The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. [1] in the human brain, the brainstem is composed of the midbrain, the pons, and the รขโ‚ฌยฆ The brainstem is a sort of automatic control center for several important involuntary actions of the body, such as heartbeat, breathing, blood pressure, and many reflexes.