Why is an injury to the brain stem considered critical

The brain stem which is composed of the Pons, The Medulla, and the Midbrain serve a very vital function... They control the functions that keep you alive; Heart Rate, Respiratory Rate, Breathing input and output, Blood pressure, as well a vasomotor functions. So taking this into account, an injury to the brain stem is extremely bad, as that can and will most definitely be very lethal. 

Answer active artificial immunization;