The human brain has three main parts: the cerebrum, the cerebellum, and the brainstem. But that’s just the top level. Each of those contains smaller structures, and depending on how finely you divide things, the brain can be broken into anywhere from 3 broad regions to 360 distinct cortical areas mapped by modern imaging. The answer depends on the level of detail you’re looking at.
The Three Main Parts
Every description of brain anatomy starts with the same three divisions: the cerebrum, the cerebellum, and the brainstem. These are the structures you can see with the naked eye, and each handles fundamentally different jobs.
The cerebrum is the largest part, making up roughly 80% of the brain’s total weight. It handles everything you think of as “thinking”: speech, memory, reasoning, judgment, personality, and voluntary movement. It also processes your five senses. The cerebrum is split into left and right hemispheres, connected by a bridge of more than 200 million nerve fibers called the corpus callosum, which stretches about 10 centimeters across the middle of your brain. That bridge lets the two sides share information so your senses, movement, and problem-solving all stay coordinated.
The cerebellum sits at the back of the head, below the cerebrum. It’s roughly the size of a fist. Despite its small size, it’s packed with neurons and is essential for balance, posture, coordination, and fine motor skills. Like the cerebrum, the cerebellum has two hemispheres of its own.
The brainstem connects the cerebrum to the spinal cord and controls the automatic functions you never have to think about: heart rate, breathing, sleep-wake cycles, and swallowing.
The Four Lobes of the Cerebrum
The cerebrum’s outer surface, the cortex, is divided into four lobes on each side, giving eight lobes total across both hemispheres. Each lobe is named for the skull bone it sits beneath.
- Frontal lobe: Located behind your forehead. Handles planning, decision-making, personality, voluntary movement, and speech production.
- Parietal lobe: Sits behind the frontal lobe, toward the top of your head. Processes touch, pressure, temperature, and spatial awareness.
- Temporal lobe: Located on the sides of your head, near your ears. Manages hearing, language comprehension, and some aspects of memory.
- Occipital lobe: Found at the very back of the head. Dedicated almost entirely to processing vision.
The cortex itself is covered in ridges and folds that dramatically increase its surface area. Those folds are the reason the brain looks wrinkled.
The Three Parts of the Brainstem
The brainstem breaks down into three smaller sections, stacked on top of each other between the cerebrum and the spinal cord.
The midbrain is the topmost section. It plays a role in motor control, particularly eye movements, and helps process visual and auditory information. Below that, the pons coordinates facial and eye movements, facial sensation, hearing, and balance. The medulla, at the very bottom, controls reflexive actions like sneezing, vomiting, coughing, and swallowing. It also helps regulate heart rate and breathing.
Deep Structures Below the Surface
Beneath the cortex sit several clusters of brain cells that don’t belong to any single lobe but are critical to how you function day to day.
The thalamus acts as a relay station. Nearly all sensory information passes through it before reaching the cortex. Just below it, the hypothalamus regulates thirst, hunger, mood, body temperature, and hormone production. It’s tiny, but it controls much of what keeps your body in balance.
The hippocampus is the brain’s memory center. This is where new episodic memories are formed and organized before being filed away for long-term storage in other parts of the cortex. It also helps with spatial navigation. Nearby, the amygdala drives emotional responses like fear, anxiety, pleasure, and anger. It tags memories with emotional weight, which is why emotionally charged events tend to stick in your memory more than mundane ones. The amygdala is especially important for forming memories related to fear.
Together, these structures (along with others) form what’s loosely called the limbic system, the network responsible for emotional and survival-related behaviors like feeding, reproduction, and fight-or-flight responses.
The Basal Ganglia and Movement Control
The basal ganglia are a group of cell clusters deep inside the cerebrum that act as a filter for movement. When your brain sends a signal to move a muscle, the basal ganglia either approve or reject it. This filtering process is what lets you move one finger without accidentally clenching your whole hand. If the signal gets approved, it travels down through the spinal cord to the target muscle. If not, other brain cells dampen the signal until it fades.
The basal ganglia include several distinct nuclei: the caudate nucleus, the putamen, the globus pallidus, the subthalamic nucleus, and parts of a structure called the substantia nigra. They also receive sensory information from sight, sound, touch, taste, and smell, using that input to refine your movements further. Damage to the basal ganglia is a central feature of Parkinson’s disease, which is why that condition disrupts smooth, voluntary movement.
How Many Regions Has Modern Science Found?
The traditional count of brain “parts” gives you a handful of major structures. But modern brain imaging has revealed a far more detailed picture. In 2016, researchers working on the Human Connectome Project mapped 180 distinct areas in each hemisphere of the cortex, for a total of 360 cortical regions. Of those, 97 per hemisphere were entirely new discoveries, while 83 confirmed areas that had been previously identified. The mapping achieved a nearly 97% detection rate across the individuals studied.
These 360 regions are defined not just by their physical boundaries but by differences in function, connectivity, and cellular architecture. Two neighboring patches of cortex might look identical to the naked eye but respond to completely different tasks and connect to completely different networks.
How Many Cells Make Up the Brain
Regardless of how you divide the brain into regions, the whole system runs on an enormous number of cells. The adult human brain contains roughly 86 billion neurons (the cells that transmit electrical signals) and about 85 billion non-neuronal cells, mostly support cells called glia. The neocortex alone, the wrinkled outer layer of the cerebrum, contains somewhere between 15 and 32 billion neurons depending on the individual. That range means neuron counts can vary by more than a factor of two from person to person.
The support cells break down into several types. The most numerous are oligodendrocytes, which insulate nerve fibers to help signals travel faster. Astrocytes provide structural support and help regulate the chemical environment around neurons. Microglia act as the brain’s immune cells, clearing out damaged cells and debris.
Why the Count Depends on the Question
If someone asks “how many parts does the brain have,” the simplest honest answer is three: cerebrum, cerebellum, brainstem. Go one level deeper and you get the four lobes, the three brainstem segments, the limbic structures, and the basal ganglia, bringing you to roughly a dozen or so named regions. Go to the level of modern brain mapping and the cortex alone has 360 distinct areas, with subcortical structures adding dozens more. During embryonic development, the brain starts as just three simple vesicles (the forebrain, midbrain, and hindbrain) that gradually expand and fold into all the complexity of the adult brain.
The brain isn’t like a machine with a fixed number of parts on a schematic. It’s a continuous structure where boundaries depend on whether you’re looking at anatomy, function, cellular architecture, or connectivity. The “right” number depends entirely on the resolution you need.