arachnoid mater/membrane, (parietal layer of leptomeninges)

Introduction

[Greek, arachne = spider, cobweb]

A delicate fibrous membrane composed of fibrous & elastic tissue that forms the middle of the three coverings of the central nervous system.

The arachnoid is not attached to the dura, but is held against the inner surface of the duraby the pressure of the CSF.

In a spinal puncture, dura mater & arachnoid are penetrated simultaneously as if a single layer. Their apposition is the dura-arachnoid interface, often erroneously referred to as the "subdural space."

CSF is located between the pia mater & the arachnoid mater.

In the cadaver, because of the absence of CSF, the arachnoid falls away from the inner surface at the dura & lies loosely on the spinal cord.

Pathology

• separation of the arachnoid mater from the dura mater may result in subdural hematoma

More general terms

• brain structure
• spinal cord structure

Additional terms

• spinal arachnoid mater

Component of

• meninges