Have you ever wondered how do octopuses control their tentacles? It’s not a simple challenge. Each of their eight arms is a muscular hydrostat, that is, a soft-bodied structure that lacks a rigid skeleton and moves with almost infinite degrees of freedom.
Not only that, they are also full of hundreds of chemotactile suckers that can change shape independently. But even with that complexity, octopuses effectively control behaviors along a single arm, across all eight arms, and between suckers. How is it possible?
## The octopus nervous system: a wonder of nature
A new research published in Nature asks that question. In the octopus arm, there is embedded a massive nervous system, with more neurons distributed in the eight arms than in the brain.
In the center of each arm, there is a main nervous cord called “axial nerve cord” (ANC). Around this cord, there are other smaller nerves that control the arm muscles and suckers, which are the small “branches” that the octopus uses to grab objects.
Within the ANC, neurons are organized in a layer that surrounds a central zone through which nerve signals pass. This nervous system allows the octopus to control the movement of its arms and suckers independently.
The nerves of the arm are connected to the brain through a nerve tract that goes from the brain to the arms, allowing the octopus to coordinate its movements. That arm nervous system is divided into two areas: one to control arm movement and another to control the suckers.
## Recent discoveries: segmentation and coordination
Although all this is known and how it is organized in general terms, the details of how the nerves work within the arms and suckers are still not understood.
Researchers used advanced techniques to analyze the structure of the axial nerve cord (ANC) in the Octopus bimaculoides octopus. They discovered that the nervous system in the arm is divided into segments, as if they were small blocks.
Each of these segments has groups of nerve cells (neurons) that send signals to nearby areas, and some even connect to opposite parts.
Between these segments, there are barriers (called septa) that do not have many neurons, but they do have nerves, blood vessels, and a substance called collagen, which gives them structure.
The nerves that come out of these barriers have different routes, indicating that the nervous system segments must work together to control the octopus arm muscles.
In addition, the nerves of the suckers, which are in the octopus arms, also pass through these barriers, and by doing so, create a special pattern in each sucker, helping to coordinate its movement.
Researchers compared this with squids and found that both octopuses and squids have a highly organized and segmented nervous system to control their movements.
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