Answer
The meninges are connective tissue coverings of the brain and spinal cord. They include the dura mater, the arachnoid mater, and the pia mater which are positioned between cranial bones and the neural tissue of the CNS.
The dura mater
In the brain the dura mater has two layers: the outer, periosteal layer (periosteum,) approximates the cranial bone, but does not continue into the vertebral column. The inner, meningeal layer continues into the vertebral column, and forms the dural sheath around the spinal cord (SC).
The layers of the dura are pressed close together and against the cranial bones. However, there are spaces where the two layers of the dura are separated. These dural spaces or dural sinuses collect blood that has circulated through the brain. The superficial sinuses are the superior sagittal sinus and the transverse sinus. These sinuses meet at the back of the head and conduct venous blood to the internal jugular veins in the neck. Other important dural sinuses are the straight sinus, the sigmoid sinus and the occipital sinus.
The arachnoid mater and the pia mater of the brain are similar to those in the spinal cord. :
The arachnoid mater is a transparent covering between the dura mater and the pia mater. A space exists between the pia and the arachnoid : this is the subarachnoid space. . In some places there is also a subdural space which separates the arachnoid and the dura
The pia mater (pia) is very thin and delicate. It closely invests the brain neural tissue, follows the folds and dips into sulci in some places
Work Step by Step
The subarachnoid space has channels which contain cerebrospinal fluid (CSF). The CSF acts as a cushion to protect the brain and spinal cord, physically. It also brings nutrients and oxygen to CNS tissue, and removes carbon dioxide and metabolic wastes.
