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How some animals use their heads and avoid concussion

Woodpeckers: a human head butting a tree at woodpecker speed of about 20 times per second would be concussed. But woodpeckers have smaller and lighter brains which experience much less pressure with each peck than we might, thus creating a higher threshold for concussion. It is estimated that a woodpecker would have to hit a tree at twice its normal speed, or peck something four times stiffer than the average tree to get a concussion. It remains to be studied whether woodpeckers have evolved especially small brains for birds of their size, or differently shaped ones (a spherical brain would be better at resisting shocks than an elongated one), and if they also have adaptations that help them cope better with sub-concussive impacts than humans. For example, maybe their brains have little fluid so that they can’t slosh around and get injured; or the fact that their long tongue can wrap around the head and pinch the jugular vein to increase blood volume in the skull creates a protective cushion like bubble wrap, so there’s less room for the brain to move within the cranial cavity.


Musk oxen: male muskoxen settle mating and territorial disputes by ramming into each other

headfirst at high speeds. They are one of the larger ungulates with males weighing up to 900 lbs, and have thick necks and skulls, thick forehead fat pads as well as large curving horns. They charge and collide heads at about 35mph and can do that repeatedly until one of them yields. They can live about 20 years, allowing for a lot of head butting sessions over their lifetime. It is thought that a protective pocket of air between their brain and skull keeps the two from coming into concussive contact, preventing serious damage to the animal’s cerebrum. They are often seen standing looking ‘dazed’ after each head butt for a few seconds, just like you might if you got ‘your bell rung’. But it is unclear if that happens to musk oxen. One study did find some evidence of damage in brains of a few musk oxen, similar to what is seen in chronic traumatic encephalopathy in humans with repetitive head injuries. However it is unclear what that means for the behavior or health of the oxen.


Bighorn sheep: rams butt heads and horns as displays of strength and dominance. Their head butts

sound like huge rocks colliding as the horns smack against each other. Each collision can easily exert enough force to knock out an adult human and cause traumatic brain injury, but the rams

keep it up repeatedly for hours sometimes and walk away without apparent sequelae.

Just how they manage this is not known. They do have thick skull bones that can withstand the crunch of skull-to-skull combat. Their horns are hollow, tapered and spiral curled structures whose geometry is thought to reduce the force from impact. The horns have a bony core and an outer sheath of keratin organized into protein sheets that form hollow, elliptical tubules dispersed in layers. It has been suggested that the horns of bighorn sheep are pneumatic organs filled with air and continuous with the respiratory system, allowing the animal to rebreathe its air to increase carbon dioxide within its blood. Increased CO2 in the blood induces vasodilation and increased intracranial volume creating a tighter fit of the brain inside the cranium and reducing sloshing, and thus, brain injury.


Gannets: these seabirds plunge-dive head first from 100 ft or more at speeds up to 60 mph into a wall of water and somehow avoid brain shattering trauma, presumably due to the design of their heads.

Gannets have a long and narrow beak with a bony plate at the base, long neck with muscles that lock the vertebra into place when diving, a thicker skull built like the nose of a concord jet and air sacs in the face - all of which works to reduce initial impact and distribute the force on the gannet head and body upon entry into water. Studies also show that gannets will roll left or right and change the beak angle before entry into water, perhaps as additional protective behavior. However, the brain anatomy of gannets and impact of the dive forces specifically on the brain have not been studied. It is known that many of the birds live over 20 years and continue to dive over and over without any apparent sequelae to their behavior or health.


Snapping shrimp: they generate supersonic, high-amplitude pressure (shock) waves using their claws. They rapidly clamp their claws when approaching prey, resulting in the creation of popping bubbles accompanied by a snapping sound and shock wave. The shock wave can stun and damage nearby creatures, making them much easier to catch. However, the shrimp themselves are protected from the shock wave impact by an orbital hood that covers the head like a helmet.

The hood has holes that allow water to exit during a shockwave blast, directing the energy away from the shrimp brain and eyes. If scientists remove the hood, there is no apparent issue with normal activity. However, when de-hooded shrimp generate shockwaves to stun nearby prey, their own behavior immediately suggests features of concussive brain injury. They jolt, spin around, and sometimes fall over. Afterward, they move oddly and have difficulty navigating back to their shelter, sometimes appearing to get lost altogether.


Harris 3-spot moth caterpillars: these have found a unique solution to the problem of using your head for impact without sustaining injury. They actually keeps their old discarded head capsules from past moltings and wear them as a tower of hats. If threatened, the caterpillar whips its hat collection back and forth with surprising rapidity using the discarded heads as bludgeons.


Post by: Nadia Fike


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