OUR SENSES: WHAT SLUGGISH SLOTHS TELL US ABOUT BALANCE
Published December 1, 2017
[The Museum's logo appears.]
[An illustrated ear, with arms and legs, wobbles on a tightrope.]
[MUSIC PLAYS]
ROB DESALLE (Curator, Division of Invertebrate Zoology):
Balance and hearing are usually associated with each other because the organs that do the sensing of sound waves...
[Ear falls off the tightrope. Tightrope folds up into the shape of sound waves.]
DESALLE: ...and that detect position, they're very close to each other.
[Diagram of the human ear. A sound wave enters the outer ear. In the inner ear, two organs are labeled, "Position (Semicircular canals)," and "Sound (Cochlea)".
DESALLE: They're in the inner ear.
[Curator Rob DeSalle speaks in his office. On-screen text gives his title as "Curator, Division of Invertebrate Zoology."]
DESALLE: They work in somewhat the same fashion, too. The cochlea that detects sound waves...
[An animated soundwave moves behind an illustration of the human cochlea.]
DESALLE: ...has fluid in it, and interacts by...
[Camera zooms into the cochlea, and tiny hairs – represented by pipe cleaners – move back and forth]
DESALLE: ...the hairs being bent by the fluid.
[Illustrated semicircular canals float in a room with graph paper walls. Text identifies them as "SEMICIRCULAR CANALS." An X, Y, and Z appear on the walls, representing the coordinate planes. Arrows pointing in each of the three directions.]
DESALLE: Balance, on the other hand, has three little structures called semicircular canals arranged in an X-Y-Z coordinate fashion.
[Close up of the semicircular canals, as they are filled by animated fluid.]
[FLUID POURING]
DESALLE: These three semicircular canals are filled with fluid, too...
[Hairs, represented by pipe cleaners, pop into the frame.]
DESALLE: ...and are lined with hairs.
[A human silhouette, made from graph paper. The semicircular canals are placed in their approximate position in the head. Arrows indicating the X, Y, and Z-coordinate planes are to the left of the silhouette. The head bends forward.]
DESALLE: And so, if you bend a little bit forward...
[LIQUID SLOSHES]
DESALLE: ...what you're going to do is cause the fluid to go in the Z direction...
[The graph silhouette now has an illustrated brain, and bends upside down.]
DESALLE: ...and that's going to tell your brain, "Oh, I'm bending forward."
[A thought bubble comes out of the head with the text, "Oh, I'm bending forward."]
[An illustrated sloth crawls along a tree branch.]
DESALLE: Sometimes, balance is not that important for animals. Three-toed sloths are awesome because they live in trees...
[Close up of an illustrated sloth's face. The sloth blinks. Slowly.]
[The sloth crawls along a branch. A turtle and a snail race past it.]
DESALLE: ...and they've evolved to be very, very slow.
[A sloth climbs down a tree, holding a roll of toilet paper.]
DESALLE: They rarely come out of the tree except to poop.
[Footage of a sloth crawling awkwardly across the ground.]
DESALLE: And when they do their movements and balance are very, very herky-jerky.
[DeSalle speaks in his office.]
DESALLE: The reason for this is that their semicircular canals have started to degrade.
[Sloth moves slowly along a branch.]
DESALLE: They're a really great example of how a sense is no longer needed and becomes vestigial.
[Wider shot reveals that the sloth is crawling along an illustration of semicircular canals and a cochlea.]
[MUSIC PLAYS]
[Card appears saying: "American Museum of Natural History, Our Senses: An Immersive Experience, Opens November 2017. Our Senses is generously supported by Dana and Virginia Randt."]
[Credits roll.]
We don’t always think of balance as one of our senses, but scientists often consider it as essential as sight, hearing, smell, taste, and touch. For a species like the three-toed sloth, however, there’s little need for this sixth sense.
Check out the Museum’s blog for more info, and visit the exhibition website.