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Pia mater

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Pia mater
Latin '
Gray's subject #193 878
MeSH A08.186.566.731
The medulla spinalis and its membranes.



Pia mater is the thin, translucent, mesh-like meningeal envelope, spanning nearly the entire surface of the brain. It is absent only at the natural openings between the ventricles, the foramen of Majendie, and the foramina of Luschka. The pia firmly adheres to the surface of the brain and loosely connects to the arachnoid layer.[3] Because of this continuum, the layers are often referred to as the pia arachnoid or leptomeninges. A subarachnoid space exists between the arachnoid layer and the pia, into which the choroid plexus releases and maintains the cerebrospinal fluid (CSF). The subarachnoid space contains trabeculae, or fibrous filaments, that connect and bring stability to the two layers, allowing for the appropriate protection from and movement of the proteins, electrolytes, ions, and glucose contained within the CSF.[4]



Cranial pia materEdit



Spinal pia materEdit

The spinal pia mater closely follows the curves of the spinal cord. It encloses the surface of the medulla spinalis, or spinal cord, and is attached to it through a connection to the anterior fissure. The pia mater attaches to the dura mater through 21 pairs of denticulate ligaments that pass through the arachnoid mater and dura mater of the spinal cord. These denticular ligaments help to anchor the spinal cord and prevent side to side movement, providing stability.[7] The membrane in this area is much thicker than the cranial pia mater, due to the two-layer composition of the pia membrane. The outer layer, which is made up of mostly connective tissue, is responsible for this thickness. Between the two layers are spaces which exchange information with the subarachnoid cavity as well as blood vessels. At the point where the pia mater reaches the conus medullaris or medullary cone at the end of the spinal cord, the membrane extends as a thin filament called the filum terminale or terminal filum, contained within the lumbar cistern. This filament eventually blends with the dura mater and extends as far as the coccyx, or tailbone. It then fuses with the periosteum, a membrane found at the surface of all bones, and forms the coccygeal ligament. Here it is called the central ligament and assists with movements of the trunk of the body.[6]

The pia mater is a neural crest derivative.



CSF production and circulationEdit

Cerebrospinal fluid is circulated through the ventricles, cisterns, and subarachnoid space within the brain and spinal cord. About 150 mL of CSF is always in circulation, constantly being recycled through the daily production of nearly 500 mL of fluid. The CSF is primarily secreted by the choroid plexus, however about one-third of the CSF is secreted by pia mater and the other ependymal surfaces of the ventricles and arachnoidal membranes. The ependymal surface refers to the thin epithelial membrane lining the brain and spinal cord canal. The CSF travels from the ventricles and cerebellum through three foramen in the brain, emptying into the cerebrum, and ending its cycle in the venous blood. The pia spans every surface crevice of the brain besides the foramen to allow the circulation of CSF to continue.[9]

Perivascular spacesEdit



Pia mater see blood–brain barrier (BBB). The BBB is responsible for keeping the CSF and brain fluid separate from the blood, allowing limited sodium, chlorine, and potassium through, and absolutely no plasma proteins nor organic molecules. Nearby, the ventricles are lined with the ependyma membrane. The CSF is only kept separate through the pia mater. Due to the ependyma and pia mater’s high permeability, nearly anything entering the CSF is able to enter the brain interstitial fluid.[9] However, regulation of this permeability is achieved through the abundant amount of astrocyte foot processes which are responsible for connecting the capillaries and the pia mater in a way that helps limit the amount of free diffusion going into the CNS.[10] The permeability of the pia then serves to closely connect the interstitial brain fluid and the CSF and allow them to remain nearly homogenous in terms of composition.[9]

The function of the pia mater is more simply visualized through these ordinary occurrences. This last property is evident in cases of head injury. When the head comes into contact with another object, the brain is protected from the skull due to the similarity in density between these two fluids so that the brain does not simply smash through into the skull, but rather its movement is slowed and stopped by the viscous ability of this fluid. The contrast in permeability between the BBB and pia mater mentioned before is also useful in the application of medicine. Drugs that enter the blood stream can not penetrate and function in the brain, but instead must be administered into the cerebrospinal fluid.[9]

Spinal cord compressionEdit





Main article: Evolution





Research directions Edit

Research is constantly ongoing involving the pia mater. A group of hospitals in Madrid, Spain published an article in 2004 based on the ultrastructural findings in human spinal pia mater in relation to subarachnoid anesthesia. The group was researching whether or not fenestrations were present in the pia mater membrane, and the effect they have on the transfer of local anesthetics across the membrane. Based on their research, fenestrations were found at the thoracic-lumbar junction, the conus medullaris, and nerve root levels. Although proving the presence of fenestrations in certain regions involving the pia mater, the group concluded that they could not determine the significance behind these fenestrations. They speculated the fenestrations at the lumbar spinal level may in fact facilitate the movement of local anesthetics across the pia mater membrane, which could in turn affect the onset time and latency of a subarachnoid block. Although no officially conclusion was made, research is still being done to prove their speculation.[16]

Notes Edit

  2. Parsons, Thomas Meninges. McGraw-Hill Companies 2008. URL accessed on 25 March 2011.
  4. 4.0 4.1 Timmons, Martini (2006). Human Anatomy, San Francisco: Pearson/Benjamin Cummings.
  5. Polzin, Scott. "Meninges." Gale Encyclopedia of Neurological Disorders. 2005. 20 Feb. 2011<>. l
  6. 6.0 6.1 6.2 Gray, Henry (1918). Susan Standring Anatomy of the Human Body, 40, Lea and Febiger.
  8. Marieb, Elaine (2001). Human Anatomy & Physiology, 453, 455, San Francisco: Benjamin Cummings.
  9. 9.0 9.1 9.2 9.3 9.4 Guyton, Arthur (2011). Textbook of Medical Physiology, Philadelphia: Saunders/Elsevier.
  10. Berne, Robert (2008). Berne & Levy Physiology, Philadelphia: Saunders/Elsevier.
  11. Ozawa, Hiroshi (July 2004). Mechanical properties and function of the spinal pia mater. Journal of Neurosurgery 1 (1).
  12. Remahl, Sten, Angeria (25). Observations at the CNS–PNS Border of Ventral Roots Connected to a Neuroma. Frontiers in Neurology 1 (136).
  13. Encyclopaedia Britannica, additional text.
  14. Hoffman, Olaf, Weber (November 2009). Pathophysiology and Treatment of Bacterial Meningitis. Therapeutic Advances in Neurological Disorders 2 (6): 1–7.
  15. Tew, John Meningiomas. Mayfield Clinic. URL accessed on 23 March 2011.

Further readingEdit

Wikimedia Commons has media related to:
[[Commons: Category:Pia mater

| Pia mater

  • Ozawa, Hiroshi (July 2004). "Mechanical properties and function of the spinal pia mater". Journal of Neurosurgery 1 (1).
  • Tubbs R, Salter G, Grabb P, Oakes W (2001). The denticulate ligament: anatomy and functional significance.. J Neurosurg 94 (2 Suppl): 271–5.

Meninges of the brain and medulla spinalis



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