The brain, although it is a powerful organ, is in itself quite vulnerable when it comes to structure: if traumatized, it would bruise very easily. The reason that it generally does not get injured except under extreme circumstances such as a car crash, is that is has several layers of protection which take the impact when the head is hit. As the picture below shows, the first layer underneath the skin and hair is the skull, and the layers underneath include the meninges. These layers are fused together and they act as both a cushion and a lubricant for the brain. There are other circumstances which make this barrier more of a curse than a blessing, but I’ll discuss those in Brain Pathology.
The meninges are composed of several layers, and they include the following: the dura mater, the pia mater, the arachnoid and the subarachnoid space. I’ll now discuss each of these as well as the skull individually. There is also another very important structure that protects the brain known as the blood-brain barrier, which I’ll discuss separately.
The dura mater is the layer of the meninges directly under the skull and is the thickest part of the meninges. The function of the dura mater is that it acts like an blanket for the deeper layers. There are two layers of the dura mater: the periosteal and the meningeal layers, and both of these layers are composed of dense fibrous tissue, with blood vessels interlaced within that submerge deeper into the meninges. There are also a layer of flattened cells and four layers of infolding within the dura. The layers of infolding are the falx cerebelli, the falx cerebri, the diapharagma sellae and the tentorium cerebelli and these infolds help to separate certain areas of the brain such as the cerebral hemispheres and to cover up other areas such as the pituitary gland.
The arachnoid mater is the middle layer of the meninges, and like the picture alongside suggests, it has a thin and spidery appearance. Like the above dura mater, it is composed of fibrous tissue and has a layer of flattened cells that fluid cannot penetrate. Unlike the dura mater, however, it does not fit tightly around the brain structures: rather, it is like a loose-fitting piece of clothing, because there are some areas that are attached and others that hang.
The pia mater is the final layer of the meninges and is the layer that attaches to the brain and the spinal cord. It is quite delicate, despite the fact that is made of fibrous tissue, because of how thin it is. Like the layers above it, it is covered by a layer of flattened cells, and the blood vessels that originated in the dura mater split into capillaries and permeate the pia mater.
The subarachnoid space is the area which contains cerebrospinal fluid and is considered part of the ventricular system. The CSF, as well as acting as a cushion for the brain. It also provides buoyancy for the brain (it helps its blood vessels and neurons being crushed under the brain’s weight) and as a waste-disposal unit: waste from the CNS gets transferred outside of the blood-brain barrier via the CSF.
The skull is composed of bone and is made up of two layers: the cranium and the mandible. It not only provides protection for the brain, but it also provides space for the eyes and helps fix the position of the ears. It is made up of flat bones, and each of these bones are joined together by sutures. The names of each of the bones is similar to that of the corresponding brain lobes underneath, as seen by the picture below.