The brainstem is the lower extension of the brain where it connects to
the spinal cord. Neurological functions located in the brainstem include
those necessary for survival (breathing, digestion, heart rate, blood
pressure) and for arousal (being awake and alert).

Most of the cranial nerves come from the brainstem. The brainstem is
the pathway for all fibre tracts passing up and down from peripheral
nerves and spinal cord to the highest parts of the brain