The cerebellum is not part of the brainstem, though the answer is more nuanced than a simple no. In standard clinical anatomy, the brainstem consists of three structures: the midbrain, the pons, and the medulla oblongata. The cerebellum is a separate structure that sits directly behind the pons. However, the cerebellum and part of the brainstem share a common developmental origin, which is why some older or more technical classification systems group them together.
What the Brainstem Actually Includes
The brainstem is the stalk-like structure connecting the main bulk of the brain above to the spinal cord below. It has three sections stacked top to bottom: the midbrain at the top, the pons in the middle, and the medulla oblongata at the bottom. These three components handle essential survival functions. The medulla regulates breathing, heart rate, blood pressure, and swallowing. The pons coordinates facial and eye movements, hearing, and balance. The midbrain processes vision and hearing and helps control eye movements.
In virtually every clinical textbook and anatomy reference, this three-part definition is standard. When a doctor refers to the brainstem, they mean the midbrain, pons, and medulla. The cerebellum is not included.
Why the Confusion Exists
The overlap comes from how these structures develop in the embryo. Early in development, the brain forms from a tube that expands into three primary divisions: the forebrain, midbrain, and hindbrain. The hindbrain then splits into two sub-regions. One of those sub-regions gives rise to both the pons and the cerebellum. The other gives rise to the medulla. So developmentally, the cerebellum and the pons are siblings, growing from the same embryonic tissue.
Some neuroanatomy textbooks, particularly when discussing embryology, define the brainstem broadly to include all structures derived from the midbrain and hindbrain, which would technically encompass the cerebellum. This developmental classification is where the “yes” answer comes from. But in practice, when clinicians and most anatomy courses refer to the brainstem, they exclude the cerebellum because it is structurally and functionally distinct.
How They’re Physically Connected
The cerebellum sits behind the pons, forming part of the roof of a fluid-filled space called the fourth ventricle. It attaches to the brainstem through three pairs of thick fiber bundles called cerebellar peduncles. Each pair connects to a different level of the brainstem. The inferior peduncles carry signals primarily to and from the medulla. The middle peduncles receive input from the pons. The superior peduncles send output up through the midbrain.
Both the cerebellum and the brainstem sit together in the posterior cranial fossa, the largest and deepest compartment at the base of the skull. This shared space is one reason the two structures are so often discussed together, and why problems in one can quickly affect the other.
They Do Very Different Jobs
Despite their physical closeness, the cerebellum and brainstem serve fundamentally different roles. The brainstem is a relay highway and control center for basic life-sustaining reflexes. Damage to the brainstem can compromise breathing, consciousness, heart function, and cranial nerve activity. A compressed brainstem can cause a fixed, dilated pupil, paralysis on one side of the body, or in severe cases, coma and death.
The cerebellum, by contrast, is primarily a coordination center. It fine-tunes movements, maintains balance, and helps with motor learning. Damage to the cerebellum produces a very different set of problems: an unsteady, wide-based gait sometimes described as a “drunken sailor” walk, difficulty with precise movements like touching your finger to your nose, tremors that appear only when you’re trying to reach for something, and reduced muscle tone. Cerebellar injuries are disabling but generally not immediately life-threatening the way brainstem damage can be.
This functional split reinforces why anatomy treats them as separate structures. The cerebellum contains more neurons than the rest of the brain combined, packed into its densely folded surface, and operates as a sophisticated processing unit rather than a simple relay station.
The Short Answer
In clinical and standard anatomical usage, the cerebellum is not part of the brainstem. The brainstem is the midbrain, pons, and medulla oblongata. The cerebellum is a neighboring structure that connects to the brainstem and shares a developmental origin with part of it, but it is classified separately because of its distinct structure and function. If you encounter a source that includes the cerebellum in the brainstem, it is likely using a broader embryological definition rather than the conventional anatomical one.