Structure and Functions of the Dura Mater

The literal translation of 'dura mater' is tough mother. It is an apt name, as the dura mater is the toughest of the meninges, which are the three membranes that protect the brain and the spinal cord from mechanical injury. In Latin, 'mater' means mother.

The translation of 'arachnoid mater' and 'pia mater', which are the other two meninges, is spider-like mother and tender mother respectively.

Dura mater, which is also referred to as pachymeninx, is one of three cranial meninges or membranous coverings that envelop the brain and the spinal cord. The other two meninges are called arachnoid mater and pia mater. Together, the pia mater and arachnoid mater are referred to as the leptomeninges.

The dura mater is a dense and tough membrane that is made up of bundles of collagen fibers that run in different directions. It lies close to the innermost layer of the skull. The main function of the meninges is to protect the brain from damage in the event of injuries.

While the skull protects the brain from blunt force trauma, the meninges protect the brain from getting damaged due to contact with the inside of the skull. Moreover, these provide a framework for the blood vessels, and contain cerebrospinal fluid, which also plays an important role in protecting the brain from mechanical damage.

Dura mater comprises two layers, which are called periosteal (endosteal) layer and the meningeal layer. Endosteal layer is the outer, periosteal layer that covers the inner surface of the skull. The periosteal and the inner meningeal layer are joined, with the exception of places where dural venous sinuses or the dural folds are present.

While the meningeal layer is continuous with the dura mater of the spinal cord, the periosteal layer does not extend through the foramen magnum (a large opening in the occipital bone of the skull) to become continuous with the dura mater of the spinal cord. These layers also provide tubular sheaths for the cranial nerves.

➠ The partitions of the dura mater, which are attached to the inner lining of the skull, provide support to the brain. Also, these folds restrict the rotatory displacement of the brain.

➠ The dura mater also provides a supporting framework for the dural venous sinuses that return deoxygenated blood from the brain to the heart.

While falx cerebri is a sickle-shaped fold of dura mater that separates the brain in two cerebral hemispheres, the tentorium cerebelli is a crescent-shaped fold that covers the cerebellum, and separates the occipital lobes of the cerebrum from the cerebellum.

The front end of the falx cerebri is attached to the internal frontal crest and crista galli, whereas its posterior end is attached to the upper surface of the tentorium cerebelli. Three venous sinuses that are present in this dural fold include straight sinus, superior petrosal sinus, and transverse sinus.

While straight sinus is located along the attachment of the tentorium fold to the falx cerebelli (sickle-shaped dural fold extending down from the tentorium cerebelli between the two cerebral hemispheres), the superior petrosal sinus and transverse sinus are located along the attachment of the tentorium to the petrous bone and occipital bone, respectively.

Diaphragma sellae is another dural fold that covers sella turcica, which is a small saddle-like cavity or depression in the skull. It is through the small opening present in its center that the stalk of the pituitary gland passes.

The branches of the following arteries supply blood to the dura mater:

➠ Internal carotid artery
➠ Middle meningeal artery
➠ Maxillary artery
➠ Ascending pharyngeal artery
➠ Occipital artery
➠ Vertebral arteries

The venous drainage of the meninges includes the meningeal veins of the dura and the dural venous sinuses. The meningeal veins and the bridging veins (veins that drain the neural tissues lying underneath) empty into the dural sinuses. Dural venous sinuses are venous channels that carry blood from the brain to the heart.

These venous channels receive blood from several veins in the brain and empty into the internal jugular vein, from where the blood is returned to the right atrium of the heart via superior vena cava. The dural venous sinuses also receive cerebrospinal fluid from the subarachnoid space.

The venous channels present in the dura mater include:

➠ Superior sagittal sinus
➠ Inferior sagittal sinus
➠ Straight sinus
➠ Transverse sinuses
➠ Cavernous sinuses
➠ Sigmoid sinuses
➠ Inferior petrosal sinus
➠ Superior petrosal sinus
➠ Sphenoparietal sinuses
➠ Occipital sinus

The potential space between the dura mater and the arachnoid mater, which is the second membrane that is located in the middle, is referred to as the subdural space. The pia mater is the innermost membrane that adheres to the surface of the brain.

Subarachnoid space, which is the space between the arachnoid and pia mater, is filled with cerebrospinal fluid, a clear fluid that is produced by the choroid plexus located in the ventricles (hollow cavities in the brain). The cerebrospinal fluid flows around and within the brain, acting like a protective cushion.

Anatomists are of the view that the epidural and subdural spaces are not naturally present, but might develop as a result of tissue damage. These spaces might get filled with blood in the event of rupturing of blood vessels.

The conditions associated with the accumulation of blood in the epidural and subdural spaces are referred to as epidural and subdural hematomas, respectively. While the former occurs due to the rupturing of the middle meningeal artery, the latter usually occurs due to the rupturing of veins that drain blood away from the surface of the brain.

Closed head injuries that cause epidural hematomas are more likely to affect adults, whereas children are more prone to subdural hematomas due to head trauma. Besides hematomas, other conditions associated with the dura mater include spontaneous cerebrospinal fluid leakage due to perforations in the dura mater and dural ectasia (enlargement of the dura).

On a concluding note, the dura mater performs the vital function of protecting the central nervous system. An interesting fact about the dura mater is that unlike other parts of the brain, the dura mater is sensitive to pain, as it is innervated by trigeminal nerve, vagus nerve, and the first three cervical nerves. It is also supplied by the branches from the sympathetic nervous system.