In fact, it is the menynx interposed between the dura mater, above, and the pia mater, below.
Thin and delicate, the arachnoid gives life, on the internal front (that is, the one that looks towards the pia mater), to a space, called the subarachnoid space, in which the cerebrospinal fluid is contained.
The arachnoid is made up of a fibrous connective tissue rich in collagen and elastin, and which also includes a component of flat cells, essential to make the arachnoid itself an impermeable structure to the passage of the cerebrospinal fluid.
Unlike the dura mater and similarly to the pia mater, the arachnoid is poorly vascularized and innervated.
With the support of the other two meninges, the arachnoid has the task of protecting the brain and spinal cord.
The arachnoid can be the subject of various medical conditions (eg meningitis) and diagnostic / therapeutic procedures (lumbar puncture and spinal anesthesia).
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