Human brain explained: parts, lobes and how it controls the body
The human brain has three main parts — cerebrum, cerebellum and brainstem — and four lobes in each hemisphere. Learn what each part does, how neurons carry signals, and why the brainstem is vital for survival.
The human brain is the control centre of the body, built from about 86 billion neurons. Its three main parts are the cerebrum, which handles thinking, memory, speech and voluntary movement; the cerebellum, which coordinates balance and fine movement; and the brainstem, which runs automatic functions such as breathing, heartbeat and blood pressure.
The three main parts
The cerebrum is the largest part of the brain, sitting across the top of the head. It is split into left and right hemispheres, joined by a bundle of nerve fibres called the corpus callosum, and its folded outer layer, the cerebral cortex or grey matter, is where the most complex thinking happens. The left hemisphere largely controls the right side of the body and the right hemisphere the left side.
Below and behind the cerebrum sits the cerebellum, a smaller, half-round structure that fine-tunes movement. It turns rough intentions into smooth, balanced actions, so walking, writing and speaking come out coordinated rather than jerky. Underneath both lies the brainstem, which connects the brain to the spinal cord and keeps the body running without conscious thought.
The four lobes of the cerebrum
Each hemisphere of the cerebrum is divided into four lobes. The frontal lobe, behind the forehead and the largest lobe, controls voluntary movement, planning, judgement, personality and social behaviour. The parietal lobe, near the upper back of the head, interprets touch, temperature and pain and helps you judge where your body is in space.
The temporal lobe, near the ears, processes sound and supports memory, language understanding and emotion. The occipital lobe, at the back of the head, analyses visual information from the eyes; damage here can cause blindness even when the eyes themselves still work.
The brainstem and the inner structures
The brainstem has three sections: the midbrain at the top, the pons below it, and the medulla closest to the spinal cord. The medulla is the most critical for survival, since it regulates heartbeat, breathing and blood pressure even during sleep or unconsciousness, and it sits deep in the head under an extra-thick part of the skull for protection.
Deeper structures handle relay and regulation. The thalamus passes sensory information on to the cortex, the hypothalamus regulates hunger, thirst, body temperature and hormones, and the pituitary gland below it directs hormone activity across the body. The hippocampus supports memory and learning, the amygdala shapes emotional responses such as fear, and the pineal gland helps set sleep and wake cycles.
Neurons, protection and size
The brain's working units are neurons, nerve cells that send and receive electrical and chemical signals, supported by glial cells that nourish them and form myelin, the fatty insulation around nerve fibres. The adult human brain contains close to 86 billion neurons, with roughly as many glial cells, and weighs on average about 3 pounds, growing from about 1 pound at birth.
For protection, the brain floats in cerebrospinal fluid inside the skull, wrapped in three layers of tissue called the meninges: the dura mater outside, the arachnoid membrane in the middle and the pia mater inside. Twelve pairs of cranial nerves carry messages directly between the brain and the head, face and many internal organs. This article gives general educational information only, not personal medical advice.
Editorial disclosure
This article was researched and published with AI assistance. No human prepublication review is claimed. Report factual errors through our contact page.
Frequently asked questions
What are the three main parts of the human brain?
The cerebrum, the cerebellum and the brainstem. The cerebrum handles thinking and voluntary action, the cerebellum coordinates movement and balance, and the brainstem controls automatic functions such as breathing and heartbeat.
Which is the largest part of the brain?
The cerebrum. It is divided into left and right hemispheres joined by the corpus callosum, and its folded outer cortex gives it a large surface area inside the skull.
What are the four lobes of the brain and their functions?
Frontal lobe: voluntary movement, planning, judgement and personality. Parietal lobe: touch, temperature, pain and spatial awareness. Temporal lobe: hearing, memory and language. Occipital lobe: processing visual information.
What does the brainstem control?
Automatic, life-sustaining functions: heartbeat, breathing, blood pressure, swallowing and sleep-wake cycles. Its lowest part, the medulla, keeps these going even during sleep or unconsciousness.
How many neurons are in the human brain?
Close to 86 billion neurons, plus roughly an equal number of glial cells that support, nourish and insulate them.