|MadSci Network: Anatomy|
Luckily for us, the brain does not move around a whole lot when you shake your head. The brain is very much like a Jello jiggler that hasn't hardened properly yet. It is protected within the skull by some very touch connective tissue called the meninges. The meninges have three layers, the outer one called the dura mater (Latin for "tough mother"). the dura mater is anchored to the inner layer of the skull. Just under the dura lies the arachnoid membrane, whcih looks like a spider's web (arachnoid comes from the Greek word for spider). Normally there is no space between the dura and arachnoid, but if the blood vessels that pass through the dura mater are torn (as in a skull fracture), blood can collect in the space and form what is called a subdural hematoma. The buildup of fluid in this space can cause a problem with brain function by "squishing" the brain cells. The pia mater ("gentle mother") is a thin layer of cells that lines the surface of the brain. Along the pia run many blood vessels that eventually enter into the brain to supply it with blood. the pia is separated from the arachnoid by a fluid-filled space, the subarachnoid space. This space is filled with salty clear liquid called cerebrospinal fluid, or CSF. Thus in a sense the brain "floats" inside the head in this thin layer of CSF.
So the meninges anchor the brain pretty well. They are assisted a little in this function by blood vessels and nerves leaving and entering the brain. So if you shake your head hard, yes, your brain will move a bit. If your head moves very fast very suddenly (as in a car accident) it is like this mass of Jello slid a bit and hit the wall of the skull. This may bruise it (in other words, some of those blood vessels will rupture leaving a blood clot). As explained earlier, if certain vessels tear, a subdural hematoma could result, or even worse, a subarchnoid hemmorhage. This type of injury may not be known immediately and usually gets worse over time because the brain swells due to the injury (again, "squishing" some of the brain cells - and brain cells, or neurons, don't like being squished). This is especially evident in shaken baby syndrome, because the brain is not as well anchored in place (it's not fully developed yet) the brain is bruised more easily from the baby's head moving back and forth with no support, causing the brain to bruise.
The moral of the story is, though we have a pretty good protective sytem for the brain, don't take it for granted! Always wear a helmet during bike riding, skating, horseback riding, etc. and make sure your friends and siblings do, too. Brains do not heal very well, so you need to protect what you have.
Try the links in the MadSci Library for more information on Anatomy.
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