Inside the Arm of an Octopus

What am I looking at?

This image is a cross section through the fluorescently stained arm (also known as a tentacle) of a just-hatched octopus. The structures at the top right are bundles of axons (1), which send neural signals up and down the arm. The center structure is a neuropil, which is densely packed with synapses between neurons and serves almost like a secondary brain for processing information within the arm itself (2). The arm’s outer layer, on the edges of the image, is composed mainly of muscle tissue (3).

Biology in the background

Octopuses are considered very intelligent animals. Some researchers believe that their problem-solving skills rival those of humans’ closest evolutionary relatives, chimpanzees. This – combined with their eight muscular arms and a body that can change its shape and color, allowing octopuses to camouflage themselves in almost any setting – makes the octopus a formidable hunter and escape artist.

The octopus has a central brain located right above its beak, at the center of its body. However, the neuropils present at the base of each arm and extending into the arm are so dense with synapses that some scientists have come to believe that octopuses functionally have nine “brains” – one in the center and one in each arm. While the neuropils are not true brains, researchers believe that the neural areas in octopuses’ arms play key roles in helping them detect details of their environment and in coordinating their arm movements.

The neuropil within this octopus arm is about 450 micrometers across, or roughly six times larger than the width of a human hair.

Technique

This image was created using confocal microscopy.