Changes

==Introduction==

==Introduction==

[[Image:neurondiagram.jpg|thumb|right|600px|Diagram of a neuron. LadyofHats, '''Wikimedia Commons''', 2007]]

[[Image:neurondiagram.jpg|thumb|right|600px|Diagram of a neuron. LadyofHats, '''Wikimedia Commons''', 2007]]

Nerves allow electrical impulses to propagate along their elongated cell extensions and facilitate the transfer of information throughout the body. Neural tissue is found within the [[Nervous and Special Senses - Anatomy & Physiology#Central Nervous System (CNS)|central nervous system (CNS)]] and the [[PNS Structure - Anatomy & Physiology|peripheral nervous system (PNS)]] and the composition and constituent parts of neurones and their surrounding cells differ only slightly.  

Nerves allow electrical impulses to propagate along their elongated cell extensions and facilitate the transfer of information throughout the body. Neural tissue is found within the [[Nervous and Special Senses - Anatomy & Physiology#Central Nervous System (CNS)|central nervous system (CNS)]] and the [[PNS Structure - Anatomy & Physiology|peripheral nervous system (PNS)]] and the composition and constituent parts of neurones and their surrounding cells differ only slightly.  

===Oligodendrocytes===

===Oligodendrocytes===

[[Image:oligodendrocyte.jpg|thumb|right|100px|Oligodendrocyte]]

[[Image:oligodendrocyte.jpg|thumb|right|250px|Oligodendrocyte]]

The term "oligodendrocyte" literally means a "cell with many branches". Oligodendrocyte precursors are found throughout the CNS and these precursors are post-mitotic, meaning oligodendrocytes can be replaced. Oligodendrocytes can [[PNS Structure - Anatomy & Physiology#The Process of Myelination|myelinate]] up to 40 axons at a time. The myelin sheath formed by oligodendrocytes has numerous functions including; decreasing any ion leakage from the axon lowering the capacitance of the cell membrane and increasing impulse speed along the axon by allowing saltatory conduction of action potentials between the nodes of Ranvier.

The term "oligodendrocyte" literally means a "cell with many branches". Oligodendrocyte precursors are found throughout the CNS and these precursors are post-mitotic, meaning oligodendrocytes can be replaced. Oligodendrocytes can [[PNS Structure - Anatomy & Physiology#The Process of Myelination|myelinate]] up to 40 axons at a time. The myelin sheath formed by oligodendrocytes has numerous functions including; decreasing any ion leakage from the axon lowering the capacitance of the cell membrane and increasing impulse speed along the axon by allowing saltatory conduction of action potentials between the nodes of Ranvier.

==Astrocytes==

==Astrocytes==

Astrocytes, or astroglia, are star-shaped glial cells within the brain which have many processes that envelope synapses made between neurons. Astrocytes have several functions including the biochemical support of the endothelial cells in forming the blood-brain barrier, provision of nutrients to nervous tissues and to form scar tissue during repair of the brain. The fluorescent image of astrocytes on the right is possible because astrocytes express glial fibrillary acidic protein (GFAP) which facilitates their identification. The following paragraphs provide a more detailed overview of the many functions of the astrocyte within the brain.

Astrocytes, or astroglia, are star-shaped glial cells within the brain which have many processes that envelope synapses made between neurons. Astrocytes have several functions including the biochemical support of the endothelial cells in forming the blood-brain barrier, provision of nutrients to nervous tissues and to form scar tissue during repair of the brain. The fluorescent image of astrocytes on the right is possible because astrocytes express glial fibrillary acidic protein (GFAP) which facilitates their identification. The following paragraphs provide a more detailed overview of the many functions of the astrocyte within the brain.

[[Image:astrocyte.jpg|thumb|right|150px|Astrocyte (immunofluorescence staining). Image courtesy of Alliance Européenne Dana pour le Cerveau (EDAB)]]

[[Image:astrocyte.jpg|thumb|right|250px|Astrocyte (immunofluorescence staining). Image courtesy of Alliance Européenne Dana pour le Cerveau (EDAB)]]

Another key role of astrocytes within the brain where they play an important structural role as well as performing the roles described above. Astrocytes are involved in the physical structuring of the brain and the interplay between astrocytes and mesenchymal cells is important in sculpting [[Forebrain_-_Anatomy_%26_Physiology#Cerebral_Cortex|sulci]] in development. Astrocytes also delineate the  CNS from the PNS by creating the CNS-PNS interface. The cells cover the surface of the brain and where this occurs the astrocytes' surface is coated by a basal lamina.

Another key role of astrocytes within the brain where they play an important structural role as well as performing the roles described above. Astrocytes are involved in the physical structuring of the brain and the interplay between astrocytes and mesenchymal cells is important in sculpting [[Forebrain_-_Anatomy_%26_Physiology#Cerebral_Cortex|sulci]] in development. Astrocytes also delineate the  CNS from the PNS by creating the CNS-PNS interface. The cells cover the surface of the brain and where this occurs the astrocytes' surface is coated by a basal lamina.

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==Microglial Cells==

==Microglial Cells==

[[Image:microglia.jpg|thumb|right|150px|Microglia]]

[[Image:microglia.jpg|thumb|right|250px|Microglia]]

Microglia are the CNS version of a mononuclear phagocyte system as the normal phagocytic white blood cells are unable to cross the blood-brain barrier. Microglial cells are derived from [[Bone Marrow - Anatomy & Physiology|bone marrow]] and are first seen in the brain just prior to the vascularistion stage of brain development. There are two populations of microglial cells; extrinsic cells which are located perivascularly and in the meninges, and intrinsic cells which are located within the substance of the neural tissue.

Microglia are the CNS version of a mononuclear phagocyte system as the normal phagocytic white blood cells are unable to cross the blood-brain barrier. Microglial cells are derived from [[Bone Marrow - Anatomy & Physiology|bone marrow]] and are first seen in the brain just prior to the vascularistion stage of brain development. There are two populations of microglial cells; extrinsic cells which are located perivascularly and in the meninges, and intrinsic cells which are located within the substance of the neural tissue.

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==Ependymal Cells==

==Ependymal Cells==

[[Image:Forkingaqueduct.jpg|thumb|right|150px|Forking aqueduct, showing ependymal cells. Image courtesy of BioMed Archive]]

[[Image:Forkingaqueduct.jpg|thumb|right|250px|Forking aqueduct, showing ependymal cells. Image courtesy of BioMed Archive]]

Ependymal cells make up the epithelial membrane which is the lining of the ventricular system within the brain and spinal cord. Ependymal cells are are involved in the production of [[Cerebral_Spinal_Fluid_-_Anatomy_%26_Physiology|cerebrospinal fluid]]. The cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord, and form part of the [[Cerebral_Spinal_Fluid_-_Anatomy_%26_Physiology|choroid plexus]]. The apical surfaces of ependymal cells are covered with

Ependymal cells make up the epithelial membrane which is the lining of the ventricular system within the brain and spinal cord. Ependymal cells are are involved in the production of [[Cerebral_Spinal_Fluid_-_Anatomy_%26_Physiology|cerebrospinal fluid]]. The cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord, and form part of the [[Cerebral_Spinal_Fluid_-_Anatomy_%26_Physiology|choroid plexus]]. The apical surfaces of ependymal cells are covered with

a layer of cilia and microvilli.

a layer of cilia and microvilli.