Octopuses are invertebrate animals, and their brains are quite fascinating. Although they lack a central nervous system like that of birds or mammals, octopuses have multiple neural systems, one for each limb, which allows many to consider each limb to have its own “brain.”
A not-so-central neural system. A research team recently focused on the nervous systems of octopuses to understand how their nine neural organs work together and to what extent they operate independently. The findings, published in Nature Communications, revealed that each of these neural systems can function individually.
Researchers believe that the unique structure of the octopus nervous system enables the animals to achieve remarkable dexterity with their highly flexible limbs. These limbs help octopuses move, feed, sense their surroundings, and even copulate.
“If you’re going to have a nervous system that’s controlling such dynamic movement, that’s a good way to set it up,” study co-author Clifton Ragsdale points out. “We think it’s a feature that specifically evolved in soft-bodied cephalopods with suckers to carry out these worm-like movements,” he says.
Studying segmentation. The recent study focused on segmenting the octopus’ unique neuronal system. The team analyzed the distribution and function of the neurons in the arms of the California two-spot octopus (Octopus bimaculatus). Notably, the total number of neurons in the arms exceeds the number found in the animal’s “central brain,” which is responsible for coordinating actions that require the use of multiple arms.
The limb neurons are concentrated in a large axial nerve cord (ANC) that runs along the arm and connects to each of the octopus’ suckers.
Neural columns. An analysis of the ANC revealed that the neurons in the octopus’ limbs are organized into “columns,” which form segments resembling corrugated pipes. These segments are separated by gaps called “septa,” allowing nerves and blood vessels to reach the muscles of the limb.
“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,” study co-author Cassady Olson explains. “There has to be some sort of communication between the segments, which you can imagine would help smooth out the movements,” she added.
Further research is required. Octopus arms are highly versatile limbs that enable the animals to navigate the seafloor. Additionally, through their suction cups, octopuses can perceive their surroundings, hunt for prey, and feed. Understanding the intricate functioning of these complex limbs will require further research.
Image | Diane Picchiottino
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