The human brain - Standard format (pdf)
Find out more about The human brain in the full fact sheet.
The brain is the most complex organ in our body and is responsible for everything we do - every thought we have, action we take, memory we have and feeling we experience. This page gives an overview of the brain and someof the main areas within it.
The brain is made up of around 100 billion nerve cells - each one is connected to another 10,000. This means that, in total, we have around a thousand trillion connections in our brains. These are ultimately responsible for who we are. Our brains control the decisions we make, the way we learn, move, and how we feel.
What makes the human brain unique is its size. Our brains have a larger cerebral cortex, or cerebrum than any other animal (see Cerebrum section below). This enables us to have abilities such as complex language, problem solving and self-control.
The brain is protected by the thick bones of our skull and a protective and nourishing fluid called 'cerebrospinal fluid' (CSF). It is separated from the rest of the body's blood stream by the 'blood-brain barrier', which also serves to protect the brain from infection and other substances in the blood.
The cerebrum is the largest part of the brain. It is split in to two 'halves' of roughly equal size called hemispheres. The two hemispheres, the left and right, are joined together by the corpus callosum. The right hemisphere controls the left side of the body and the left hemisphere controls the right side of the body.
The cerebrum is further divided in to four lobes: frontal, parietal, occipital, and temporal, which have different functions. A tumour located in one of the lobes could cause problems relating to the functions carried out by that lobe:
The brain stem connects the cerebrum with the spinal cord. It controls many of the functions we would not usually think about, including breathing, swallowing, blood pressure and digestion. The two main parts of the brain stem are the pons and the medulla oblongata.
The pons takes its meaning from the Latin word meaning 'bridge'. It links together, or acts as a bridge between, different parts of the brain. The pons helps to relay information from the medulla oblongata to higher parts of the brain. Childhood brain tumours in the brain stem usually originate in the pons.
The medulla oblongata carries messages between the brain and the spinal cord. It is partly responsible for heart rate and lung functioning, and controls reflexes such as swallowing, coughing and the gag reflex.
The spinal cord consists of all the nerve fibres that pass down from the brain to the different parts of the body. It is filled with cerebrospinal fluid (CSF), which nourishes and protects it.
The meninges are a thin layer of tissue separating the brain from the skull. They are made of three sheets. Their function is to protect the brain.
The cerebellum, also known as the hindbrain, is the second largest structure of the brain. It sits at the very back of the skull and plays a key role in our balance and co-ordination (which you may hear referred to as 'motor control' functions).
The pituitary gland is a gland of the endocrine system. This means it is a hormone-producing gland. It is often referred to as the 'master' gland as it controls several other hormone-producing glands such as ovaries, testes and adrenals.
It is made up of two main parts, the anterior (front) and the posterior (back), each of which releases hormones targeting different parts of the body. The pituitary gland works with the hypothalamus to control different functions of the body, such as heart rate and body temperature.
This is an area of the brain whose primary function is the control of hormones. This is done by linking the nervous system to the endocrine system via the pituitary gland. Together, the hypothalamus and pituitary gland control the activity of most of the body's other glands. The hypothalamus regulates hormone levels by monitoring their concentration present in the body.
Page last reviewed: 05/2014
Next review due: 05/2017
If you have further questions, need to clarify any of the information on this page, or want to find out more about research and clinical trials, please contact our team:
0808 800 0004 (free from landlines and mobiles)
01252 749 999
Phone lines open Mon-Fri, 09:00-17:00
You can also join our active online community on Facebook - find out more about our groups.