Glossary term:


These are membranes which enclose the brain and the spinal cord. There are three, which are very different from one another in nature. The dura is the outermost, lining the inside of the skull and the spinal canal. It is tough and waterproof, retaining the cerebrospinal fluid that bathes the brain and spinal cord. The innermost layer is the pia, which is like a thin skin applied closely to the surface of the brain and spinal cord. Between these two layers is the arachnoid, which is a loose, net-like structure made up of sheets and strands of thin, translucent material, stretching between the dura and the pia. The cerebrospinal fluid flows along the subarachnoid channels, between the arachnoid and the pia.