This thickening is called the brainstem, and it is divided into three lobes: medulla, pons, and midbrain. The medulla and nuclei (neural clusters) on the floor of the pons control important vital functions like breathing, blood pressure, and body temperature. A hemorrhage from even a tiny artery supplying this region can spell instant death. (Paradoxically, the higher areas of the brain can sustain comparatively massive damage and leave the patient alive and even fit. For example, a large tumor in the frontal lobe might produce barely detectable neurological symptoms.)
