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Your brain – what it is and what it does

Photo by National Museums Scotland

The human brain has been described as the most complex object in the universe. It’s responsible for everything you do, think, feel and say – the things that make you who you are and enable you to go about your daily activities.


The brain has three main functions

  1. Unconscious or ‘automatic’ functions, such as heartbeat, breathing, digestion and control of body temperature.
  2. Conscious or ‘motor’ functions, such as movement, gesturing, balance, posture and speech.
  3. Thinking, emotions, behaviour and senses (e.g. sight, sound and touch).

Did you know that the average adult brain is about the size of a medium cauliflower? It accounts for about 2% of total body weight, yet receives 20% of our blood supply and uses 20% of our total calorie intake.


What are thinking skills?

Memory is often the first thinking skill that comes to mind, but there are many more, for example:

  • paying attention to tasks at hand
  • reasoning
  • decision making
  • problem solving
  • planning and organising
  • recognition, e.g. faces, sounds and smells
  • understanding speech
  • vocabulary and language skills
  • learning

Together, our thinking skills give us our identity and sense of self, and enable us to engage with the world around us.

My brain is the most important thing I own and I intend to take care of it.

Lissa, 84 | Coventry

The brain is structured into three main parts

1. The cerebrum

The cerebrum is the largest part of the brain and comprises two halves. The right half controls the left side of the body and the left half controls the right. The outer surface of the cerebrum is known as the ‘cerebral cortex’. It’s highly folded to increase its surface area and is organised on each side into four areas – the frontal, parietal, temporal and occipital lobes. Together, they are responsible for thinking, behaviour, movement, feelings, personality and senses e.g. sight and hearing.

2. The cerebellum

The cerebellum, located above the back of the neck, is responsible for co-ordination and balance.

3. The brain stem

The brain stem is the lower part of the brain that connects to the spinal cord and controls unconscious functions including breathing, heartbeat, digestion and temperature control.


Image provided by Macmillan Cancer Support


How brains work

The brain contains billions of brain cells, called 'neurons.' Each brain cell has a cell body and axons. The cell bodies appear grey-ish in colour, so they’re known as ‘grey matter’. They control all of the brain’s functions.

Axoms and cell bodies
Image provided by Cognitive Ageing and Cognitive Epidemiology (CCACE), University of Edinburgh

Axons radiate out from the cell bodies, forming connections – like wiring – between brain cells. Axons are protected by a fatty sheath called myelin, acting like insulation around an electrical wire. Myelin is white-ish in appearance, so these connections are known as 'white matter'.

Did you know that if you took one second to count each brain cell in a single brain, it would take over 3,000 years to count them all.
[source: National Geographic]

Individual axons come together in bundles to form communication pathways in the brain. These are known as ‘white matter tracts’, illustrated by this image.

White matter
Image provided by the Centre for Cognitive Ageing and Cognitive Epidemiology (CCACE), University of Edinburgh

The brain acts as a highly complex communication system

In the grey matter, the brain cell bodies generate information in the form of electrical signals and the axons carry the signals to other cells. White matter tracts connect different parts of the cerebral cortex and other structures, allowing communication across the brain network.

In this way, information is carried around the brain itself and, via the spinal cord and nervous system, to and from every other part of the body, e.g. muscles, glands and sensory organs (eyes, ears, skin, nose and tongue).

Brain stats

  • The average adult brain contains around 100 billion brain cells.
  • Each is connected to around 1,000 others.
  • That’s 100 trillion connections.
  • There are billions of axons in the brain, but only a handful of primary white matter tracts.

How your thinking skills change with age

With thanks for this page to scientists in the University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology.

For more information call Age UK on 0800 055 6112

Last updated: Oct 10 2017

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