The dura mater is the outermost and most robust of the three protective layers, known collectively as the meninges, that surround the central nervous system. This dense, fibrous membrane acts as a protective barrier, encasing both the brain and the spinal cord. Its primary function is to shield the delicate neural tissue from external mechanical forces and provide a stable internal environment. The dura mater is positioned directly beneath the bony structures of the skull and vertebral column.
Structure and Position of the Dura Mater
The dura mater in the skull is composed of two distinct sheets of connective tissue that are largely fused together. The outer layer is called the periosteal layer, which adheres tightly to the inner surface of the skull bones, functioning as the internal periosteum of the cranium. This layer does not continue down the spinal cord, remaining confined to the skull cavity.
The inner layer is the meningeal layer, a dense, fibrous membrane that covers the brain tissue and is continuous with the dura mater surrounding the spinal cord. These two dural layers are fused in most areas, giving the dura its characteristic thickness and strength. They separate only in specific locations to create channels critical for the brain’s circulation.
The Dura’s Role in Brain Stability and Circulation
Beyond protection, the dura mater stabilizes the brain’s structure and manages its fluid circulation. The inner meningeal layer folds inward in several places to form partitions, known as dural reflections or septa, which divide the cranial cavity into compartments. These folds act as internal seatbelts, anchoring the brain and limiting its movement within the skull during sudden acceleration or deceleration.
The largest of these folds is the falx cerebri, a sickle-shaped partition that separates the right and left cerebral hemispheres. Another significant fold is the tentorium cerebelli, which forms a tent-like roof over the posterior cranial fossa, separating the cerebrum above from the cerebellum below. These dural reflections prevent different parts of the brain from colliding with each other or with the skull bone during rapid head movements.
The separation of the two dural layers creates large, low-pressure channels known as dural venous sinuses. These sinuses collect deoxygenated blood from the cerebral veins. They also receive cerebrospinal fluid (CSF) from the subarachnoid space via small structures called arachnoid granulations. This drainage system is essential for maintaining proper pressure and fluid balance within the skull before the blood and CSF are returned to the internal jugular veins.
When the Dura Mater is Compromised
Injury to the dura mater can lead to significant neurological consequences, often involving blood accumulation or fluid leakage. A common pathological concern is a subdural hematoma, which occurs when blood collects in the space beneath the dura mater, typically tearing small “bridging” veins that cross this area. This condition is most often caused by a head injury that causes the brain to shift suddenly, stretching and tearing these delicate vessels.
The resulting blood collection puts pressure on the underlying brain tissue, which can be life-threatening if not treated promptly. Subdural hematomas are classified as acute, where symptoms develop within hours or days of a severe injury, or chronic, which may follow a minor injury and have symptoms that develop gradually over weeks. Older adults are particularly susceptible to chronic subdural hematomas because age-related brain shrinkage stretches the bridging veins, making them more vulnerable to rupture.
Another serious complication is a dural tear, which can happen after trauma, surgery, or sometimes spontaneously, causing a cerebrospinal fluid (CSF) leak. The tear allows the CSF, which cushions the brain, to escape, leading to low pressure within the skull. The most characteristic symptom of a CSF leak is a severe headache that worsens significantly when a person sits or stands up and is often relieved when lying flat. This “orthostatic headache” occurs because the brain loses its buoyancy and sags, pulling on pain-sensitive structures.