Shaking or Striking Injuries to the Brain
The exterior of the brain is vulnerable to focal contusions (bruises) from shaking or striking of the head, which bounces the brain against the inner walls of the hard skull. If the contact of brain against skull is hard enough the brain may swell up until it is crushed against the confines of the cranium, which will compress cerebral arteries and cause oxygen deprivation injury (anoxia) similar to stroke, unless the swelling is rapidly reversed by surgery. The interior of the brain is vulnerable to damage from stretching and tearing of axons, known as diffuse shear. Areas of the brain where shearing is particularly likely to occur include the gray matter / white matter boundary and the corpus callosum.
When trauma to the brain causes rupture of blood vessels, an epidural, subdural or subarachnoid hemmorhage will result, depending upon where the vessels break. These bleeds may occur slowly or quickly, and may cause small, medium or large collections of blood, with characteristic shapes, depending on the specifics of the trauma. CT scan is excellent for detecting a bleed. A large bleed will lead to obvious disturbances of consciousness such as blank stare, slurred speech, dilated pupils, lethargy, etc., and will require a craniotomy to remove a clot, or suction the liquid blood.
The inner and outer portions of the brain have different densities. Trauma which rapidly jerks the head around and which exerts rotational force on the brain, makes the inner and outer portions move at different velocities, and this can damage axons at the gray-white matter interface by mechanical stretch.