ARACHNOID SHEATH Meaning and
Definition
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The arachnoid sheath refers to a thin, delicate membrane that encapsulates the brain and spinal cord, serving as one of the three layers that make up the meninges, the protective covering of the central nervous system. The other two layers are the dura mater and the pia mater. The arachnoid sheath is located beneath the dura mater and above the pia mater.
This sheath is characterized by its spiderweb-like appearance, composed of fine, web-like filaments that extend from its surface, hence its name "arachnoid." The sheath functions to protect and cushion the brain and spinal cord, acting as a barrier against external mechanical forces.
One of the significant roles of the arachnoid sheath is to contain and circulate cerebrospinal fluid (CSF), a clear and colorless fluid that surrounds the brain and spinal cord. The sheath contains numerous blood vessels and extensions, known as arachnoid trabeculae, which help in the absorption and reabsorption of CSF.
Pathological conditions such as inflammation or infection can affect the arachnoid sheath, leading to conditions like arachnoiditis, a disorder characterized by inflammation of the sheath. This can result in symptoms such as chronic pain, numbness, tingling, and bladder and bowel disturbances. Additionally, arachnoid cysts, which are fluid-filled sacs that form within the meninges, can also occur within the arachnoid sheath.
In summary, the arachnoid sheath acts as a protective layer around the brain and spinal cord, working in conjunction with the other meninges to safeguard these vital structures from mechanical damage and help maintain the circulation of cerebrospinal fluid.
Etymology of ARACHNOID SHEATH
The word "arachnoid sheath" is derived from the combination of two terms: "arachnoid" and "sheath".
1. Arachnoid: The term "arachnoid" is derived from the Greek word "aráchnē", which means spider. The arachnoid mater is one of the three layers of the meninges, which are the protective coverings of the brain and spinal cord. The arachnoid mater resembles a spider's web, hence the name "arachnoid".
2. Sheath: The word "sheath" has Old English and Germanic origins. It comes from the Old English word "scēath", which means a covering or a holder for a weapon. In the context of anatomy, a sheath refers to a covering or protective layer around a structure.
