The Brain's Life-Support Core
The hindbrain, evolutionarily the oldest part of the brain, sits at the base of the skull and keeps the body alive moment to moment. The medulla oblongata controls heartbeat, breathing, and other vital autonomic functions — damage here is often fatal. The pons ("bridge") connects the cerebellum to the rest of the brain and helps regulate sleep and arousal. The cerebellum ("little brain"), tucked beneath the cerebral hemispheres, is essential for motor coordination, balance, and procedural (motor) memory; damage produces ataxia — jerky, poorly coordinated movement — even though basic strength and sensation remain intact. Although the cerebellum attaches to the brainstem via the pons, it is not itself classified as part of the brainstem, which consists only of the medulla, pons, and midbrain.
The midbrain, a small relay region above the hindbrain, contains two key structures. The tectum houses the superior colliculus (visual orienting reflexes) and inferior colliculus (auditory orienting reflexes) — together they let you snap your head toward a sudden flash or bang before you consciously register what happened. The tegmentum contains the substantia nigra, a major dopamine-producing region whose degeneration causes the motor symptoms of Parkinson's disease, and forms part of the reticular formation, a network running the length of the brainstem that regulates arousal and consciousness.
Common pitfall: mixing up the superior and inferior colliculus. Superior handles seeing (visual); inferior handles hearing (auditory) — and "superior" comes before "inferior" in that same order alphabetically, if that helps it stick.