Concussion May come as the only result of a head injury, but practically always an accompanying phenomenon of more severe head injuries. Experimental work has demonstrated that sudden acceleration or deceleration of more than 28 ft per second is necessary to produce concussion in cats. Although experimental data suggest that slight morphologic nerve cell changes can be demonstrated, significant structural changes in humans have not been discovered with present techniques. Experiments in cats and monkeys have shown loss of consciousness, loss of autonomic and somatic reflexes, and focal loss of normal histochemical staining reactions in RAS neurons in severe concussion. Clinically, concussion is usually defined as a transient, self-limited disorder in which brain function is abolished, and unassociated with evidence of structural damage.
Amnesia is important in assessing severity of brain injury.
Theories of mechanism of concussion. Other experiments implicate the reticular formation as the major system whose function is abolished in concussion. Sudden death from severe head injury is probably due to extremely severe concussion rather than accompanying contusion or laceration. Usually results from fracture over middle meningeal artery, tearing this vessel. Brain is compressed causing distortion and displacement of midline structures, uncal or cerebellar herniation, and brain stem compression.