Which part of the brain governs basic body functions, including respiration and heartbeat?

The brain stem is the part of the brain that governs essential bodily functions such as respiration, heartbeat, and blood pressure regulation. It serves as a critical pathway for messages traveling between the brain and the body, centralizing vital functions that are necessary for survival.

The brain stem consists of structures such as the midbrain, pons, and medulla oblongata. The medulla oblongata, in particular, plays a key role in controlling autonomic functions like breathing and heart rate. This makes it indispensable for maintaining homeostasis in the body.

In contrast, the cerebrum primarily handles higher brain functions, including thought, emotion, and voluntary muscle movements. The cerebellum is involved in coordination and balance, rather than basic life-sustaining functions. The arachnoid is actually a part of the protective membranes (meninges) surrounding the brain and spinal cord, and does not have a role in governing bodily functions. Thus, the most accurate answer for the control of fundamental life functions is the brain stem.