The primary function of the brain stem is to control essential involuntary functions necessary for survival, including breathing, heart rate, and blood pressure regulation. It acts as a vital conduit for signals between the brain and the spinal cord. Additionally, the brain stem plays a role in regulating sleep cycles and reflexes. Damage to this area can be catastrophic, affecting basic life-sustaining functions. The brain stem's importance extends to the integration of sensory information and motor control, making it crucial for overall bodily functions.