The Meninges

1. Layers of the Meninges
2. The Dura Mater
3. Dural Folds
4. Dural Venous Sinuses
5. Intracranial Haemorrhage
6. Quiz

• The meninges consist of three membranes: dura, arachnoid and pia mater.
• The dura has two layers: periosteal and meningeal.
• The two layers of dura occasionally separate to form dural venous sinuses, while reflections of the meningeal layer form dural folds.
• Important dural folds to know are the falx cerebri and tentorium cerebelli.
• The dural venous sinuses drain into the internal jugular vein.
• Intracranial haemorrhages can be extradural, subdural, subarachnoid or intracerebral.
• Extradural haemorrhages arise from a meningeal artery, particularly the middle meningeal artery.
• Subdural haemorrhages arise from bridging veins.

Layers of the Meninges

The meninges are a series of connective tissue membranes which encapsulate the brain and spinal cord. They act as a supportive framework for the brain and create a space to hold the cerebrospinal fluid (CSF).

The meninges consist of three membranes:

• Dura Mater - the outermost thick, fibrous layer.
• Arachnoid Mater - a thinner intermediate layer.
• Pia Mater - a very thin and delicate layer, which is closely adhered to the grey matter of the brain.

Diagram - Layers of the meninges

Creative commons source by SVG by Mysid, original by SEER Development Team [1], Jmarchn [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Between the meningeal layers are two spaces:

• Subdural Space - a potential space between the meningeal dura and arachnoid mater. The subdural space is normally empty.
• Subarachnoid Space - the space between the arachnoid and pia mater. This space is filled with CSF and contains the cerebral vessels.

The Dura Mater

The dura mater has two layers:

• Periosteal Dura - the outer layer of dura, adhered to the inner table of bone. It is synonymous with the periosteum.
• Meningeal Dura - the inner layer of dura, adjacent to the arachnoid mater.

In most parts, these two layers of dura are closely adhered to each other. However, there are some places where these layers separate, giving rise to dural folds and dural venous sinuses.

Dural Folds

In some places, the meningeal dura reflects inwards and fuses to form dural folds. These are tough fibrous sheets which divide the cranial cavity into rigid compartments.

Important dural folds to note are:

• Falx Cerebri - runs within the longitudinal fissure of the brain to separate the cranial cavity in the sagittal plane. It attaches anteriorly to the crista galli of the ethmoid bone and posteriorly to the superior surface of the tentorium cerebelli.
• Tentorium Cerebelli - separates the occipital lobes and cerebellum. It runs in the transverse plane and is tented due to the attachment of the falx cerebri.

Diagram - Anatomical prosection showing the falx cerebri and tentorium cerebelli

Creative commons source by Rabjot Rai, Joe Iwanaga , Gaffar Shokouhi, Rod J. Oskouian, R. Shane Tubbs [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

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