The meninges are a layer of connective tissue that surrounds the brain. A distinction is made between three different meninges. In the spinal canal, the meninges continue as the spinal cord skin.
What is meninges
The meninges or meninges are located around the brain, and a total of three skins can be distinguished:
- The hard meninges (dura mater encephali).
- The cobweb skin (arachnoid membrane encephali) resp.
- The delicate meninges (pia mater).
The first description of the meninges goes back to Herophilos of Chalcedon, who lived around 300 BC. In addition, the meninges are also divided into extracranial and intracranial meninges, respectively. Intracranial are the meninges within the skull. Extracranial are those that continue as spinal meninges and surround the central nervous system.
Anatomy and structure
On the very outside is the so-called hard meninges (dura mater encephali), immediately followed by the spinal meninges (arachnoidea encephali). On the very inside lies the delicate meninges, also known as the pia mater encephali. Outside the skull, the meninges continue as the spinal meninges and surround part of the central nervous system. The outermost meninges are composed of two sheets that separate at certain points to form venous blood conduits (sinuses). These transport blood from the brain or meninges to the internal jugular vein. The outer leaf also forms the inner periosteum and the inner leaf fuses with the cribriform membrane. Accordingly, there is no space between the cranial bone and the dura mater, but trauma or hemorrhage can create a so-called epidural space. At larger clefts, the hard meninges form durasepts, with the largest septum being the falx cerebri, which separates the cerebral hemispheres. In addition, below the pituitary gland, the dura mater forms what is known as the diaphragma sellae or tentorium cerebelli, which is located between the occipital lobe (occipital lobe) of the cerebrum and the cerebellum. Beneath the dura mater lies the cobweb membrane, which is also involved in the formation of durasepts. Below the spider web membrane is the physiological subarachnoid space. This represents the outer cerebrospinal fluid space of the brain, in which the neural fluid flows, through which the spinal cord and the brain, respectively, are protected in case of possible impacts. The subarachnoid space is divided into connective tissue septa by which the spinal cord and the pia mater are connected. The pia mater is the innermost meningeal layer, which is immediately adjacent to the brain tissue and forms a connective tissue layer around the blood vessels. The meninges are supplied with blood by means of the anterior meningeal artery, the media meningeal artery, and the inferior meningeal artery.
Function and Tasks
The hard meninges protect brain tissue; in addition, their duplicators contain blood vessels through which blood drains from the brain. The spider’s web forms fine protuberances, also called pacchioni granulations. Through them, cerebrospinal fluid is reabsorbed from the subarachnoid space and delivered to the sinus veins. In the inner CSF space lies the choroid plexus, through which new CSF is constantly formed, so that the CSF is always renewed. Due to tight junctions, a barrier is created so that no blood components can enter the CSF. This is very important because many substances found in the blood would be toxic to the nerve tissue. In addition, the meninges also form the so-called blood-brain barrier, which controls which substances can reach the brain.
Diseases
A very well-known disease is meningitis or meningitis, which is transmitted by viruses and bacteria. Meningitis causes neck stiffness, nausea and vomiting, headache, fever, and dizziness. If inflammation of the brain spreads to the meninges, it is called meningoencephalitis. This inflammation either spreads from the meninges to the brain or vice versa. If meningoencephalitis is not treated in time, it can lead to severe damage to the brain. Other diseases related to the meninges are tumors that can be located in the meninges and are called meningiomas.Meningiomas are benign growths that press on the nerves coming from the brain or on the brain itself, which can lead to epileptic seizures and neurological deficits. Since the tumor grows very slowly, it is usually discovered relatively late. Irritation of the meninges can be detected by Brudzinski, Laségue or Kernig signs. Other symptoms that indicate meningeal irritation syndrome include headache, nausea and vomiting, or sensitivity to noise and light. One of the most common causes of meningeal irritation is migraine, which predominantly affects women. Migraine is a functional disorder of the meninges, the brain and the blood vessels, respectively, which is neurobiologically caused. A migraine is favored by certain factors (triggers). These include hormonal changes (e.g. ovulation), stress, certain foods (e.g. cheese, chocolate) or changes in the weather. Then pulsating, often one-sided headaches occur, as well as nausea, vomiting or sensitivity to light. Accidents can also cause subarachnoid hemorrhage, which describes bleeding into the spaces between the meninges. If a meningeal artery ruptures, hemorrhage also occurs. An epidural space then forms between the periosteum and the dura mater, causing hemiplegia. Rupture of the bridging veins can lead to subdural hematoma, which causes symptoms such as clouding of consciousness, headache, or dizziness.
