Meninges
(New Aug 2006)

Meninges

Cross section of skull/brain/meninges Apart from the scalp and skull there are three other layers inside the skull that encase and protect your brain. These coverings together are the meninges, and consist of the "Dura Mater", the "Arachnoid", and the "Pia Mater". Not surpisingly, like most medical nomenclature it is derived from Greek, even though the meninges were not identified and labelled until the Renaissance.

Dura Mater

The Dura mater or "Tough Mother" is the outside fibrous leather-like layer that truly protects the brain. Apart from actually encasing the brain, it is also fused to the skull at a number of points, and therefore also restricts and anchors the movement of the brain within the skull. The dura mater also separates and partitions the brain as a more efficient method of securing the brain to the skull, with each of the two hemispheres, and the cerebellum being encased separately.

Arachnoid

The Arachnoid or "spider-like" covering is the middle layer of the three meninges and is laced throughout with blood vessels, looking like a spider's web, hence its name. The arachnoid is secured to the dura mater and therefore closely adhres to it, in contrast to being more separated from the pia mater. The space between the pia mater and arachnoid is where the cerebro-spinal fluid (CSF) is largely contained and called the sub-arachnoid space. It is this sack of fluid that protects or at least minimizes damage to the brain from impacts to the skull.

Pia Mater

The Pia Mater, or "Soft Mother" is the innermost layer of the meninges, and closely adheres to the brain like a very fine and delicate sheet of saran wrap. It is also laced with finer blood vessels or capillary beds and is the brain's main supply of nutrients.

Pathology

Blunt force trauma to the head, often causes a rupture of the vasculature of the meningeal layers, or a brain bleed. The name of the brain-bleed often depends upon the location of where the blood pools. Thus, during a subarachnoid bleed, the ruptured blood vessel(s) leak into the space between the pia mater and arachnoid, and frequently can be detected by a pink tinge to the CSF. Conversely, a subdural hematoma, is a pooling of blood inthe tight space between the dura mater and the arachnoid, which can cause damage to the brain by swelling and putting pressure upon it. If caught early enough it is easily rectified by drilling a hole to this space and draining it, relieving the pressure and allowing the brain to come back to normal.

One of the other frequently heard conditions is meningitis, which is a viral or bacterial infection of the meninges, which causes them to become imflamed. Viral infections often subside withini a few days, but the bacterial infections can induce seizures and become life threatening. Although caused by a number of common bacteria, most meningitis can be treated with standard anti-biotics. Frequently meningitis has originated from other tissue immflamation like sinusitis or imlammation of the sinuses. The big fear behind bacterial meningitis is that it can be contagious and passed on in the same fashion as a cold or flu might be. Cross section of skull/brain/meninges