite this complexity, octopuses effectively control behavior along the length of a single arm, across all eight arms, and between suckers. In a new study, scientists at the University of Chicago show that the circuits in the nervous system that control the movements of an octopus' arms are subdivided, allowing this extraordinary creature to explore its environment, grasp objects, and capture prey. discovered that he could precisely control his arms and suction cups.
Octopus at USC Wrigley Marine Science Center on Catalina Island. Image credit: University of Southern California.
“If you're going to create a nervous system that controls dynamic movements like this, that's a good way to set it up,” said Clifton Ragsdale, a professor at the University of Chicago.
“We think this is a feature that evolved specifically in soft-bodied cephalopods with suckers for insect-like movements.”
Each arm of an octopus has an extensive nervous system, with more neurons connected across all eight arms than in the animal's brain.
These neurons are concentrated in large axial nerve cords (ANCs) that snake back and forth as they travel along the arm, forming an extension above each sucker with each bend.
The study authors wanted to analyze the structure of the ANC and its connections with the musculature of the arm. California two-spotted octopus (Octopus bimacroides)a small species native to the Pacific Ocean off the coast of California.
They tried to view a thin circular cross-section of the arm under a microscope, but the sample kept falling off the slide.
They tried peeling the arm lengthwise and got lucky, leading to an unexpected discovery.
Using cell markers and imaging tools to track structures and connections from the ANC, they found that neuronal cell bodies are packed into columns that form corrugated pipe-like segments.
These segments are separated by gaps called septa, through which nerves and blood vessels connect to nearby muscles.
Nerves from multiple segments connect to different regions of the muscle, suggesting that these segments work together to control movement.
“If you think about this from a modeling perspective, the best way to set up a control system for this very long, flexible arm is to break it up into segments,” said Cassady Olson, a graduate student at the University of Chicago. states.
“There has to be some communication between the segments. I can imagine that helping smooth the movement.”
The sucker nerves also exit the ANC through these septa and are systematically connected to the outer edge of each sucker.
This indicates that the nervous system sets up a spatial or topographic map of each sucker.
Octopuses can move their suction cups independently and change their shape.
The suckers are also packed with sensory receptors that allow the octopus to taste and smell things it touches. This is the same as combining your hands, tongue, and nose.
The researchers believe that the suckers (what they called maps) facilitate this complex sensorimotor ability.
To see if this kind of structure is common to other soft-bodied cephalopods, the researchers also Long-tailed squid (Dorytheutis Pileyi)common in the Atlantic Ocean.
These squid have eight arms and two tentacles with octopus-like muscles and suckers.
The tentacles have long stalks without suction cups, and at the end are clubs with suction cups.
While hunting, squid can shoot out tentacles and catch prey with clubs equipped with suckers.
Using the same process to study long strips of squid tentacles, we found that the ANC in the suckerless stem was unsegmented, but the club at the end was segmented in the same way as in the octopus. .
This suggests that the segmented ANC was built specifically to control all types of dexterous sucker-equipped appendages in cephalopods.
However, squid tentacle clubs have fewer segments per sucker, probably because they do not use suckers for sensation like octopuses do.
Squids rely on sight to hunt in the open ocean, while octopuses roam the ocean floor and use their sensitive arms as tools for exploration.
Octopuses and squids diverged more than 270 million years ago, but the similarities in how some of their appendages are controlled by suction cups and the differences in others are a question of how evolution always best resolves them. It shows you how to find a solution.
“An organism with insect-like, sucker-containing appendages needs the right kind of nervous system,” Professor Ragsdale says.
“Different cephalopods have come up with segmented structures, the details of which vary depending on environmental demands and hundreds of millions of years of evolutionary pressure.”
of study Published in a magazine nature communications.
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C.S. Olson others. 2025. Neuronal segmentation in the cephalopod arm. Nat Commune 16, 443;doi: 10.1038/s41467-024-55475-5
