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How Owls Spin Their Heads Without Tearing Arteries

The human neck is a delicate stem. Torque it a bit too much, and the carotid and vertebral arteries can rip, causing deadly strokes. People have torn their neck arteries riding roller coasters, doing yoga, going to the chiropractor, being rear-ended in the car – even leaning back for a beauty-parlor shampoo.

But owls don't have that problem. They can turn their heads 270 degrees, more than twice what a human can safely handle, without any harm. "If a human being was to try to do the same thing, we would dissect our arteries," says Fabian de Kok Mercado.

He wanted to find out why.

Answering that question involved 12 frozen owls and a team of researchers at Johns Hopkins University, where de Kok-Mercado was a graduate student in the Department of Art as Applied to Medicine. Not only did they figure out the secrets of owls' success, de Kok-Mercado's drawings won a first place prize in the National Science Foundation's annual contest for visualizing science.

First, de Kok-Mercado had to round up some owls. Because they're a federally protected species, he worked through nature centers. They happened to have a stash of frozen owls that had been killed by collisions with cars and other traumas.

The Hopkins researchers thawed the owls, and injected radio-opaque dye into their vessels while moving their necks in a scanner to track the flow in real time. That's different than a typical necropsy, which can leave scientists guessing how vessels work in real life.

Owls have a few things going for them that humans don't, it turns out. Their neck arteries don't thread through every vertebra. And where the vessels do go through bone, the canal is much wider than it is in humans. Those two features make it less likely that bone will collide with delicate tissue and injure it.

But that doesn't solve another big problem — having blood flow pinched off, starving the brain. What really surprised the scientists and illustrator is that owls seem to have taken care of, too.

The arteries at the base of the head widen out into reservoirs, unlike typical arteries that narrow the further they go from the heart. The reservoirs make for more blood flow, even if the arteries are pinched elsewhere. And a trigeminal artery connects the front and back of the brain. De Kok-Mercado says: "The blood is going to keep pumping."

In this case, an illustration is worth a lot more than a thousand words, so check out the prize-winning drawings. De Kok-Mercado is now working at the Howard Hughes Medical Institute, where he's bringing other mysteries of science to light. "So much of the science is visual," he says.

And humans are left knowing that lacking that special owl anatomy, we'd be best off not sticking our necks out.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

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