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Saturday, February 9, 2013

How the Owls Spin their Head

The 'extreme neck rotation' of a barred owl. (Picture from: http://www.ctvnews.ca/)
Owls do not need eyes in the back of their heads to see what was on the opposite side. Simply by turning the head, eyes facing forward initially be facing backwards. In fact, some species of owls, such as the barred owl, can rotate the head of 270 degrees in every direction. That means they can see to the left by turning the head to the right, or vice versa.

A tawny owl turning its head
far around its neck. (Picture  
from: http://www.livescience.com/)
But how do they do it without injuring the blood vessels or inhibit blood to the brain? A medical illustrator and a physician at Johns Hopkins University School of Medicine in the United States are working together to uncover it.

"Until now, brain imaging specialists like me who deal with human injuries caused by trauma to arteries in the head and neck have always been puzzled as to why rapid, twisting head movements did not leave thousands of owls lying dead on the forest floor from stroke," said Philippe Gailloud, study senior investigator and interventional neuroradiologistone who participated in the research.

If human who tried to turn their heads so fast or far, will torn lining of head arteries and cause the formation of blood clots, which can trigger a stroke. Carotid and vertebral arteries in the neck of most animals, including owls and humans are very fragile and prone to tear slightest vessel lining.

"We found a number of unique traits not previously known," says medical illustrator Fabian de Kok-Mercado, who led this research. The first anatomical variation they discovered was in the owl neck, where one of the major arteries feeding the brain passes through bony holes in the vertebrae. The hollow cavities were approximately 10 times larger in diameter than the vertebral artery traveling through it. The researchers say the extra space in the transverse foraminae, as the holes surrounding the vertebral arteries are known, creates a set of cushioning air pockets that allow the artery to move around when twisted. Twelve of the 14 cervical vertebrae in the owl's neck were found to have this adaptation.
Illustration of an owls 'extreme neck rotation' up to 270 degree. (Picture from: http://io9.com/)
"In humans, the vertebral artery really hugs the hollow cavities in the neck. But this is not the case in owls, whose structures are specially adapted to allow for greater arterial flexibility and movement," says de Kok-Mercado.

In a report published in the journal Science, January 31, 2013, holes or canals that may contain air bags to reduce the twist of the head. "We also saw that the canal was not found in the bottom two vertebrae segments," said De Kok-Mercado. This structure allows the blood vessels to stretch when birds turn heads.
Adaptations of the Owl's Cervical and Cephalic Arteries in relation tio extreme neck rotation. (Picture from: http://blogs.discovermagazine.com/)

Also slightly enlarged vertebral artery near the brain, which is not found in other animals. Enlarged vessels serves as a blood reservoir so that the brain have extra blood when the head rotatesThe team also found that the owl's vertebral artery enters the neck higher up than in other birds - going in at the owl's 12th cervical vertebrae instead of the owl's 14th cervical vertebrae - allowing for more vessel room and slack.

Among de Kok-Mercado and Gailloud's other findings were small vessel connections between the carotid and vertebral arteries - not usually seen in adult humans - that allow blood to be exchanged between the two blood vessels. The researchers say these so-called anastomoses, including a vessel connection called a patent trigeminal artery, allow for uninterrupted blood flow to the brain, even if one route is blocked during extreme neck rotation.

Researchers next plan to examine hawk anatomy to see if other bird species possess the same adaptive features for head rotation. *** [EKA | FROM VARIOUS SOURCES | MNT | LIVESCIENCE | KORAN TEMPO 4134]
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