The brain is the most complicated organ of the human body. The brain is composed of many types of cells, which work together to perform its functions. The brain can be divided into three parts: the brainstem, the cerebellum and the cerebrum. The cerebrum, the largest part, is responsible for the higher functions in the brain such as reasoning, thinking and memory. The cerebellum coordinates movement and balance. The brainstem is responsible for all basic functions in the body such as breathing, heart rate and blood pressure.