Pia mater
Encyclopedia
Pia mater often referred to as simply the pia, is the delicate innermost layer of the meninges
, the membranes surrounding the brain
and spinal cord
. The word finds its roots in Latin, meaning literally "tender mother." The other two meningeal membranes are the dura mater
and the arachnoid mater
. Pia mater is a thin fibrous tissue that is impermeable to fluid. This allows the pia mater to enclose cerebrospinal fluid
. By containing this fluid the pia mater works with the other meningeal layers to protect and cushion the brain. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space created between blood vessels and pia mater functions as a lymphatic system
for the brain. When the pia mater becomes irritated and inflamed the result is meningitis
.
, the foramen of Majendie and the foramina of Luschka. The pia is firmly adhered to the surface of the brain and loosely connected to the arachnoid layer. 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.
The thin membrane is composed of fibrous tissue, which is covered by a sheet of flat cells impermeable to fluid on its outer surface. A network of blood vessels
travels to the brain and spinal cord by interlacing through the pia membrane. These capillaries are responsible for nourishing the brain. This vascular membrane is held together by areolar tissue covered by mesothelial cells from the delicate strands of connective tissue called the arachnoid trabeculae
. In the perivascular spaces, the pia mater begins as mesothelial lining on the outer surface, but the cells then fade to be replaced by neuroglia elements.
Although the pia mater is primarily structurally similar throughout, it spans both the spinal cord’s neural tissue and runs down the fissures of the cerebral cortex
in the brain. It is often broken down into two categories, the Cranial Pia Mater (pia mater encephali) and the Spinal Pia Mater (pia mater spinalis).
s, which are glial cell
s responsible for many functions including maintenance of the Extracellular
space. The cranial pia mater joins with the ependyma
which lines the cerebral ventricles
to form choroid plexus
es that produce cerebrospinal fluid
. Together with the other meningeal layers, the function of the pia mater is to protect the central nervous system by containing the cerebrospinal fluid, which cushions the brain and spine.
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
, the membranes surrounding the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. The word finds its roots in Latin, meaning literally "tender mother." The other two meningeal membranes are the dura mater
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
and the arachnoid mater
Arachnoid mater
The arachnoid mater, literally from Latin "spider -like mother", is one of the three meninges, the membranes that cover the brain and spinal cord...
. Pia mater is a thin fibrous tissue that is impermeable to fluid. This allows the pia mater to enclose cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
. By containing this fluid the pia mater works with the other meningeal layers to protect and cushion the brain. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space created between blood vessels and pia mater functions as a lymphatic system
Lymphatic system
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
for the brain. When the pia mater becomes irritated and inflamed the result is meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
.
Structure
Pia mater is the thin, transluscent, mesh-like meningeal envelope, spanning nearly the entire surface of the brain. It is only absent at the natural openings between the ventriclesVentricular system
The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
, the foramen of Majendie and the foramina of Luschka. The pia is firmly adhered to the surface of the brain and loosely connected to the arachnoid layer. Because of this continuum the layers are often referred to as the pia arachnoid or leptomeninges
Leptomeninges
In medicine, leptomeninges is a term used to refer to the pia mater and arachnoid mater, two of the membranes that surround the brain and the spinal cord....
. A subarachnoid space
Subarachnoid space
In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater....
exists between the arachnoid layer and the pia, into which the choroid plexus
Choroid plexus
The choroid plexus is a structure in the ventricles of the brain where cerebrospinal fluid is produced...
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.
The thin membrane is composed of fibrous tissue, which is covered by a sheet of flat cells impermeable to fluid on its outer surface. A network of blood vessels
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
travels to the brain and spinal cord by interlacing through the pia membrane. These capillaries are responsible for nourishing the brain. This vascular membrane is held together by areolar tissue covered by mesothelial cells from the delicate strands of connective tissue called the arachnoid trabeculae
Arachnoid trabeculae
The arachnoid trabeculae are delicate strands of connective tissue that loosely connect the two innermost layers of the meninges -- the arachnoid mater and the pia mater. They are found within the subarachnoid space where cerebrospinal fluid is also found...
. In the perivascular spaces, the pia mater begins as mesothelial lining on the outer surface, but the cells then fade to be replaced by neuroglia elements.
Although the pia mater is primarily structurally similar throughout, it spans both the spinal cord’s neural tissue and runs down the fissures of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
in the brain. It is often broken down into two categories, the Cranial Pia Mater (pia mater encephali) and the Spinal Pia Mater (pia mater spinalis).
Cranial pia mater
The section of the pia mater enveloping the brain is known as the cranial pia mater. It is anchored to the brain by the processes of astrocyteAstrocyte
Astrocytes , also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord...
s, which are glial cell
Glial cell
Glial cells, sometimes called neuroglia or simply glia , are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the brain, and for neurons in other parts of the nervous system such as in the autonomous nervous system...
s responsible for many functions including maintenance of the Extracellular
Extracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...
space. The cranial pia mater joins with the ependyma
Ependyma
Ependyma is the thin epithelial membrane lining the ventricular system of the brain and the spinal cord. Ependyma is one of the four types of neuroglia in the central nervous system. It is involved in the production of cerebrospinal fluid ....
which lines the cerebral ventricles
Ventricular system
The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
to form choroid plexus
Choroid plexus
The choroid plexus is a structure in the ventricles of the brain where cerebrospinal fluid is produced...
es that produce cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
. Together with the other meningeal layers, the function of the pia mater is to protect the central nervous system by containing the cerebrospinal fluid, which cushions the brain and spine.
Further reading
- Martini, F. Timmons, M. and Tallitsch, R. Human Anatomy. 5th ed. San Francisco: Pearson/Benjamin Cummings, 2006.
- Saladin, Kenneth. Anatomy and Physiology- the Unity of Form and Function. 5th Ed. New York, NY: McGraw-Hill, 2010. 485. Print.
- Gray, Henry (1918). Susan Standring. ed. Anatomy of the Human Body (40 ed.). Lea and Febiger.
- Ozawa, Hiroshi (July 2004). "Mechanical properties and function of the spinal pia mater". Journal of Neurosurgery 1 (1).
- Clinically Oriented Anatomy. Moore, Keith and Arthur F. Dalley. Philadelphia, Lipincott, Williams and Williams 2006.