Octopus arms display incredible dexterity, bending and twisting with near-infinite freedom. These movements help octopuses explore their environments, manipulate objects, and catch prey.
Recent research reveals a fascinating secret behind this flexibility: segmented nervous system circuitry.
“If you’re going to have a nervous system that’s controlling such dynamic movement, that’s a good way to set it up,” said Dr. Clifton Ragsdale, professor of neurobiology at the University of Chicago.
This segmentation appears to be an evolutionary adaptation specific to soft-bodied cephalopods like octopuses.
Octopus arms are equipped with a remarkably complex nervous system, containing more neurons collectively in their eight arms than in their brain.
This extensive network of neurons is concentrated in a structure called the axial nerve cord (ANC), which runs along the length of each arm.
The ANC is segmented, with each segment corresponding to one of the suckers on the arm. These segments act like local control hubs, with nerves branching out to nearby muscles and sensory structures associated with each sucker.
The segmented organization of the ANC allows the octopus to manage the movement and sensory functions of each sucker independently, enabling precise control over their arms.
This unique design supports the octopus’s extraordinary ability to explore, manipulate, and interact with its environment with unparalleled dexterity.
Graduate students Cassady Olson and Grace Schulz made this discovery while studying the arms of the California two-spot octopus (Octopus bimaculoides).
Using imaging tools, they found that the ANC features columns of neuronal cell bodies separated by gaps, or septa. These septa allow nerves and blood vessels to connect to the muscles and suckers.
“The best way to set up a control system for this very long, flexible arm would be to divide it into segments,” Olson noted.
The study revealed that octopus arms have a “sucker map” in their nervous system – a layout that helps control each sucker with great precision.
This map organizes nerves in a way that allows the octopus to coordinate the movement and sensory input of every sucker individually. Each sucker can move on its own, changing its shape and even functioning as a sensory tool.
When an octopus touches something, it can “taste” and “smell” through receptors in the suckers, much like combining a hand, tongue, and nose into one.
This specialized nervous system design is what enables octopuses to perform complex tasks like manipulating objects, exploring their surroundings, and capturing prey with exceptional dexterity and precision.
The researchers also studied the longfin inshore squid (Doryteuthis pealeii), another type of soft-bodied cephalopod, to compare its nervous system to that of octopuses.
While squid and octopuses share some structural similarities, the study revealed key differences reflecting their unique evolutionary paths.
In squid, the long stalks of their tentacles – used to shoot out and grab prey – do not have segmented nerve structures.
However, the sucker-equipped clubs at the end of these tentacles do show segmentation in their axial nerve cord (ANC), similar to octopus arms.
This suggests that segmentation in the nervous system is specifically adapted to control precise, dexterous movements in appendages with suckers.
The lifestyles of these animals explain the differences. Squid primarily hunt in open water, relying heavily on their vision to locate prey and using their streamlined tentacles to grab it.
In contrast, octopuses explore the ocean floor, using their highly sensitive arms to touch, taste, and manipulate their environment.
These differences highlight how evolution modifies neural designs to meet the unique demands of an animal’s habitat and hunting style.
Each of their eight arms operates almost like a separate brain, packed with its own set of neurons that allow them to perform complex tasks independently.
This means an octopus can explore a crevice with one arm while another is unscrewing a jar or playing with a toy.
Their arms are incredibly flexible and strong, covered in suction cups that can taste, touch, and grip objects with amazing precision.
What’s even more mind-blowing is how octopuses use their arms to solve problems and interact with their environment.
They can manipulate objects, open containers, and even escape from tight spots, showcasing their problem-solving skills and adaptability.
Scientists believe this arm intelligence is one of the reasons octopuses are such skilled hunters and escape artists.
Additionally, their ability to coordinate their arms seamlessly allows them to camouflage themselves by changing color and texture, blending perfectly into their surroundings to avoid predators.
“Organisms with these sucker-laden appendages that have worm-like movements need the right kind of nervous system,” Ragsdale explained.
The segmented ANC in octopuses and squid highlights how evolution optimizes neural designs to meet unique demands.
Despite diverging over 270 million years ago, these cephalopods developed similar neural architectures to control their sucker-laden appendages effectively.
This UChicago research sheds light on how octopuses achieve their unparalleled flexibility and dexterity, offering insights into the intricate relationship between structure, function, and evolution.
The study is published in the journal Nature Communications.
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