Nearly one fifth of the blood pumped by the heart is sent to the brain. The brain then sends the blood through an intricate network of blood vessels to where the blood is needed. Specialized blood vessels called choroid plexuses produce a protective cerebrospinal fluid. This fluid is what the brain literally floats in. A third protective measure taken by the brain is called the blood brain barrier. This barrier consists of a network of unique capillaries. These capillaries are filters for harmful chemicals carried by the blood, but do allow oxygen, water and glucose to enter the brain. The area at the front of the brain is the largest. Most of it is known as the cerebrum. It controls all of the movements that you have to think about, thought and memory. The cerebrum is split in two different sections, the right half and the left half. The outer layer of the cerebrum is called the cortex. It is mainly made up of cell bodies of neurons called grey matter. Most of the work the brain does is done in the cortex. It is very wrinkled and has many folds. The wrinkles and folds give the cortex a large surface area, even though it is squeezed up to fit in the skull. The extra surface area gives the cerebrum more area to work. Inside the cortex, the cerebrum is largely made up of white matter. White matter is tissue made only of nerve fibres. The middle region is deep inside the brain. It's chief purpose is to connect the front and the back of the brain together. It acts as a 'switchboard', keeping the parts of your brain in touch with each other. The back area of the brain is divided into three different parts. The pons is a band of nerve fibres which link the back of the brain to the middle. The cerebellum sees to it that all the parts of your body work as a team. It also makes sure you keep your balance. The medulla is low down at the back of your head. It links the brain to the top of the spinal cord. The medulla controls the way your heart pumps blood through your body. It also looks after your breathing and helps you digest food. Nearly one fifth of the blood pumped by the heart is sent to the brain. The brain then sends the blood through an intricate network of blood vessels to where the blood is needed. Specialized blood vessels called choroid plexuses produce a protective cerebrospinal fluid. This fluid is what the brain literally floats in. A third protective measure taken by the brain is called