Cushioning Function of the Cerebrospinal Fluid
A major function of the cerebrospinal fluid is to cushion the brain within its solid vault. The brain and the cere-brospinal fluid have about the same specific gravity (only about 4 per cent different), so that the brain simply floats in the fluid. Therefore, a blow to the head, if it is not too intense, moves the entire brain simulta-neously with the skull, causing no one portion of the brain to be momentarily contorted by the blow.
Contrecoup. When a blow to the head is extremely severe, it may not damage the brain on the side of the head where the blow is struck but on the opposite side. This phenomenon is known as “contrecoup,” and the reason for this effect is the following: When the blow is struck, the fluid on the struck side is so incompressible that as the skull moves, the fluid pushes the brain at the same time in unison with the skull. On the side oppo- site to the area that is struck, the sudden movement of the whole skull causes the skull to pull away from the brain momentarily because of the brain’s inertia, creat- ing for a split second a vacuum space in the cranial vault in the area opposite to the blow. Then, when the skull is no longer being accelerated by the blow, the vacuum suddenly collapses and the brain strikes the inner surface of the skull.
The poles and the inferior surfaces of the frontal and temporal lobes, where the brain comes into contact withbony protuberances in the base of the skull, are often the sites of injury and contusions (bruises) after a severe blow to the head, such as that experienced by a boxer. If the contusion occurs on the same side as the impact If the contusion occurs on the same side as the impact the contusion is a contrecoup injury.
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