THE BRAIN

Brain Anatomy and Problems

The term Central Nervous System (CNS) refers, strictly speaking, to the brain and the spinal cord, though it is commonly extended to include the coverings of those organs (the meninges) and the bony structures which surround them (the skull and spinal column).

The CNS is the very core of our existence. The brain controls our thoughts, emotions, understanding, memory and speech. It interprets and explores our external environment and regulates the functioning of the body as an organism. The spinal cord is the pathway through which information is passed from the brain to the body and back.

Like all living organisms, the CNS is composed of billions of cells of various different kinds. The next section deals with the most important of these cells.

There are two major types of cell in the central nervous system - neurons (nerve cells) and glial cells.

Neurons (of which each of us has about 100 billion) are the cells that do all the clever stuff. By passing electrical signals to each other, they are responsible for every movement we make, every decision we take, every word we speak or emotion we feel.

Glial cells are the backroom boys of the CNS, supporting the neurons. There are several types of glial cells, each with its own specialised function:

• Astrocytes - pass nutrients from the blood vessels to the neurons which consume large quantities of glucose to produce the energy they need. They then carry away the by-products of this digestion back to the blood vessels
• Oligodendrocytes - form the substance called myelin which insulates the axon of a neuron. Myelin is essential for the rapid transmission of electrical impulses.
• Ependymal - cells form the lining of the ventricles of the brain where water (ventricular fluid) is stored.

Before we look at the brain itself, we need to consider where it lives. The brain is such an important and delicate organ that it needs special protection from harm. This is provided by the coverings of the brain.