Arachnoid mater; Dura mater; Leptomeninges; Pia mater
Three connective tissue membranes envelope the central nervous system and are collectively known as the meninges. Nearest the nervous tissue, the pia mater is a flat sheet of fibroblasts that follows the sulci and gyri of the brain and spinal cord. The middle layer, the arachnoid mater, is another thin layer of fibroblasts and is separated from the pia by the subarachnoid space. It is within this space that cerebrospinal fluid (CSF) is found. The layer furthest from the nervous tissue is the dura mater and is a much thicker and robust layer. In the skull, the dura contains large blood vessels which can be lacerated in skull fractures causing an epidural hematoma. Trauma can also rupture veins in the arachnoid causing a subdural hematoma with blood accumulating in the potential space between the dura and arachnoid. A subarachnoid hemorrhage results from bleeding into the subarachnoid space due to trauma or an...