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A guided tour of the brain

The big picture: the brain's main parts, what they do, and how they work together - a plain-language starting point for anyone curious about the brain.

Your brain weighs about 1.4 kg - roughly the size of two fists - yet it runs everything you think, feel, and do. This tour introduces its main parts in plain language. See the brain hub for region cards at a glance.

The three big divisions

Anatomists often split the brain into three broad parts:

  • The cerebrum - the large, wrinkled top part, divided into left and right halves (hemispheres) and four lobes on each side. This is where thinking, sensing, and voluntary movement happen.
  • The cerebellum - the “little brain” tucked at the back and bottom. It fine-tunes movement, balance, and coordination.
  • The brainstem - the stalk that connects the brain to the spinal cord and quietly runs life-support jobs like breathing and heartbeat.

Left and right hemispheres

The cerebrum has two halves joined by a thick bridge of fibres called the corpus callosum. In most people the left hemisphere leans toward language and detail, and the right toward spatial awareness and the “big picture” - but the two constantly talk to each other, and this split is far softer than popular myths suggest. Importantly, each hemisphere controls the opposite side of the body, which is why a stroke on one side affects the other side of the body.

The wrinkles have a purpose

The brain’s folds (gyri) and grooves (sulci) let a large sheet of thinking tissue - the cortex - pack into a small skull. More surface area means more processing power.

Grey matter and white matter

  • Grey matter is the outer layer packed with nerve-cell bodies - the “computers” doing the processing.
  • White matter underneath is the wiring - bundles of fibres (axons) coated in fatty myelin that carry signals quickly between regions.

Always-on housekeeping

Cushioning cerebrospinal fluid floats the brain and clears waste, while a dense network of blood vessels delivers oxygen and glucose. The brain is only ~2% of body weight but uses about 20% of your energy - one reason sleep, food, and blood-flow matter so much for thinking.

Where to go next

Ready to go deeper? Explore each lobe and what changes when it’s affected, or see how the brain’s cells rewire themselves through practice.

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