Final answer:
The hypothalamus is the brain structure responsible for controlling sympathetic and parasympathetic activation in the autonomic nervous system.
Step-by-step explanation:
The brain structure responsible for controlling sympathetic and parasympathetic activation in the autonomic nervous system is the hypothalamus. It is considered the master control center for homeostasis through the autonomic and endocrine systems. The hypothalamus regulates activities of the organ systems of the body by coordinating sympathetic and parasympathetic pathways.