Astrocyte

From Psychology Wiki

Community portal · Tasks to do · News · Help

Clinical · Educational · Ind&Org · Other fields · Professional · Transpersonal · World

Assessment | Biopsychology | Comparative | Cognitive | Developmental | Language
Personality | Philosophy | Research Methods | Social | Statistics

Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology

---

Astrocyte
Astrocytes can be visualized in culture because, like other glia, they express glial fibrillary acidic protein.
Latin	'
Gray's	subject #
System
MeSH	A08.637.200
[[Image:|190px|center|]]

Astrocytes (also known collectively as astroglia) are characteristic star-shaped glial cells in the brain.

Contents 1 Description 2 Functions 3 Calcium waves 4 Classification 4.1 by Location 4.2 by Anatomical Classification 4.3 by Transporter/receptor classification 5 Pathology 6 References 7 External links

[edit] Description

Astrocytes are sub-type of the glial cells in the brain. They are also known as astrocytic glial cells. Star-shaped, their many arms span all around neurons. They outnumber the neurons ten to one.^[1] Astrocytes are classically identified histologically by their expression of glial fibrillary acidic protein (GFAP). 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.

[edit] Functions

• Structural. A commonly accepted function is to physically structure the brain.
• Metabolic support. A second function is to provide neurons with nutrients such as glucose.
• Blood-brain barrier. The astrocyte end-feet encircling endothelial cells form part of the blood-brain barrier.
• 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.
• Regulation of ion concentration in the extracellular space. Astrocytes express potassium channels at a high density. When neurons are active, they release potassium, increasing its extracellular concentration. Because astrocytes are so permeable to potassium, they rapidly clear its 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.
• 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 LIM, a regulatory protein that promotes the myelinating activity of oligodendrocytes. This suggest that astrocytes have an executive-coordinating role in the brain.^[4]

[edit] 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]

[edit] Classification

There are several different ways to classify astrocytes:

[edit] by Location

• Type I: Those astrocytes are in direct contact with blood capillaries through astrocytique pod. They are actively helping neuronal metabolism and glucose delivery.
• Type II: Type II astrocytes surrounds neurones and synaptic gap. This coverage varies from 1 to 100%.

[edit] by Anatomical Classification

• Protoplasmic: found in grey matter and have many branching processes whose end-feet envelop synapses
• Fibrous: found in white matter and have long thin unbranched processes whose end-feet envelop nodes of Ranvier^[8]

[edit] 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

[edit] Pathology

Astrocytomas are primary intracranial tumors derived from astrocytes cells of the brain.

[edit] References

1. ↑ http://www.sfn.org/index.cfm?pagename=brainBriefings_astrocytes
2. ↑ 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. PMID 14766975.
3. ↑ Parri R, Crunelli V (2003). An astrocyte bridge from synapse to blood flow.. Nat Neurosci 6 (1): 5-6. PMID 12494240.
4. ↑ 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. PMID 16543131.
5. ↑ 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. PMID 14585601.
6. ↑ Newman, J Neurosci. 2001 Apr 1;21(7):2215-23
7. ↑ 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. PMID 10900020.
8. ↑ Memorial University of Newfoundland - Anatomy at MUN nerve/neuron

[edit] External links

• UIUC Histology Subject 57

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	Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells	astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)	Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues	epineurium, perineurium, endoneurium, nerve fascicle, meninges

de:Astrozyt

fr:Astrocyte nl:Astrocyt pt:Astrócito sk:Astrocyt zh:星形膠質細胞

This page uses content from the English-language version of Wikipedia. The original article was at Astrocyte. The list of authors can be seen in the page history. As with Psychology Wiki, the text of Wikipedia is available under the GNU Free Documentation License.