Researchers explored the nervous system of octopuses to understand how they coordinate eight arms and hundreds of suckers.
Introduction
Did you know that your ability to move and feel comes from your nervous system? The nervous system helps with communication in an animal’s body. It is made up of cells called neurons. Neurons send messages to each other along nerves. Nerves are like roads that cars use to travel places. But instead of using gas, they use electricity and chemicals. For example, neurons in your brain can send messages through the nerves in your spine to tell your feet to move.
The organization of the nervous system varies in different types of animals. This relates to the shape of the animal. But it also connects to how the animal interacts with its environment. Imagine an octopus. They have eight prehensile arms that are soft and flexible. They also have hundreds of powerful suckers on each arm. They use the suckers to taste, feel, and grab onto objects. Can you imagine the coordination it would take a human to control eight arms at once? Well, the octopus has mastered that coordination!
We know that octopuses have more neurons in their arms than in their brains. But we did not know much about the small-scale organization of the octopus nervous system. We had several questions:
How are the nerves in octopuses organized to help coordinate arm movement?
What about the nerves that reach the suckers?
Is this organization the same for related animals, like squid?
Methods
We studied 17 octopuses from the species Octopus bimaculoides. We also looked at three squids from the species Doryteuthis pealeii, which have eight arms and two tentacles with suckers at the end. We took samples of the animals’ arms. We cut these samples into very thin sections – thinner than a human hair!
We then used colorful stains to see different parts of the nervous system. Each stain sticks to a different protein or structure we wanted to look at. Some stains are like dyes. Other stains are actually made of specific proteins or ribonucleic acid (RNA). These attach to pieces of protein or RNA in the octopus arms. They label specific types of cells, like sensory neurons or motor neurons. When we look at them under a certain type of light, they are fluorescent.
We looked at the central nervous system in each arm, called the axial nerve cord. This is like the spinal cord for each arm. We also looked at the smaller nerves that connect the axial nerve cord to the suckers. We used a special kind of microscope to see both the colorful dyes and fluorescence.
Results
We found strips of neurons separated by gaps in the axial nerve cord (Fig. 1). This means the axial nerve cord is segmented. We saw an average of 7.5 segments for each sucker. We also saw that the axial nerve cord bulges out toward each sucker.
When we looked more closely at the axial nerve cord we found that:
Sensory neurons and motor neurons are not separated. They are in many other animals.
Neurons from neighboring segments can communicate with each other.
The nerves that connect to a sucker all come from the same bulge or enlargement. This gives us a map of the nerves that control the suckers. We call this a “suckerotopy” (Fig. 2).
We found that squid arms with suckers had the same segmented structure as the octopus. We did not see any segments in the parts of the squid tentacles without suckers.
Discussion
Our research shows that the octopus is an incredibly complex animal! We found that the axial nerve cord in each arm is segmented. This is also true for squid arms that have suckers. We think segmentation helps control and coordinate these suckers. Arms without suckers might not need the same level of control.
Suckers are complex. They can “taste” things, feel the environment, and move in lots of directions. It is important for an octopus to be able to control one or a few suckers at a time. The nerve map, or “suckerotopy”, helps explain how they can do this. Let’s say an octopus wants to grab something with one sucker. They can send a signal through the axial nerve cord. The signal then travels through the nerves in the “bulge” to that specific sucker.
In the future, we want to study the nervous system in more animals. Do other animals have the same segmented pattern we found in the octopus? How common is a segmented nervous system? How might a segmented nervous system have evolved? There is lots more to explore!
Conclusion
Nervous systems are complex. They allow animals to sense and respond to their environment in coordinated ways. With eight arms moving independently, an octopus can multitask in a way that humans can only dream about! In fact, there are lots of animals that have skills that easily beat humans. And are super helpful! For example, did you know that reindeer can chew and digest food while they’re sleeping? Why not head to your local zoo or wildlife park (or YouTube!) and discover other cool animal skills you might wish humans had?
