Medical illustrators and neurological imaging experts have figured out how night-hunting owls can almost fully rotate their heads without damaging the delicate blood vessels in their necks and heads, and without cutting off blood supply to their brains.
Combining angiography, CT scans and medical illustrations to examine the anatomy of a dozen of the big-eyed birds, the Johns Hopkins team, led by medical illustrator Fabian de Kok-Mercado, found four major biological adaptations designed to prevent injury from rotational head movements.
"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," says senior investigator and interventional neuroradiologist Philippe Gailloud, the journal Science reports.
"The carotid and vertebral arteries in the neck of most animals -- including owls and humans -- are very fragile and highly susceptible to even minor tears of the vessel lining," adds Gailloud, associate professor of radiology at the Johns Hopkins University School of Medicine.
Sudden gyrations of the head and neck in humans have been known to stretch and tear blood vessel linings, producing clots that can break off and cause a deadly embolism or stroke, according to a John Hawkins statement.
Researchers say these injuries are commonplace, often resulting from whiplashing car accidents, but also after jarring roller coaster rides and chiropractic manipulations gone awry.
The most striking findings came after researchers injected dye into the owls' arteries, mimicking blood flow, and manually turned the animals' heads.
Blood vessels at the base of the head, just under the jaw bone, kept getting larger and larger, as more of the dye entered, and before the fluid pooled in reservoirs. This contrasted starkly with human anatomical ability, where arteries generally tend to get smaller and smaller, and do not balloon as they branch out.
"Our in-depth study of owl anatomy resolves one of the many interesting neurovascular medical mysteries of how owls have adapted to handle extreme head rotations," says de Kok-Mercado, a scientific illustrator and animator at the Howard Hughes Medical Institute.