The human brain is the central organ of the nervous system and controls most body functions. It is protected by three membranes called meninges - the dura mater, arachnoid mater, and pia mater. Cerebrospinal fluid is contained in the brain ventricles and subarachnoid space, where it cushions the brain and nourishes nervous tissue. The brain is divided into the cerebrum, cerebellum, and brainstem. The cerebrum controls thinking and movement, the cerebellum coordinates movement, and the brainstem connects to the spinal cord and regulates basic functions. Blood flows to the brain through arteries that form the circle of Willis.