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The Meninges

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As we learned about in the blog post about the Brain Box, the brain is protected by the skull, meninges, and cerebrospinal fluid (CSF). The meninges, which sit below the skull and vertebral column, is a series of three membranes that surround the brain and spinal cord. Its function is to protect and support the brain and spinal cord and contain cerebrospinal fluid (CSF).

Image result for the meninges
The three layers of the meninges (from outermost to innermost) are the dura mater, arachnoid mater and pia mater. The dura mater is a thick, tough layer that adheres to the skull on one side and the arachnoid mater on the other. It is an extra protective layer that attaches the brain to the skull and the spinal cord to the vertebral column.

Beneath the dura mater is the arachnoid mater. The arachnoid mater is named after its appearance that resembles a cobweb. It is made of strands of connective tissue, known as arachnoid trabeculae, that suspend the brain in place. Between the arachnoid mater and the underlying pia mater is the subarachnoid space, which contains CSF. The subarachnoid space is connected to the fourth ventricle of the brain.

Beneath the arachnoid mater is the pia mater. The pia mater is a thin, tight membrane that closely adheres to the brain. It helps to contain cerebrospinal fluid, as the subarachnoid space is directly above it.

The space between the dura mater of the spinal cord and the vertebral column is known as the epidural space. Anesthesia is often administered here.

The lumbar cistern is a CSF-filled cavity where the dura and arachnoid mater extend beyond the end of the spinal cord. There is no spinal cord present in the lumbar cistern, so a CSF cavity is created. Therefore, CSF can be withdrawn from the lumbar cistern; a needle can be inserted here without the risk of damaging the spinal cord. This procedure of CSF withdrawal is known as a lumbar puncture or a spinal tap. A spinal tap is used to diagnose meningitis (inflammation of the meninges).
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 Image Credit: 
(1) “Layers of the Meninges.” Wikimedia Commons, upload.wikimedia.org/wikipedia/commons/4/48/Illu_meninges.jpg.
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