Meninges
Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.
More about the experts All content is checked by medical journalists.The meninges are three closely spaced layers around our brain. Liquor (cerebrospinal fluid) and blood vessels run between them. The meninges protect the brain from mechanical influences and from major temperature fluctuations. Read everything you need to know about the structure and function of the three meninges dura mater, arachnoid and pia mater!
What are the meninges?
The three meninges are layers of connective tissue that enclose the brain. They develop from the embryonic neural tube. The meninges are called from the outside in:
- Dura mater (hard meninges)
- Spider web skin (arachnoidea)
- Pia mater (soft meninges)
Dura mater
The dura mater is the outermost of the three meninges and is quite tight. It lines the cranial cavity and consists of two layers: connective tissue and a low, inner epithelial layer. The outer layer, in which the vessels that supply the skull bone run, is also the periosteum of the skull bone.
This periosteum is still firmly attached to the skull bone into adolescence. This ensures that the child's skull, whose individual bones are still separated by soft sutures, cannot deform. In adults, the periosteum can then be easily detached from the bone - only at the base of the skull does it always remain firmly attached to the bone.
The dura mater also forms duplicates that project between the two halves of the cerebrum and between the cerebrum and cerebellum: the cerebral sickle (Falx cerebri), the cerebellar sickle (Falx cerebelli) and the cerebellar tent (tentorium cerebelli).
The two cerebral sickles separate the two cerebral hemispheres deeply from each other in the middle of the skull, down to the bar.
The cerebellar tent (tentorium cerebelli), on the other hand, is positioned transversely and separates the cerebral and cerebellar hemispheres. This dura mater duplication merges into the part of the dura mater that lines the inner skull bone. The cerebellum lies beneath the tentorium cerebelli in the posterior fossa; the brain stem passes through a small section.
The dura mater divides into two sheets in three places: At the petrous pyramid (in which the inner ear is located) it encloses the trigeminal ganglion (a knot of nerve cells and fibers of the trigeminal nerve); At the top of the petrous pyramid, it encloses the endolymphatic sac (sensory cells for the organ of equilibrium); in the area of the sella turcica (Turkish saddle) it includes the pituitary gland (pituitary gland).
Under the dura mater there is a narrow space, the subdural space, which separates the dura mater from the middle of the three meninges, the arachnoid.
Arachnoid
The arachnoid consists of connective tissue, is vascular and connects on the inside via small trabeculae and membranes with the underlying, inner meninges, the soft pia mater. To the outside, to the dura mater, the arachnoid forms a closing membrane for the liquor, which cannot pass this border.
The arachnoid rests smoothly on the surface of the brain, it passes over the furrows and depressions of the brain in the area of the entire arched skullcap. Cistern-like expansions are only formed at the base of the brain, due to bony elevations and depressions.
The arachnoid forms villi-like connective tissue, vascularless outgrowths (arachnoid villi) that extend into the dura mater, veins and also into the cranial bones. The liquor is absorbed from the subarachnoid space via these arachnoid villi and released into the blood.
Pia mater
The third layer of the meninges, the pia mater, lies directly on the brain, follows the furrows and depressions of the cerebrum and cerebellum and guides the vessels and nerves that lead into the brain. The pia mater also extends into the chambers of the brain.
Where are the meninges located?
The meninges are layers of connective tissue that enclose the entire brain. There is a connection with the spinal canal at the foramen magnum, the large occipital opening in the posterior fossa. Here the meninges merge with the membranes of the spinal cord.
What is the function of the meninges?
The outer layer of the dura mater, the outermost of the three meninges, protects the skull from deformation during the growth phase. The inner layer delimits the subdural space from the outside and absorbs fluctuations in volume of the brain caused by pulse and breathing.
The three septa of the dura mater (falx cerebri, falx cerebelli and tentorium cerebelli) secure the position of all parts of the brain in every position of the body like a strut within the skull.
The arachnoid - the middle of the three meninges - forms a barrier for the liquor space, which it seals off from the outside.
The pia mater as the innermost meninges forms the choroid plexus by invagination into the cerebral ventricle together with parts of the nerve tube. These vascular clusters secrete the liquor in the ventricles.
What problems can the meninges cause?
An epidural hematoma is a bruise from arterial bleeding between the dura mater and the skull bone that occurs after skull injuries. The space-occupying bleeding leads to a bruising of the brain.
A subdural hematoma is caused by venous bleeding between the meninges dura mater and arachnoid, or by a tear in the tentorium cerebelli under birth.
Subarachnoid hemorrhage is bleeding in the subarachnoid space - the gap-shaped space between the two inner meninges, the arachnoid and pia mater. It often arises from the rupture of an aneurysm (circumscribed vasodilatation). Symptoms are severe headaches, a drop in blood pressure and an increase in intracranial pressure due to the space-occupying bleeding.
A CSF fistula can form due to open injuries to the skull that are associated with an injury to the dura mater. This is a connection between the liquor space and the outside world. Germs can enter the brain through them. A sign of a liquor fistula is the leakage of liquor from the nose or the ear canal.
Arachnoid cysts are malformations of the arachnoid with chambered accumulations of fluid. They usually arise from subarachnoid hemorrhage during childbirth or from meningitis in the first few years of life. Arachnoid cysts cause pressure to damage the underlying brain tissue.
Meningitis is an inflammation of the meninges caused by bacteria, viruses, fungi, parasites or radiation damage. At the same time, the brain tissue itself can be inflamed (encephalitis) - which is collectively referred to as meningoencephalitis.
Meningism is a symptom that is similar to meningitis but has a different cause. These include headache and back pain, cramps, stiff neck, and fever. Meningism often occurs as a side effect of febrile illnesses.
Meningiomas are tumors in the brain that have their origin in one of the meninges called the arachnoid. They adhere to the dura mater over a wide area and grow into brain tissue. Meningiomas can be benign or malignant.
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