At each synapse there is a small gap, across which a chemical transmitter passes to take the signal to the next neurone. The human brain looks rather like a huge walnut, with a wrinkled surface split into two halves. An adult brain weighs about 1.5kg and consists of soft grey-coloured material. Its functions are very complex and provide humans with their intelligence and natural curiosity. There are more than one thousand million nerve cells or neurones in the brain, each linked to many others to form a complex network of connections.
Neurones are highly specialized cells.
They depend upon other brain cells, called Schwann cells , for their supply of nutrients. Schwann cells also provide insulation between the neurones so that the signals can transmit correctly. The brain requires a good supply of blood to provide the food and oxygen necessary to maintain its activity. At first sight, all parts of the brain look much the same. However, closer examination shows that it is divided into many distinct areas.