| The human body is a complex structure, composed of billions of cells, organised into organs and tissues which have evolved to carry out specific functions. The human brain, with its 12 billion cells and an almost infinite number of interconnections, may be the most complex structure in existence. Much of the brain is dedicated to co-ordinating the activities of the other organs and tissues within the body and maintaining the optimal environment for the individual cells - a process known as homeostasis. This involves reacting to changes in both the internal and external environment of the body |