The dura mater (hard meninges) serves essentially to protect the brain from external influences. It is one of three meninges that surround the human brain. This three-layered meninges (meninx encephali) consists of connective tissue and merges in the spinal canal into the so-called spinal cord skin. The hard meninges are particularly taut, lie on the outside and have blood vessels in their invaginations. These can transport blood out of the brain. In addition, the dura mater contains many pain receptors, which is why it is very sensitive.
What is the dura mater?
The meninges further include the soft meninges (pia mater), which are mainly responsible for supplying nutrients to the brain tissue. Between the hard and soft meninges lies the cobweb (arachnoid mater). It has many smaller blood vessels and is also responsible for the exchange between cerebrospinal fluid (CSF) and blood. With the help of the spaces between the three meninges, shocks and also changes in brain volume can be compensated. Physiologically, there is no space between the hard meninges and the bones of the skull. This is because the dura mater consists of two so-called sheets. The outer sheet of the hard meninges is also the inner periosteum of the skull. Again, the inner leaf of the dura mater connects very snugly with the cobweb skin. However, due to hemorrhage or trauma, an epidural space can develop there, which may be composed of loose connective tissue, fat, veins, and lymphatic vessels. If necessary, injections can be given into this cleft space to numb the exiting nerve roots. Over the larger fissures of the brain, the hard meninges form so-called durasepts, often tent-like linings. The largest septum extends in the shape of a crescent in the upper skull and separates the two cerebral hemispheres. Likewise, both sections of the cerebellum are also separated by a duraseptum. In addition, the dura mater is capable of forming venous blood collection vessels that drain blood from the meningeal layers and the brain toward the heart.
Anatomy and structure
Blood is supplied to the entire meninges by three arteries that branch from the external carotid artery. The fifth cranial nerve provides sensitive supply to the meninges. It is also responsible for the pain and pressure sensitivity of the human face. This is the reason for the very high sensitivity of the hard meninges in particular. It has the decisive importance for the processing of pain stimuli in the head. Pain is very often caused by increased pressure on the meninges. Bleeding in the brain can be an important cause. Similarly, meningitis (inflammation of the meninges) causes severe pain in the head. Meningitis is brought on by viruses, bacteria or, less commonly, fungi. The more the immune system is weakened, the more easily they cause meningitis. Viruses are more common as the causative agent of meningitis, but bacteria are more dangerous in this regard.
Function and tasks
Bacterial meningitis can lead to life-threatening conditions in the course of a few hours and to rapid death soon after. In the event of survival, permanent mental disability is not an exception. Triggers are often meningococci or pneumococci. Meningitis usually begins with sudden flu symptoms such as fever, aching limbs and headache, and also chills. A little later, however, symptoms such as a stiff neck and specifically pain when moving the head to the chest become apparent. During this process, the meninges are stretched, which causes severe pain due to their inflammation. The affected person may also experience photophobia. If these signs occur, a doctor should be consulted immediately. Children and, if necessary, infants should be vaccinated against meningitis in a timely manner. Bacterial meningitis usually requires hospitalization. Both the patient and all contacts are treated with antibiotics. If treatment against meningitis begins early, the disease usually heals without consequences. Only in rare cases does hearing damage or various signs of paralysis remain. In addition, there may be conspicuous behavioral changes once the meningitis has reached the brain.
Diseases
Because the collagenous connective tissue that makes up the dura mater is particularly tight, it is relatively easy for entrapments to occur in various areas of the brain. These entrapments occur primarily in the so-called durasepts. They are mainly caused by hemorrhages, tumors or other space-occupying changes in the cranial fossa. A distinction is made between axial and lateral entrapments. Axial entrapment is a symmetrical entrapment that spreads equally in both cerebral hemispheres. The upper axial entrapment exerts pressure on the midbrain, the lower on the brainstem. In contrast, lateral entrapment occurs in the unilateral space-occupying processes. It brings with it the danger that the cerebral peduncles are pushed away to the opposite side, which can lead to more or less severe brain damage there. If the inflammation of the meninges spreads to the brain itself, it is a so-called meningoencephalitis. The three meninges can also be affected by nervous irritations in the area of the head. They have in common occurring headaches, persistent sensitivity to light and strong noises, and often also nausea and vomiting. These complaints are also seen in other diseases of the meninges such as migraine or subarachnoid hemorrhage. This hemorrhage often occurs after accidents or pressures on the brain that damage the spaces between the meninges by causing bleeding.
