What is a “deceleration injury” (diffuse axonal injury)?

This sort of injury to the brain occurs when sudden movement of the skull through space (i.e., acceleration) occurs.  When the skull stops moving, for whatever reason (say, for instance, it hits something or is suddenly forced to move in a different direction), then the gelatinous brain inside the hard skull continues to move inside the skull.  When this happens, an injury to the brain occurs.  This is often referred to as “diffuse axonal shearing” because, when the brain is slammed back and forth in the skull, it is compressed and stretched.  The fragile “axons”, which are part of the nerve cells in the brain and spinal cord, are also compressed and stretched.  When this happens, they are injured.  This is called “axonal shearing” and, when this happens, the brain cell dies.