The meninges are the membranous coverings of the brain and spinal cord. There are three layers of membranes called dura mater, arachnoid mater and pia mater.
Functions of meninges:
The three layers of Meninges are: Dura mater, Arachnoid mater, Pia mater
It is the outermost layer of meninges and located just below the cranial bones and the vertebral column. It is thick, tough and inextensible. Dura mater consists of two layers of sheets of connective tissue –
Periosteal layer – lines the inner surface of the cranial bones
Meningeal layer – located very close to periosteal layer but this layer continues to the dura mater of spinal cord.
Dura mater consists of its own blood supply and drainage of arteries and veins. Its nerve supply is by trigeminal nerve.
Dural reflections are formed when the membrane of dura mater folds inwards upon itself. There are four dural reflections.
The arachnoid mater is the middle layer of the meninges that lies under the dura mater. It does not have any blood or nerve supply and consists of layers of connective tissue. The space under the arachnoid mater is called subarachnoid mater and contains cerebrospinal fluid (CSF). Arachnoid mater projects into the dura mater to allow the CSF to circulate through the dural venous sinuses.
Pia mater is located right underneath the sub-arachnoid space. It is very thin layer and tightly clings along the surface of the brain and spinal cord, following the contours of the brain.
It has a complex network of blood supply and nerve supply.
The subarachnoid space consists of cerebrospinal fluid that runs along the brain to the spinal cord. This fluid helps in maintaining temperature and also acts as a cushion to protect the brain from mechanical damage.
Problems in meninges and CSF can cause severe headaches and infection of the same can result in serious complications. Hematomas and meningitis are the more common problems of the meninges.
- Extradural and Subdural hematomas: Hematoma is a collection of blood and this can cause rapid increase in intra-cranial pressure. Extradural is collection of blood between the skull bone and dura mater and subdural hematoma is the collection of blood between dura and arachnoid mater. Either of them, when they exert pressure over the skull or the brain tissues, can be fatal if untreated.
- Meningitis: It is the inflammation of the meninges and is usually caused by virus or bacteria. When the body responds to the bacterial or viral infection by producing antibodies, it also results in cerebral edema and thus increases the intracranial pressure. This can lead to a part of the brain to get squeezed out of the cranial cavity. Intracranial pressure can also result in reduction in blood flow to the brain. Both the conditions can result in sudden death of the person.