Elephant trunk’s ‘stunning’ microscopic musculature may explain its dexterity Etbyerik Stokstad, Science September 26, 2023 See link <https://www.science.org/content/article/elephant-trunk-s-stunning-microscopic-musculature-may-explain-its-dexterity> for graphic. An elephant can lift logs with its trunk and also pick up a potato chip without breaking it. This combination of brute force and soft touch comes from the trunk’s musculature, the most complex known in the animal world. Now, in the most detailed examination ever of this unusual appendage, researchers have mapped and counted the muscle bundles in a baby elephant’s trunk with a special x-ray scanner. The analysis, reported today in Current Biology, suggests elephants get their fine control from almost 90,000 surprisingly tiny bundles of muscle fiber. “This is a highly relevant and exciting scientific paper and discovery,” says Andrew Schulz, a biomechanist at the Max Planck Institute for Intelligent Systems who was not involved. The finding helps explain how the elephant controls its trunk, Schulz notes, and provides insights that may be useful for designing robots with flexible appendages. Like the arm of an octopus, or animal tongues, an elephant’s trunk is one of the few examples of an appendage that can move around without the help of bones. Of those, the elephant’s trunk has the most complicated set of muscles. At a coarse level, eight muscles run on each side of the trunk, plus one that runs the length of the trunk between the nostrils. But the uniqueness of the appendage lies in the fine detail of those muscles. Muscles are made up of sheathed collections of fibers called fascicles. The arrangement of fascicles gives muscles their various functions. Previous studies that dissected trunks ranged widely in their estimates of how many fascicles the appendages have, between 30,000 to 150,000. To get a more accurate tally, researchers led by neuroscientist Michael Brecht of Humboldt University of Berlin used an x-ray-based method known as a computed tomography (CT) scan on the trunk of a 6-day-old baby elephant born in the Leipzig Zoo. The animal broke its leg and couldn’t nurse, so zoo veterinarians had to euthanize it. After receiving the frozen trunk, the researchers sawed it in half lengthwise. The trunk was thawed, stained, and then examined with a CT scanner with much higher resolution than standard devices in hospitals. That was the easy part. Next, the team identified muscle fascicles in four representative parts of the trunk with software, which took about 3000 hours. It was, as Brecht puts it: “Painstaking and sometimes overwhelming, but gratifying in the end.” “This paper is stunningly beautiful and robust anatomical work,” says John Hutchinson, an evolutionary biomechanist at the Royal Veterinary College who was not involved. Extrapolating from the regions studied in depth, the researchers estimate the entire trunk contains more than 89,000 fascicles. The trunk tip, with its “finger” and “lip,” is particularly dense with about 8000 of the tiniest fascicles. At the end of the trunk finger the bundles average just about the diameter of a human hair and, at 2 millimeters long, not much longer than the fascicles in the finger of a mouse. By comparison, the primate hand, one of the most dexterous appendages in nature, has far fewer muscle elements. Fascicles in the human hand are 60 millimeters, 30 times longer than those in the tip of an elephant’s trunk. The team also notes that the trunk’s tip consists solely of fascicles arranged radially, which might be important for the fine control. Hutchinson agrees this makes sense, because radial fascicles can change the tip’s cross sectional profile, allowing it to pucker and poke, for example. The x-ray images show that the main trunk has much larger fascicles than the tip, arranged in two ways. Longitudinal muscles help move the entire trunk up and down, and side to side. Transverse muscles, which spiral around the outside, aid in twisting the trunk. These latter, more radial muscles are present on the top of the trunk, and the more longitudinal muscles on the bottom, which is why the trunk can bend more inward than outward. It’s the big picture that impresses Schulz, who says this new anatomical view will help explain how the trunk manages to flex and elongate when doing its many tricks. (It takes young elephants several years to master them all.) “The trunk is even more complex than we originally thought.” Schulz adds that the pattern of musculature in the trunk has applications for soft robotics. Companies are already making trunk-like manipulators, he points out. Understanding how muscles in various parts of the elephant trunk control its motion could inform better design of mechanical actuators, he says. https://www.science.org/content/article/elephant-trunk-s-stunning-microscopic-musculature-may-explain-its-dexterity https://www.cell.com/current-biology/fulltext/S0960-9822(23)01220-4