Sierra Acai Company
Sierra Acai Company
Open 7 Days a Week
MonaVie Independent Distributor
Distributor Training
Shop Online
Enroll Now
Buy Wholesale and maintain an Active status for 2 months and we will refund your $39 Distributor Fee
Friends
Buy Wholesale and maintain an Active status for 2 months and we will refund your $39 Distributor Fee
07-SEPTEMBER-2008 03:17:44 - Astrocyte Redirected from Astrocytes Astrocyte Astrocytes can be visualized in culture because, like other glia, they express glial fibrillary acidic protein. Precursor Glioblast MeSH Astrocytes Dorlands/Elsevier a_68/12165688 Astrocytes also known collectively as astroglia are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical support of endothelial cells which form the blood-brain barrier, the provision of nutrients to the nervous tissue, and a principal role in the repair and scarring process in the brain. Contents 1 Description 2 Functions 3 Calcium waves 4 Classification 4.1 by Lineage and antigenic phenotype 4.2 by Anatomical Classification 4.3 by Transporter/receptor classification 5 Bergmann glia 6 Pathology 7 References 8 External links Description Astrocytes are a sub-type of the glial cells in the brain and spinal cord. They are also known as astrocytic glial cells. Star-shaped, their many processes envelope synapses made by neurons. Astrocytes are classically identified histologically as many of these cells express the intermediate filament glial fibrillary acidic protein GFAP. Two forms of astrocytes exist in the CNS, fibrous and protoplasmic. The former is usually located within white matter, have relatively few organelles, and exhibit long unbranched organelles. This type often have vascular feet that physically connect the cells to the outside of capillary wall when they are in close proximity of them. The latter, found in grey matter tissue, possess a larger quantity of organelles, and exhibit short and highly branched cellular processes. The two forms of astrocytes when in proximity to the pia mater sends out process to form the pia-glial membrane. Astrocytes red amongst neurons in the living cerebral cortex Astrocytes red amongst neurons in the living cerebral cortex Previously in medical science, the neuronal network was considered the only important one, and astrocytes were looked upon as gap fillers. But recently they have been reconsidered, and are now thought to play a number of active roles in the brain, including the secretion or absorption of neural transmitters and maintenance of the blood-brain barrier. Functions Structural: involved in the physical structuring of the brain. Metabolic support: they provide neurons with nutrients such as glucose. Blood-brain barrier: the astrocyte end-feet encircling endothelial cells were thought to aid in the maintenance of the blood-brain barrier, but recent research indicates that they do not play a substantial role, instead it is the tight junctions and basal lamina of the cerebral endothelial cells that play the most substantial role in maintaining the barrier.citation needed Transmitter reuptake and release: astrocytes express plasma membrane transporters such as glutamate transporters for several neurotransmitters, including glutamate, ATP and GABA. More recently, astrocytes were shown to release glutamate or ATP in a vesicular, Ca2+-dependent manner.1 Regulation of ion concentration in the extracellular space: astrocytes express potassium channels at a high density. When neurons are active, they release potassium, increasing the local extracellular concentration. Because astrocytes are highly permeable to potassium, they rapidly clear the excess accumulation in the extracellular space. If this function is interfered with, the extracellular concentration of potassium will rise, leading to neuronal depolarization by the Goldman equation. Abnormal accumulation of extracellular potassium is well known to result in epileptic neuronal activity.citation needed Modulation of synaptic transmission: in the supraoptic nucleus of the hypothalamus, rapid changes in astrocyte morphology have been shown to affect heterosynaptic transmission between neurons.2 Vasomodulation: astrocytes may serve as intermediaries in neuronal regulation of blood flow.3 Promotion of the myelinating activity of oligodendrocytes: electrical activity in neurons causes them to release ATP, which serves as an important stimulus for myelin to form. Surprisingly, the ATP does not act directly on oligodendrocytes. Instead it causes astrocytes to secrete cytokine leukemia inhibitory factor LIF, a regulatory protein that promotes the myelinating activity of oligodendrocytes. This suggest that astrocytes have an executive-coordinating role in the brain.4 Nervous system repair: upon injury to nerve cells within the central nervous system, astrocytes become phagocytic to ingest the injured nerve cells. The astrocytes then fill up the space to form a glial scar, repairing the area and replacing the CNS cells that cannot regenerate.citation needed Recent studies have shown that astrocytes play an important function in the regulation of neural stem cells. Research from the Schepens Eye Research Institute at Harvard shows the human brain to abound in neural stem cells, which are kept in a dormant state by chemical signals ephrin-A2 and ephrin-A3 from the astrocytes. The astrocytes are able to activate the stem cells to transform into working neurons by dampening the release of ephrin-A2 and ephrin-A3.citation needed Furthermore, studies are underway to determine whether astroglia play an instrumental role in depression, based on the link between diabetes and depression. Altered CNS glucose metabolism is seen in both these conditions, and the astroglial cells are the only cells with insulin receptors in the brain. Calcium waves Astrocytes are linked by gap junctions, creating an electrically coupled syncytium.5 An increase in intracellular calcium concentration can propagate outwards through this syncytium. Mechanisms of calcium wave propagation include diffusion of IP3 through gap junctions and extracellular ATP signalling.6 Calcium elevations are the primary known axis of activation in astrocytes, and are necessary and sufficient for some types of astrocytic glutamate release.7 Classification There are several different ways to classify astrocytes: by Lineage and antigenic phenotype These have been established by classic work by Raff et al in early 1980s on Rat optic nerves. Type 1: Antigenically Ran2+, GFAP+, FGFR3+, A2B5- thus resembling the type 1 astrocyte of the postnatal day 7 rat optic nerve. These can arise from the tripotential glial restricted precursor cells GRP, but not from the bipotential O2A/OPC oligodendrocyte, type 2 astrocyte precursor, also called Oligodendrocye progenitor cell cells. Type 2: Antigenically A2B5+, GFAP+, FGFR3-, Ran 2-. These cells can develop in vitro from the either tripotential GRP probably via O2A stage or from bipotential O2A cells which some people think may in turn have been derived from the GRP or in vivo when the these progenitor cells are transplanted into lesion sites but probably not in normal development, at least not in the rat optic nerve. Type-2 astrocytes are the major astrocytic component in postnatal optic nerve cultures that are generated by O2A cells grown in the presence of fetal calf serum but are not thought to exist in vivo Fulton et al., 1992. by Anatomical Classification Protoplasmic: found in grey matter and have many branching processes whose end-feet envelop synapses. Some protoplasmic astrocytes are generated by multipotent subventricular zone progenitor cells.89 Fibrous: found in white matter and have long thin unbranched processes whose end-feet envelop nodes of Ranvier.10 Some fibrous astrocytes are generated by radial glia.1112131415 by Transporter/receptor classification GluT type: express glutamate transporters EAAT1/SLC1A3 and EAAT2/SLC1A2 and respond to synaptic release of glutamate by transporter currents GluR type: express glutamate receptors mostly mGluR and AMPA type and respond to synaptic release of glutamate by channel-mediated currents and IP3-dependent Ca2+ transients Bergmann glia SLC1A3 expression highlights Bergmann glia in the brain of a mouse at 7th postnatal day, sagittal section. SLC1A3 expression highlights Bergmann glia in the brain of a mouse at 7th postnatal day, sagittal section. Bergmann glia, a type of glia1617 also known as radial epithelial cells as named by Camillo Golgi, are astrocytes in the cerebellum that have their cell bodies in the Purkinje cell layer and processes that extend into the molecular layer, terminating with bulbous endfeet at the pial surface. Bergmann glia express high densities of glutamate transporters that limit diffusion of the neurotransmitter glutamate during its release from synaptic terminals. Besides their role in early development of the cerebellum, Bergmann glia are also required for the pruning or addition of synapses.citation needed Pathology Astrocytomas are primary intracranial tumors derived from astrocytes cells of the brain. References ^ Santello M, Volterra A 2008. Synaptic modulation by astrocytes via Ca2+-dependent glutamate release.. Neuroscience Mar 22. doi:10.1016/j.neuroscience.2008.03.039. PMID 18455880. ^ Piet R, Vargová L, Syková E, Poulain D, Oliet S 2004. Physiological contribution of the astrocytic environment of neurons to intersynaptic crosstalk. Proc Natl Acad Sci U S A 101 7: 2151-5. doi:10.1073/pnas.0308408100. PMID 14766975. ^ Parri R, Crunelli V 2003. An astrocyte bridge from synapse to blood flow. Nat Neurosci 6 1: 5-6. doi:10.1038/nn0103-5. PMID 12494240. ^ Ishibashi T, Dakin K, Stevens B, Lee P, Kozlov S, Stewart C, Fields R 2006. Astrocytes promote myelination in response to electrical impulses. Neuron 49 6: 823-32. doi:10.1016/j.neuron.2006.02.006. PMID 16543131. ^ Bennett M, Contreras J, Bukauskas F, Sáez J 2003. New roles for astrocytes: gap junction hemichannels have something to communicate. Trends Neurosci 26 11: 610-7. doi:10.1016/j.tins.2003.09.008. PMID 14585601. ^ Newman, J Neurosci. 2001 Apr 1;217:2215-23 ^ Parpura V, Haydon P 2000. Physiological astrocytic calcium levels stimulate glutamate release to modulate adjacent neurons. Proc Natl Acad Sci U S A 97 15: 8629-34. doi:10.1073/pnas.97.15.8629. PMID 10900020. ^ Levison SW, Goldman JE February 1993. Both oligodendrocytes and astrocytes develop from progenitors in the subventricular zone of postnatal rat forebrain. Neuron 10 2: 201-12. PMID 8439409. ^ Zerlin M, Levison SW, Goldman JE November 1995. Early patterns of migration, morphogenesis, and intermediate filament expression of subventricular zone cells in the postnatal rat forebrain. J. Neurosci. 15 11: 7238-49. PMID 7472478. ^ Anatomy at MUN nerve/neuron ^ Choi BH, Lapham LW June 1978. Radial glia in the human fetal cerebrum: a combined Golgi, immunofluorescent and electron microscopic study. Brain Res. 148 2: 295-311. PMID 77708. ^ Schmechel DE, Rakic P June 1979. A Golgi study of radial glial cells in developing monkey telencephalon: morphogenesis and transformation into astrocytes. Anat. Embryol. 156 2: 115-52. PMID 111580. ^ Misson JP, Edwards MA, Yamamoto M, Caviness VS November 1988. Identification of radial glial cells within the developing murine central nervous system: studies based upon a new immunohistochemical marker. Brain Res. Dev. Brain Res. 44 1: 95-108. PMID 3069243. ^ Voigt T November 1989. Development of glial cells in the cerebral wall of ferrets: direct tracing of their transformation from radial glia into astrocytes. J. Comp. Neurol. 289 1: 74-88. doi:10.1002/cne.902890106. PMID 2808761. ^ Goldman SA, Zukhar A, Barami K, Mikawa T, Niedzwiecki D August 1996. Ependymal/subependymal zone cells of postnatal and adult songbird brain generate both neurons and nonneuronal siblings in vitro and in vivo. J. Neurobiol. 30 4: 505-20. doi:10.1002/SICI1097-469519960830:4505::AID-NEU63.0.CO;2-7. PMID 8844514. ^ Riquelme R, Miralles C, De Blas A 2002. Bergmann glia GABAA receptors concentrate on the glial processes that wrap inhibitory synapses. J. Neurosci. 22 24: 10720-30. PMID 12486165. ^ Yamada K, Watanabe M 2002. Cytodifferentiation of Bergmann glia and its relationship with Purkinje cells. Anatomical science international / Japanese Association of Anatomists 77 2: 94-108. PMID 12418089. External links UIUC Histology Subject 57 Astrocytes at Society for Neuroscience v d e Histology: nervous tissue Neurons gray matter soma - axon axon hillock, axoplasm, axolemma, neurofibril/neurofilament dendrite Nissl body, dendritic spine, apical dendrite, basal dendrite types: bipolar - pseudounipolar - multipolar - pyramidal - Purkinje - granule Afferent nerve/Sensory nerve/Sensory neuron GSA - GVA - SSA - SVA - fibers Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain Efferent nerve/Motor nerve/Motor neuron GSE - GVE - SVE - Upper motor neuron - Lower motor neuron α motorneuron, γ motorneuron Synapses neuropil - synaptic vesicle - neuromuscular junction - electrical synapse - Interneuron Renshaw Sensory receptors Meissner's corpuscle - Merkel nerve ending - Pacinian corpuscle - Ruffini ending - Muscle spindle - Free nerve ending - Olfactory receptor neuron - Photoreceptor cell - Hair cell - Taste bud Glial cells Astrocyte Radial glia - Oligodendrocyte - Ependymal cells Tanycytes - Microglia Myelination white matter CNS: Oligodendrocyte PNS: Schwann cell - Neurolemma - Nodes of Ranvier/Internode - Schmidt-Lanterman incisures Related connective tissues epineurium - perineurium - endoneurium - nerve fascicle - meninges Retrieved from http://en..org/wiki/Astrocyte Categories: Nervous system | Glial cells | Human cellsHidden categories: All articles with statements | Articles with statements since January 2008 | Articles with statements since June 2008 Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages БългарÑ?ки Català Deutsch Español Français עברית Italiano Lietuvių Nederlands 日本語 Polski Português РуÑ?Ñ?кий SlovenÄ?ina SlovenÅ¡Ä?ina СрпÑ?ки / Srpski ä¸æ–‡ This page was last modified on 9 August 2008, at 13:49
39 Reasons to Drink Acai Juice Every Day
What is MonaVie - Watch the 8-minute video
Discovering MonaVie Video
The Power of You Video
Effects of MonaVie Active on Antioxidant Capacity in Humans
Log into your Wholesale MonaVie Account
So many of us do not eat a balanced diet, get enough sleep, have too much stress, or are impacted with toxins and pollutants. Drinking 2 ounces of MonaVie twice a day will help your body detoxify as well as build your immune system. Its the smartest thing you can do for yourself, so start today. Buying MonaVie through our company guarantees you support 7 days a week and, if you would like to share MonaVie with your family and friends we will guide you from start to finish.
1. Click on Enroll Now (30 - 55% off retail price)
2. Pay $39 for your Wholesale ID number.
3. NO minimum order required.
4. MonaVie is delivered to your door in 3 to 5 days.