Your brain controls virtually everything you do, feel, think, and experience. It processes information from your senses, stores memories, generates emotions, coordinates movement, and keeps your heart beating and lungs breathing without you ever having to think about it. Despite making up only about 2% of your body weight, the brain consumes roughly 25% of your body’s total oxygen supply, most of which fuels its constant electrical activity.
The Three Major Divisions
The brain has three main parts, each handling different categories of work. The cerebrum is the largest, making up the bulk of what you see when you picture a brain. It handles everything that involves conscious thought: speech, memory, personality, reasoning, judgment, and interpreting what you see, hear, taste, touch, and smell. It’s split into left and right hemispheres connected by a thick bundle of nerve fibers.
The cerebellum is a small, half-circle structure tucked behind the brainstem at the back of your head. It keeps you balanced, maintains your posture, and fine-tunes your movements so you can do things like pick up a cup of coffee without thinking through every muscle contraction. The brainstem sits at the base, connecting everything above it to your spinal cord. It runs the functions you never consciously control: heart rate, breathing, swallowing, and your sleep-wake cycles.
What Each Part of the Cerebrum Does
The cerebrum’s outer surface, the cortex, is divided into four lobes on each side. Each lobe specializes in different tasks, though they all work together constantly.
The frontal lobes, behind your forehead, handle planning, decision-making, and voluntary movement. They also house your working memory, which is your ability to hold and manipulate information you just received, like remembering a phone number long enough to dial it. Parts of the frontal lobes manage social behavior, motivation, and impulse control. On the left side, a specific region controls your ability to produce speech.
The parietal lobes sit behind the frontal lobes and process touch, pressure, temperature, and pain. They also build your sense of where your body is in space, so you can reach for a light switch in a dark room or judge the speed of an approaching car. In most people, the left parietal lobe handles calculation, writing, and left-right orientation, while the right parietal lobe helps you perceive the space around you and do things like draw or read a map.
The temporal lobes, along the sides of your head near your ears, process sound and are essential for understanding language. They also store factual memories and play a central role in emotion.
The occipital lobes, at the very back of your head, are dedicated to vision. They take raw signals from your eyes and turn them into the images you perceive.
How the Brain Keeps Your Body Stable
Deep inside the brain, a structure called the hypothalamus acts as a control center for your body’s internal balance. About the size of an almond, it sits just above the brainstem and manages body temperature, blood pressure, hunger, thirst, mood, sex drive, and sleep. It does this in two ways: by directly controlling your autonomic nervous system (the network that runs automatic body functions) and by managing hormone release through the pituitary gland, which hangs just below it.
The brainstem works in tandem with the hypothalamus, handling the moment-to-moment regulation of breathing rhythm and heart rate. Together, these structures keep your internal environment stable whether you’re asleep, exercising, or sitting in a cold room.
The Brain’s Relay Station
Nearly all sensory information passes through a structure called the thalamus before reaching the cortex. Think of it as a sorting hub. Signals from your eyes, ears, skin, and taste buds arrive at specific zones within the thalamus, which processes them and routes each signal to the correct part of the cortex. Smell is the one exception: it bypasses the thalamus and goes directly to the cortex. Motor signals also pass through the thalamus on their way from planning areas to execution areas, helping coordinate smooth, intentional movement.
Emotion and Memory
Two small structures buried deep in the brain play outsized roles in your emotional life and your ability to form memories. The amygdala, one on each side, processes emotions and assigns value to experiences. It learns associations between things you encounter (a face, a sound, a smell) and whether those things are rewarding or threatening. In humans, this learning can happen extremely quickly, sometimes after a single experience.
The hippocampus, also paired on each side, is essential for forming new episodic memories, the kind that let you recall specific events from your life. It takes in information about where you are, what objects are around you, and what’s happening, then binds those details together into a coherent memory. Later, any part of that memory can trigger recall of the whole event. Over time, memories are gradually transferred to long-term storage areas across the cortex, but the hippocampus is what makes that initial recording possible.
How Brain Cells Communicate
The brain runs on a combination of electrical and chemical signals. Each neuron maintains a slight electrical charge, with the inside of the cell sitting at about negative 70 millivolts compared to the outside. When a neuron receives enough stimulation from other neurons, its charge rises to a tipping point (around negative 50 millivolts), and it fires an electrical pulse called an action potential. That pulse travels down the neuron’s long projection, the axon, until it reaches the end.
At the tip of the axon, the electrical signal triggers the release of chemical messengers called neurotransmitters into a tiny gap, only 20 to 40 nanometers wide, between the sending neuron and the receiving one. Those chemicals cross the gap, attach to receptors on the next cell, and open channels that let charged particles flow in or out. This converts the chemical signal back into an electrical one in the receiving neuron. The entire process, electrical to chemical to electrical, happens in milliseconds and repeats billions of times per second across your brain.
How the Brain Adapts and Rewires
Your brain is not a fixed machine. It physically changes in response to what you do, learn, and experience, a property called neuroplasticity. Early in life, the brain deliberately overproduces connections between neurons. As you grow, a process called synaptic pruning removes the connections you don’t use and strengthens the ones you do. It follows a straightforward “use it or lose it” principle: practice a skill repeatedly, and the neural pathways supporting it become faster and more efficient. Neglect a skill, and those pathways weaken.
This pruning improves learning, memory, and clear thinking by letting your brain concentrate its energy on the pathways that matter most. Neuroplasticity doesn’t stop in childhood. Adult brains continue to form new connections and reorganize existing ones, which is how you can learn a new language at 40 or recover function after a brain injury, though the process is slower than it is in younger brains.
How the Brain Protects Itself
The brain operates in a tightly controlled chemical environment, shielded by a structure called the blood-brain barrier. This barrier is a layer of densely packed cells lining the blood vessels inside the brain. It blocks most bacteria, viruses, and toxic substances from entering brain tissue while holding in the chemicals the brain needs to function properly.
Small, fat-soluble molecules can slip through relatively easily, which is why substances like caffeine, alcohol, and many common pain relievers reach your brain quickly. Larger molecules and water-soluble substances generally cannot pass through on their own. This selectivity is what makes treating brain diseases so challenging: many medications that work elsewhere in the body simply cannot cross the barrier to reach brain tissue.