Our Senses: What Sluggish Sloths Tell Us About Balance

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.]