Dura mater (Dura mater)
The outermost and densest membrane. Within the cranial cavity, it consists of two tightly adhered layers. Separation occurs only at the outer margin of the foramen magnum:
- The outer layer continues as the periosteum of the vertebral canal.
- The inner layer continues to envelop the spinal cord, forming the dural sac, which ends at the level of the second sacral vertebra. The filum terminale departs from it, weaving into the coccygeal ligament.
Between these layers in the vertebral canal, the epidural space is formed, filled with adipose tissue and the internal vertebral venous plexus.
The inner layer of the cranial dura mater forms dural folds that compartmentalize the brain:
- Falx cerebri (falx cerebri) — located between the cerebral hemispheres.
- Tentorium cerebelli (tentorium cerebelli) — separates the cerebrum from the cerebellum.
- Falx cerebelli (falx cerebelli) — separates the cerebellar hemispheres.
- Diaphragma sellae and the wall of Meckel's cave (housing the trigeminal ganglion).
Blood supply and innervation of the dura mater
The arteries of the dura mater are characterized by a large caliber. The most massive of them is the middle meningeal artery (a branch of the maxillary artery), which enters the skull through the foramen spinosum and supplies the entire lateral surface of the vault. The anterior meningeal artery (from the internal carotid system) supplies the area above the frontal lobes, and the posterior artery (passing through the jugular foramen) supplies the posterior cranial fossa.
Clinically important is the anastomosis in the orbit: the middle meningeal artery connects with the lacrimal artery. If the ophthalmic artery becomes occluded proximal to the origin of the central retinal artery, this anastomosis can preserve blood supply to the eye.
Innervation:
- Above the tentorium cerebelli, the dura is innervated by the trigeminal nerve.
- Below the tentorium, it is supplied by branches of the vagus nerve and upper cervical spinal nerves.
Nerve endings here respond to stretch. Mechanical stimulation causes sharp and conscious pain, with the fibers wrapping around the meningeal arteries being the most sensitive.
Arachnoid and pia mater
The arachnoid mater (Arachnoidea mater) is a thin membrane completely devoid of blood vessels. It lies adjacent to the dura mater, and beneath it lies the subarachnoid space, filled with cerebrospinal fluid (CSF). Where the arachnoid bridges over deep sulci, the space expands, forming cisterns (for example, the cerebellomedullary cistern). The subarachnoid spaces of the skull and the spinal canal communicate through the foramen magnum.
The pia mater (Pia mater) consists of mesodermal cells. It is tightly fused to the brain tissue via a glial membrane formed by astrocytes, precisely following the contours of all gyri.
Vessels penetrating the brain are surrounded by funnels of pia mater, thus forming Virchow-Robin spaces. Unlike the dura mater, the nerves of the pia mater do not sense mechanical irritation or temperature, responding exclusively to stretching of the vessel wall.
Optic nerve sheaths
The optic nerve, as an outgrowth of the brain, is also surrounded by the pia, arachnoid, and dura maters. The dura mater enters the orbit: its outer layer becomes the orbital periosteum, while the inner layer envelops the nerve and fuses with the sclera of the eye.
Around the nerve, the perioptic subarachnoid space is formed, which directly communicates with the cranial cavity. When intracranial pressure rises, CSF rushes here, stretching the dura mater, which leads to papilledema. Similarly, in subarachnoid hemorrhage, blood can penetrate the sheaths of the eye.
Briefly: answers to topical questions
What cisterns are present in the subarachnoid space of the brain?
The subarachnoid space of the brain contains the basal cisterns and other expansions. These include:
- Cerebellomedullary cistern (cisterna cerebellomedullaris / cisterna magna) — the largest, located between the posterior margin of the cerebellum and the medulla oblongata.
- The interpeduncular cistern (cisterna interpeduncularis) is located between the pedunculi cerebri.
- The chiasmatic cistern (cisterna chiasmatis) is located anterior to the chiasma opticum.
- Cistern of the lateral fossa of the cerebrum (cisterna fossae lateralis cerebri) — located in the corresponding sulcus/fossa.
Other notable cisterns include the interhemispheric, transverse, ambient, pontine, and cistern of the vermis.
What branches does the middle meningeal artery give off?
The middle meningeal artery (a. meningea media) divides into two main branches. These include:
- Frontal branch — supplies the dura mater.
- Parietal branch — also participates in the vascularization of the meninges.
These branches supply most of the dura mater. Additionally, the middle meningeal artery anastomoses with the lacrimal artery (a branch of the ophthalmic artery) in the orbit, which is clinically significant in cases of ophthalmic artery occlusion.
What passes through the jugular foramen?
Through the jugular foramen (foramen jugulare) pass cranial nerves, blood vessels, and neural ganglia. The contents of the foramen include:
- Glossopharyngeal nerve (CN IX) — passes along with its superior and inferior ganglia.
- Vagus nerve (CN X).
- Accessory nerve (CN XI).
- Posterior meningeal artery (a. meningea posterior) — enters the cranial cavity to supply the dura mater.
- Veins — participate in venous drainage.
Which ligaments fix the spinal cord within the dural sac?
The spinal cord is fixed within the dural sac by the denticulate ligament (ligamentum denticulatum), which is a derivative of the pia mater (pia mater spinalis) and anchors the spinal cord.
The order of the meninges from outside to inside is easily remembered by the acronym DAP: Dura, Arachnoid, Pia.
Class and exam questions
Does the arachnoid mater have its own blood vessels?
No, the arachnoid mater is entirely avascular (devoid of blood vessels). Major arteries run beneath it in the subarachnoid space.
Why does papilledema occur when intracranial pressure rises?
The optic nerve is surrounded by the same three meninges as the brain. Elevated cerebrospinal fluid pressure is transmitted into the perioptic space, causing stretching of the retrobulbar portion of the dura mater.
What is located in the epidural space?
The epidural space is located in the vertebral canal between the periosteum and the inner layer of the dura mater. It contains connective tissue bundles, adipose tissue, and the internal vertebral venous plexus.
What else to study on this topic
- Anatomy and contents of Meckel's cave
- Topography of the subarachnoid cisterns of the brain
- Structure of Virchow-Robin spaces
- The ventricular system of the brain and cerebrospinal fluid circulation
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