Dura Mater

The dura mater is the outermost layer of the meninges, which cover both the brain and the spinal cord. It is thick and strong, since it is composed of dense connective tissue. This tough layer of the meninges lines closely the inside of the skull as it fuses with the periosteum, which is the dense fibrous membrane that covers the bones. The dura mater lies and extends over the arachnoid, which is the meninges' second layer. There is a very narrow space that stretches between these two layers; it is the subdural space. The dura mater and the arachnoid gets fully separated right after a trauma or inflammation process. When this traumatic event happens, a subdural hematoma is formed; this is the accumulation of clotted blood and fluid in this space.

In some places, the dura mater forms strong infoldings, functioning as anchoring points that serve to restrict the movements of the brain within the skull. Large movements can stretch and damage blood vessels and nerves connecting the brain with the cranium. Thus, from the midline, the dura mater sends a thick overhang or fold between the two cerebral hemispheres; it is called the falx cerebri. Posteriorly, the falx cerebri divides into two parts that extends laterally over the superior surface of the cerebellum, attaching to the temporal pyramid, which is the petrous part of the temporal bone. In the midline, these two parts form the cerebellar tentorium, which is the extension of the dura mater that separates the occipital lobes of both cerebral hemisphere from the superior side of the cerebellum.

The dura mater also extends down into the vertebral canal to enclose the spinal cord. As a matter of fact, it extends further down than the spinal cord, forming a sac around the roots of the lower spinal nerves (cauda equina). This dural sac stretches all the way down to the level of the third sacral vertebra. Thus, below the level of the first and second lumbar vertebrae, the dural sac contains only spinal nerve roots. This the reason it is a safe place to perform a lumbar puncture, that is to enter the subarachnoid space with a needle to take samples of the cerebrospinal fluid (CSF) as there is no danger of harming the spinal cord.

Above, the schematic image shows the three layers of the meninges, with the dura mater lying on top, below the skull.

The dura mater is the thicker and tougher of the three layers of the meninges.