The brain and spinal cord are covered by the meninges, which are three layers or membranes of connective tissue that not only protect the brain and spinal cord, but also form a framework for vessels and venous sinuses. Just think of this as the brain needing three layers of blankets when going to bed at night to make sure it is extra cozy and secure! These three layers, from superficial to deep, are the dura mater, arachnoid mater, and pia mater.

The dura mater is a tough, thick, fibrous external meningeal layer. Deep to the dura mater is the thin arachnoid mater. The dura and arachnoid mater are separated from each other by a potential space called the subdural space. Deep to the arachnoid mater is the pia mater. The pia mater is a delicate vascular layer that is intimately adhered to the brain, covering the gyri and extending along the different sulci and fissures. Together, the arachnoid and pia mater are collectively known as the leptomeninges. Between the arachnoid mater and pia mater is the subarachnoid space, also known as the leptomeningeal space, which is a true space between the arachnoid and pia mater which contains cerebrospinal fluid or CSF for short, as well as major vessels, and cranial nerves.