Answer
31b. The brain stem contains the neurons of the reticular activating system(RAS). These neurons send a constant stream of impulses to the cerebral cortex that keeps the brain alert and conscious. Injury to the brain stem that impinges negatively on the activity of the RAS neurons will affect the level of consciousness. If the injury is significant enough, a coma , even an irreversible com, may result.
Work Step by Step
The brain stem which comprises the midbrain, the pons and the medulla oblongata also includes the reticular formation --a network of neurons. The reticular activating system (RAS) is a part of the reticular formation. The neurons of the ascending pathways of the RAS send a constant stream of impulses to the cortex that keeps the cortex alert and the mind consciousness. The level of arousal of the cortex decides whether we are fully awake and alert , or inattentive and drowsy. If one's RAS is damaged, one may in turn become stuporous and fall into a com. If the RAS is seriously damaged, an irreversible coma will be the consequence.
Damage to the RAS may be caused by a direct concussive blow to the head; by torsion injury due to twisting of the brainstem in an accident; by compression due to bleeding of the brain, or by brain edema. In any case, if unconsciousness is the result of brain stem injury, it is because the reticular activating system neurons are damaged (or killed) so that they have ceased to transmit enough stimuli to the cortex to support consciousness. This kind of coma is usually irreversible for there is not effective treatment
