- What are the meninges?
- Where are the meninges located?
- What function do the meninges have?
- What problems can the meninges cause?
The meninges are three closely spaced covers around our brains. Between them is liquor (cerebrospinal fluid) and blood vessels. The meninges form a protection for the brain against mechanical influences and larger temperature fluctuations. Read here everything important about the structure and function of the three meninges Dura mater, Arachnoidea and Pia mater!
What are the meninges?
The three meninges are connective tissue layers that surround the brain. They develop from the embryonic neural tube. The meninges are called from outside to inside:
- Dura mater (hard meninges)
- Spiderweb Skin (Arachnoidea)
- Pia mater (soft meninges)
The dura mater is the outermost of the three meninges and quite tight. It dresses the cranial cavity and consists of two layers: connective tissue and a low, inner epithelial layer. The outer layer, in which vessels run, which supply the skull bone, is at the same time the periosteum of the skull bone.
This periosteum has grown into the skull bone until adolescence. This ensures that the child's skull, whose individual bones are still separated by soft sutures, can not deform. In adults, the periosteum can be easily detached from the bone - only at the base of the skull is it always firmly connected to the bone.
The dura mater also forms duplications projecting separating between the two cerebral hemispheres and between the cerebrum and cerebellum: cerebral sickle (falx cerebri), the cerebellum sickle (falx cerebelli) and the cerebellum tent (tentorium).
The two cerebral sinews separate the two cerebral hemispheres deeply in the middle of the skull, down to the beam.
The cerebellum tent (Tentorium cerebelli), on the other hand, is transversely positioned and separates the cerebrum from the cerebellar hemisphere. This dura mater duplication merges into the portion of the dura mater that lines the inner skull bone. Below the tentorium cerebelli lies the cerebellum in the posterior fossa; The brainstem passes through a small section.
At three points, the dura mater into two leaves on: (in which the inner ear is located) encloses the ganglion of the petrous trigeminal (a node from nerve cells and fibers of the trigeminal nerve); at the tip of the petrous pyramid it encloses the endolymphatic sac (sensory cells for the organ of equilibrium); in the area of Sella turcica (Turkish saddle) it includes the pituitary gland.
Under the dura mater is a narrow space, the subdural space, which the dura mater of the middle of the three meninges, the arachnoid (arachnoid), separates.
The arachnoid membrane is composed of connective tissue, is avascular and connects to the inside through small trabeculae and membrane with the underlying inner mater, the pia mater soft. Outwardly, to the dura mater, the arachnoid forms a closure membrane for the cerebrospinal fluid, which can not pass this limit.
The arachnoid lies smoothly on the brain surface, it goes over the furrows and depressions of the brain in the area of the entire domed calvarium. Due to bony elevations and depressions, cistern-like extensions are formed only at the brain base.
The arachnoid forms villous connective-tissue, vascular anachalias (arachnoid villi) that extend into the dura mater, veins, and cranial bones. The cerebrospinal fluid is absorbed from the subarachnoid space via these arachnoid villi and released into the blood.
The third layer of the meninges, the pia mater, is located directly on the brain, followed by the grooves and recesses of the cerebrum and cerebellum, and performs the vessels and nerves that lead into the brain. The pia mater also reaches into the brain chambers.
Where are the meninges located?
The meninges are connective tissue layers that surround the entire brain. At the foramen magnum, the large occipital hole in the posterior fossa, there is a connection to the spinal canal. Here, the meninges go over into the spinal cord skins.
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What function do the meninges have?
The dura mater as the outermost of the three meninges protects the skull against deformations with its outer layer in the growth phase. The inner layer delimits the subdural space from the outside and records fluctuations in the volume of the brain resulting from the pulse and respiration.
The three septa of the dura mater (Falx cerebri, Falx cerebelli and Tentorium cerebelli) ensure the position of all parts of the brain in every position of the body like a brace within the skull.
The arachnoid - the middle of the three meninges - forms a barrier to the CSF space, which seals it to the outside.
The pia mater as the innermost meninges forms the plexus choroidei by invagination in the cerebral ventricles together with parts of the nerve tube. These vascular bundles in the ventricles from the cerebrospinal fluid.
What problems can the meninges cause?
An epidural hematoma is a bruise of arterial bleeding between the dura mater and the skull bone resulting from skull injury. 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 of the tentorium cerebelli at birth.
A subarachnoid hemorrhage is a bleeding in the subarachnoid space - the gap-shaped space between the two inner meninges, arachnoid and pia mater. It often results from the rupture of an aneurysm (circumscribed vascular dilation). Symptoms include severe headache, hypotension and an increase in intracranial pressure due to the space-occupying bleeding.
Open skull injury associated with injury to the dura mater may result in CSF formation. It is a connection between the CSF space and the outside world. Through them, germs can invade the brain. Signs of CSF is the leakage of cerebrospinal fluid from the nose or ear canal.
Arachnoid cysts are malformations of the arachnoid with chambered fluid collections. They are usually caused by a subarachnoid hemorrhage during birth or meningitis (meningitis) in the first years of life. Arachnoid cysts damage the underlying brain tissue by pressure.
As Meningitis doctors refer to an inflammation of the meninges, which is triggered by bacteria, viruses, fungi, parasites or radiation damage. At the same time, the brain tissue itself can be inflamed (encephalitis) - which together is called meningoencephalitis.
Meningism is a symptom that resembles meningitis but has a different cause. These include headache, backache, cramps, neck stiffness and fever. Meningism often occurs as a concomitant of febrile illnesses.
Meningiomas are found in brain tumors that have their origin in one of the brain tumors meningeswho have arachnoidia. They adhere to the dura mater over a wide area and grow into brain tissue. Meningiomas can be benign or malignant.