Fourth ventricle of the brain, illustration. The ventricles are spaces in the brain, part of the ventricular system that produces and stores the cerebrospinal fluid that cushions the brain and spinal cord. The fourth ventricle (which is diamond-shaped in cross-section) is located within the brainstem. The brain is the nerve centre controlling bodily function and thought. It interprets nerve signals received from the rest of the body and initiates the appropriate responses. The brainstem deals with subconscious functions, such as breathing and blood pressure.