The outer part of the brain – the cerebral cortex – is responsible for the brain’s higher functions: consciousness, thinking, and interpreting the senses. The delicate tissue of the cortex is extremely vulnerable, so nature has protected on three levels: physical, chemical, and biological.
It is hard to overstate the importance of protecting the brain from injury. Apart from the obvious immediate damage caused by blows to the head, significant harm can occur, which is not noticeable until much later. Repeated blows to the head, as occurs in boxing, for example, can cause brain damage, and recent research shows that a history of head injury can be a risk factor for Alzheimer’s disease.
Physical protection
The main physical protection of the brain is provided by the cranium, or skull, which consists of several plates of bone joined together. These are typically only a few millimeters thick, but they usually provide sufficient protection against day today knocks and falls.
Some activities require extra physical protection for the brain. Helmets help to minimize the effects of forceful blows to the head, whether the potential risk comes from riding a bicycle or motor cycle, working on a construction site, or engaging in pastimes such as rock – climbing. Most safety helmets today are made of soft polystyrene surrounded by a rigid shell of plastic or fiberglass. A helmet should be replaced immediately after an accident, even if there are no visible signs of damage. Protective helmets should be worn whenever there is a risk of physical injury, but there are limits to the protection they provide. Since the brain is fairly fluid inconsistency, it can easily be damaged by being shaken within the skull, as often happens in road accidents.
Chemical protection
Nature has provided the brain with protection from many poisonous chemicals in the form of the blood-brain barrier. This acts as a filter to keep harmful substances out of the brain and consists of glial cells (which make up the bulk of the brain tissue) wrapped around the tiny blood vessels in the brain. The barrier is so constructed that molecules must effectively pass through two semi-permeable membranes to transfer from the blood to the brain. Useful chemicals – oxygen, carbon dioxide, and most fat-soluble molecules – can readily pass through the blood-brain barrier. Alcohol can also pass through, which is why excessive drinking over many years can damage the brain and lead to psychological problems.
The adult blood-brain barrier is permeable to certain substances that the brain needs for health (such as sodium, potassium, and chloride) but is not permeable to large molecules, such as proteins. The blood-brain barrier in children is less well developed, however, so young brains are more sensitive to certain toxic water-soluble compounds, such as those of mercury and lead. This is why the use of lead – for example, in paint, water pipes, and petrol – has been banned or restricted in many countries.
Biological protection
The brain and spinal cord are surrounded by three protective membrane layers called the meninges, which are bathed in a clear, watery liquid called cerebrospinal fluid.
Delicate structure
The brain sits within the hard, protective covering of the skull. Other mechanisms that serve to shield the brain from damage include the meninges membranes and cerebrospinal fluid.
How to Detect Meningitis
Meningitis is an infection by bacteria or viruses of the meninges membranes surrounding the brain. It is potentially fatal, and early detection is vital. The main symptoms are:
- High temperature
- Severe headache
- Stiff neck
- Photophobia (extreme sensitivity to light)
- Nausea and vomiting
- A blotchy red skin rash that does not fade when a glass tumbler is pressed against it (in bacterial meningitis only).
Anyone suffering from these symptoms – which can occur in any combination and are not always present – should be treated as an emergency, requiring urgent hospital care.
