The part of the brain stem that controls autonomic functions.

• A. Pons
• B. Cortex
• C. Midbrain
• D. Medulla

Answer: (D)

Autonomic life-sustaining functions are controlled by centers in the medulla oblongata, a portion of the brain stem. It contains the cardioinhibitory and cardioacceleratory centers that modulate heart rate, the vasomotor center that regulates blood vessel tone and blood pressure, and the respiratory centers that set and adjust breathing rhythm. Parasympathetic output to the heart and viscera is coordinated by nuclei in this region, such as the dorsal motor nucleus of the vagus and the nucleus ambiguus. Breathing rhythm is generated and adjusted mainly by medullary centers, with breathing pattern refined by inputs from the pons. The cortex and midbrain handle higher-order and voluntary functions, not the primary autonomic regulation. So, the medulla is where autonomic control of these vital functions resides.