Meninges of Brain

Introduction 

The brain is very important delicate organ. it is protected by the following coverings. 

1. Bony covering of the cranium.
2. The middle arachnoid mater. (meninges) : 

     a. The outer dura mater (Pachymeninx)

     b. The middle arachnoid mater.

     c. The inner pia mater . 

Meninges

     Dura mater  : The dura mater is the outermost, thickest and toughest membrain covering the brain. (Dura = Hard) ( mater = mother) 

Dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. 

There are two layers of dura : 

a. An outer and endosteal layer which searves as an internal endoosteam and periosteum or endocranium for the skull bone.

b. An inner or meningeal layer which surrounds the brain. The meningeal layer is continuous with the spinal dura mater.

The two layers are fused to each other atall places, except wheren the cranial venous sinuses are enclosed between them. 

Dura mater. 

 

Arachnoid mater : The middle element of the meninges is the arachnoid mater, so named because of its spider web-like appearance.This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid.

Cerebrospinal fluid (CSF) flows under the arachnoid in the subarachnoid space.

Pia mater : The pia ( latin : loving mother) mater is a thin vascular membrain which closly investes the brain, diping into the various sulci and other irregularities of its surface. it comparises  epi-pia and pia-glia. On the cerebrum pia mater dips and forms fold in relation to larger fissures of cerebellum.

Functions of Pia mater : 

1.CSF production and circulation

2.Perivascular spaces (Pia mater allows for the formation of perivascular spaces that help serve as the brain’s lymphatic system.) 

3.Permeability (Due to the pia mater’s and the ependyma's high permeability, water and small molecules in the CSF are able to enter the brain interstitial fluid, so the interstitial brain fluid and the CSF are very similar in terms of composition)

Clinical anatomy

• Injuries involving the meninges, can result in a hemorrhage and two types of hematoma . 
• A subarachnoid hemorrhage is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma
• An epidural hematoma, bleeding between the dura mater and the skull, may arise after an accident or spontaneously.