In the central nervous system, there are three different layers that cover the spinal cord and brain. These are called the meninges, which comprise of pia, arachnoid and dura mater. Bone is situated above these layers, followed by periosteum and skin. The dura mater is located at the top, beneath bone tissue. This material at times opens into sinus cavities located around the skull. This is particularly notable with the dural venus sinuses. Here, liquids like blood and cerebrospinal flood drain and collect into the internal jugular vein. Dura mater is also the home to meningeal veins. Many types of medical conditions involve the dura mater. The most common come in the form of hematomas. Due to arterial bleeding, an epidural hematoma results when blood collects between the dura mater at the skull. If blood collects between the dura and arachnoid mater, a subdural hematoma results. Also, there are some instances where the dura plays an active role is some types of headaches.