The Brain
The brain controls all involuntary functions, such as heart rate, breathing and digestion and voluntary functions such as movement as well as performing the more complex functions of thought and reason. It sends and receives messages to and from the rest of the body via the spinal cord and the peripheral nervous system.

The brain and spinal cord are covered by three layers of membrane called meninges and between two of these layers the subarachnoid space which contains cerebrospinal fluid.

The brain itself has three main parts:-

• Cerebrum – this is the largest part of the brain, the forebrain, and is responsible for the higher mental functions such as thought and memory. It has two hemispheres, the left and the right, which although similar to look at have been shown to function slightly differently from one another, the right hemisphere being generally associated with creativity whilst the left is associated with logical abilities.

The two hemispheres of the Cerebrum are further divided into four lobes with each performing a different range of tasks. These four lobes are:-

• Frontal lobe – this is at the front of the brain. It is associated with movement, parts of speech, reasoning and emotions, planning and problem solving
• Parietal lobe – this is at the top and near the back of the head. It is associated with movement, orientation, recognition and awareness of stimuli
• Occipital lobe – this is at the very back of the brain and is responsible for processing visual information
• Temporal lobe – sits at the side of the head, above the ears. It is associated with hearing, memory and speech

• Cerebellum – this is the hind brain, located at the very back of the head and associated with balance and co-ordination. Its activities are automatic so require no conscious control
• Brain Stem – this leads to the spinal cord and controls all the functions that are essential to maintaining life, such as breathing and the heart rate. It is also associated with digestion, blood pressure, and temperature, the reflexes, eye movements and swallowing and provides a sense of balance

Brain Injury
All physical and mental activities are controlled by different parts of the brain but the brain functions as a whole with all the parts interrelating with one another. Traumatic brain injury can cause a loss of cognitive skills such as language and communication, memory, perception and information processing as well as loss of co-ordination, balance, strength and endurance, the ability to walk and fine motor skills. There may also be changes in psychological status.

If the damage is minor it may involve the loss of memory immediately prior to, or immediately after, the accident and some visual disturbance. Sometimes, although the injured person seems to be alright, they may continue to suffer from chronic functional problems and some people will suffer long-term effects where they experience significant changes in personality and thought processes.

One of the most common and devastating forms of traumatic brain injury is diffuse axonal injury which occurs in about half of all severe head injury cases but is also seen in some mild to moderate brain injuries. The damage to the brain is more widespread than in focal brain injury where the injury is as a result of direct impact and deformation of the brain.

Injury can be further categorised as open or closed. Open, also known as penetrating, injuries occur when an object, such as a bullet or shrapnel, enters externally to puncture the skull and leave a track of localised damage in the brain. If the skull is not broken through, the injury is classed as closed.

Road traffic accidents involving cars, motorbikes, bicycles and pedestrians, falls and assaults are the most common causes of traumatic brain injury.