__________ helps in exchange of nutrients between brain and nerve tissues.

Vertebral column - The vertebral column (backbone or spine) is a column consisting of 33 vertebrae. It protects the spinal cord in spinal canal and is not a protective structure of the brain. Meninges are membranes that envelop the central nervous system (brain and spinal cord). The primary function of Meninges is to protect the central nervous system. Aqueous humour is a thick watery substance that fills the space between lens and cornea. Cerebrospinal fluid is a clear body fluid that surrounds the brain. It acts as a cushion for brain and helps in exchange of nutrients between brain and nervous tissues as it flows throughout the inner ventricular system of brain and is absorbed back into the blood stream, rinsing the metabolic wastes from the central nervous system.