Arachnoid

Arachnoid

The arachnoid mater is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is situated between the dura mater and the pia mater, and plays a crucial role in the protection and support of the central nervous system.

Structure

The arachnoid mater is a delicate, web-like membrane that is avascular, meaning it lacks blood vessels. It is named for its spider web-like appearance. The arachnoid is composed of layers of connective tissue and is attached to the dura mater, the outermost meningeal layer, by a thin layer of cells.

Beneath the arachnoid mater lies the subarachnoid space, which contains cerebrospinal fluid (CSF) and the major blood vessels that supply the brain. The subarachnoid space acts as a cushion, protecting the brain and spinal cord from injury.

Function

The primary function of the arachnoid mater is to act as a barrier and a protective layer for the central nervous system. It helps to:

• Maintain the blood-brain barrier by preventing the passage of potentially harmful substances from the bloodstream into the brain.
• Facilitate the circulation of cerebrospinal fluid, which provides nutrients and removes waste products from the brain.
• Protect the brain and spinal cord from mechanical damage by acting as a shock absorber.

Clinical Significance

The arachnoid mater can be involved in various medical conditions, including:

• Arachnoid cysts: These are fluid-filled sacs that can develop between the arachnoid mater and the brain or spinal cord. They are often congenital and may cause symptoms depending on their size and location.

• Arachnoiditis: This is an inflammatory condition of the arachnoid mater, often caused by infection, surgery, or trauma. It can lead to chronic pain and neurological deficits.

• Subarachnoid hemorrhage: This is a serious condition where bleeding occurs in the subarachnoid space, often due to a ruptured aneurysm. It can lead to severe headaches, neurological damage, and is a medical emergency.

See Also

• Meninges
• Dura mater
• Pia mater
• Cerebrospinal fluid

References

• Susan,

 Gray's Anatomy: The Anatomical Basis of Clinical Practice, 
 41st edition, 
 Elsevier, 
 2016, 
  
  
 ISBN 978-0-7020-5230-9,

• Rengachary, Setti S.."The Meninges: Anatomy and Clinical Implications".Neurosurgery.2000;47(3)

707-721.doi:10.1097/00006123-200009000-00030.