— Brain Sensitivity & Impacts
Brain sensitivity and impacts
You may imagine the human brain as a gel-like, semi-firm organ. The reality is that it has a similar consistency to a boiled egg white or butter. And because the brain is mostly water, it is incompressible and very weak in shear (unaligned forces pushing the body in two different directions – try putting your hands lightly together, and sliding them apart). All of which makes the brain more sensitive to rotational forces than a purely linear motion of the skull.
What causes the
brain to rotate?
When bike or ski accidents occur, the head is most likely to hit the ground at an angle. At the moment of impact, the tangential force can make the head rotate more or less depending on the impacting object/surface. Unfortunately, standard helmet tests do not mimic reality. Instead, helmets are dropped vertically, resulting in linear motion of the helmet and head.
Impacts from rotational motion
Depending on the severity and site of an impact, the factors and forces that can lead to brain damage are complex. But we do know that where a linear motion of the head can cause a skull fracture or contusion, rotational motion can also cause injuries like concussion, Subdural hematoma or diffuse axonal injury.
Of all the different types of brain injuries, the most common is concussion. But from a simple, albeit painful headache to the extremes of irreparable brain damage, concussion covers a lot of ground. In the US specifically, there are a large number of ongoing research projects trying to understand how repetitive concussions could lead to long-term consequences.