The human brain sits within a hard, bony skull. The brain and spinal cord is surrounded by the meninges which enclose and protect the tissue. The meninges consist of three layers, the dura, arachnoid, and pia mater. The dura consists of two layers that are firmly attached to the skull. Below that is the arachnoid, and closest to the brain is the pia. Cerebrospinal fluid (CSF) is in between the space in the meninges and helps cushion the brain.