What is brain stem injury?
The functions achieved by the brain of the human newborn are almost entirely in the brainstem. They have to do mostly with basic life processes such as breathing, consciousness, simple movement of the body, the circulation of the blood, heat regulation, the ability to suck, swallow and digest food and the collection and discharge of body wastes. It is when disease or injury affects the brainstem, especially pons and medulla, that life is seriously threatened. The brain stem is also the highway between the cortex and both the internal and external environments. It receives information from the internal environment that there is the need, for example, for rest or water or replenishing energy sources or emptying reservoirs of body wastes, and then the cortex carries out the necessary motor responses.
The external environment has its own almost limitless range of information, both in bits and in highly complex patterns, which the cortex receives and to which it responds in keeping with the needs of the moment. All of these signals must traverse the brainstem. By way of the brainstem the internal environment may also send to the cortex signals of danger-pain, nausea, choking, faintness, shortness of breath, and so on. By way of the brainstem the cortex is able to take the appropriate action. Similarly the cortex, detecting signals of danger in the external environment received by visual, auditory, tactile, smell, or taste sensors and transmitted throughout the brainstem, prepares for appropriate response, including alerting the internal environment of the body to get ready for fight or flight.
Massive brainstem injuries, such as extensive infarctions or barbiturate overdoses, cause coma, but otherwise brainstem injuries do not impair cognition. Also, few illnesses simultaneously damage the brainstem and the cerebrum.
The most frequently observed sign of brainstem dysfunction, which is nonspecific, is nystagmus (repetitive jerk-like eye movements). Other signs of brain injury (coma, irregular breathing, fixation of pupils to light, loss of oculovestibular reflexes, or diffuse motor flaccidity) almost always imply severe injury and a poor prognosis.