Oligodendrocyte
Encyclopedia
Oligodendrocytes or oligodendroglia (Greek, few tree glue), are a type of 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,...

 cell. They are a variety of neuroglia. Their main function is the insulation of axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s (the long projection of nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

 cells) in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 (the brain 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...

) of some vertebrates. (The same function is performed by Schwann cell
Schwann cell
Schwann cells or neurolemmocytes are the principal glia of the peripheral nervous system . Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle...

s in the peripheral nervous system
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

). A single oligodendrocyte can extend its processes to 50 axons, wrapping around approximately 1 μm of myelin sheath around each axon; Schwann cells, on the other hand, can wrap around only 1 axon.

Origin

Oligodendroglia arise during development from oligodendrocyte precursor cell
Oligodendrocyte precursor cell
Oligodendrocyte precursor cells in nervous tissue cells precede oligodendrocytes, and may also be able to generate neurons and astrocytes. The principal function of oligodendrocytes is to provide support to axons and to produce the Myelin sheath, which insulates and lowers the effective...

s, which can be identified by their expression of a number of antigens, including the ganglioside
Ganglioside
Ganglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...

 GD3, the NG2 chondroitin sulfate proteoglycan
Chondroitin sulfate
Chondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...

, and the platelet-derived growth factor-alpha receptor subunit PDGF-alphaR. In the rat forebrain, the majority of oligodendroglial progenitors arise during late embryogenesis and early postnatal development from cells of the subventricular zone
Subventricular zone
The subventricular zone is a paired brain structure situated throughout the lateral walls of the lateral ventricles. It has been associated with having four distinct layers of variable thickness and cell density, as well as cellular composition....

s (SVZ) of the lateral 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...

. SVZ
Subventricular zone
The subventricular zone is a paired brain structure situated throughout the lateral walls of the lateral ventricles. It has been associated with having four distinct layers of variable thickness and cell density, as well as cellular composition....

 cells migrate away from germinal
Germinal
Germinal is the thirteenth novel in Émile Zola's twenty-volume series Les Rougon-Macquart. Often considered Zola's masterpiece and one of the most significant novels in the French tradition, the novel – an uncompromisingly harsh and realistic story of a coalminers' strike in northern France...

zones to populate both developing white and gray matter, where they differentiate and mature into myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...

-forming oligodendroglia. However, it is not clear whether all oligodendroglial progenitors undergo this sequence of events. It has been suggested that some undergo apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

  and others fail to differentiate into mature oligodendroglia but persist as adult oligodendroglial progenitors.

Function

As part of the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

, oligodendrocytes are closely related to nerve cells, and, like all other 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, oligodendrocytes provide a supporting role for neurons. In addition, the nervous system of mammals depends crucially on myelin sheaths, which reduce ion leakage and decrease the capacitance of the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

. Myelin also increases impulse speed, as saltatory propagation
Saltatory conduction
Saltatory conduction is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials without needing to increase the diameter of an axon.-Mechanism:Because the cytoplasm of the axon is electrically...

 of action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

s occurs at the nodes of Ranvier
Nodes of Ranvier
Myelin sheath gaps or nodes of Ranvier are the gaps formed between the myelin sheaths generated by different cells. A myelin sheath is a many-layered coating, largely composed of a fatty substance called myelin, that wraps around the axon of a neuron and very efficiently insulates it...

 in between Schwann cells (of the PNS
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

) and oligodendrocytes (of the CNS
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

). Oligodendrocytes provide the same functionality as the insulation on a household electrical wire (with the rather large difference that, while household electrical wires are in a non-conducting medium - air - the axons run in a solution of water and ions, which conducts electrical current well). Furthermore, impulse speed of myelinated axons increases linearly with the axon diameter, whereas the impulse speed of unmyelinated cells increases only with the square root of the diameter. In contrast, Satellite oligodendrocytes are functionally distinct from most oligodendrocytes. They are not attached to neurons and, therefore, do not serve an insulating role. They remain apposed to neurons and regulate the extracellular fluid.

Pathology

Diseases that result in injury to the oligodendroglial cells include demyelinating diseases such as multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...

 and leukodystrophies
Leukodystrophy
Leukodystrophy refers to a group of disorders characterized by dysfunction of the white matter of the brain. The leukodystrophies are caused by imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers...

. Trauma to the body, e.g. spinal cord injury, can also cause demyelination. Cerebral palsy (periventricular leukomalacia) is caused by damage to developing oligodendrocytes in the brain areas around the cerebral ventricles. Spinal cord injury also causes damage to oligodendrocytes. In cerebral palsy, spinal cord injury, stroke and possibly multiple sclerosis, oligodendrocytes are thought to be damaged by excessive release of the neurotransmitter glutamate. Oligodendrocyte dysfunction may also be implicated in the pathophysiology of schizophrenia and bipolar disorder. Oligodendroglia are also susceptible to infection by the JC virus
JC virus
The JC virus or John Cunningham virus is a type of human polyomavirus and is genetically similar to BK virus and SV40. It was discovered in 1971 and named using the two initials of a patient with progressive multifocal leukoencephalopathy...

, which causes progressive multifocal leukoencephalopathy
Progressive multifocal leukoencephalopathy
Progressive multifocal leukoencephalopathy , also known as progressive multifocal leukoencephalitis, is a rare and usually fatal viral disease that is characterized by progressive damage or inflammation of the white matter of the brain at multiple locations .It occurs almost exclusively in...

 (PML), a condition that specifically affects white matter, typically in immunocompromised
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other...

 patients. Tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

s of oligodendroglia are called oligodendroglioma
Oligodendroglioma
Oligodendrogliomas are a type of glioma that are believed to originate from the oligodendrocytes of the brain or from a glial precursor cell. They occur primarily in adults but are also found in children...

s.

External links

  • The Department of Neuroscience at Wikiversity
  • NIF Search - Oligodendrocyte via the Neuroscience Information Framework
    Neuroscience Information Framework
    The Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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