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Tecido Nervoso: Células Gliais
Glia, ou neuroglia, são células de suporte vitais que auxiliam os neurônios em suas funções. O termo "glia" origina-se da palavra grega para "cola", r…
As células gliais ou neuroglia são células não neuronais do sistema nervoso que superam os neurônios. Estes incluem astrócitos, oligodendrócitos, micróglia e células ependimárias no SNC e células satélites e de Schwann no SNP.
Os astrócitos são células em forma de estrela com processos citoplasmáticos que entram em contato com neurônios, capilares e a pia-máter - a cobertura do cérebro e da medula espinhal.
Os astrócitos sustentam os neurônios, ajudam a formar a barreira hematoencefálica, regulam a concentração de íons, como o K+, e reciclam os neurotransmissores liberados.
Os oligodendrócitos têm processos citoplasmáticos planos que envolvem os axônios, produzindo mielina, que protege e isola eletricamente os axônios.
Microglia são pequenas células fagocíticas que removem células mortas e patógenos do SNC.
As células ependimárias são células cuboidais ou colunares que revestem os ventrículos do SNC e o canal central. Eles contribuem para a produção de líquido cefalorraquidiano e monitoram sua circulação.
No SNP, as células satélites circundam e sustentam os corpos celulares neuronais e regulam seu microambiente. As células de Schwann ou neurolemmócitos mielinizam axônios periféricos únicos ou envolvem vários axônios não mielinizados. Eles também participam da regeneração do axônio.
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Q1: What are glial cells and how do they differ from neurons?
Glial cells, or neuroglia, are non-neuronal support cells that outnumber neurons in the nervous system. The term 'glia' comes from Greek meaning 'glue,' reflecting their role in holding the nervous system together. Unlike neurons, glial cells provide structural support, maintain chemical balance, and assist neurons in their functions rather than transmitting electrical signals.
Q2: What are the main types of glial cells in the central nervous system?
The CNS contains four main glial cell types: astrocytes are star-shaped cells that support neurons and form the blood-brain barrier; oligodendrocytes produce myelin sheaths around axons; microglia are phagocytic cells that remove debris and pathogens; and ependymal cells line the ventricles and produce cerebrospinal fluid.
Q3: How do astrocytes support neuronal function?
Astrocytes contact neurons, capillaries, and the pia mater with their cytoplasmic processes. They regulate ion concentrations like K+, recycle released neurotransmitters, help form the blood-brain barrier, and guide neuronal growth during embryonic development, maintaining the chemical environment neurons need to function properly.
Q4: What is the role of oligodendrocytes in the nervous system?
Oligodendrocytes produce and maintain myelin sheaths around CNS axons. Myelin is a multilayered lipid and protein covering that electrically insulates axons and protects them. Unlike Schwann cells in the PNS, a single oligodendrocyte can myelinate multiple axons, increasing efficiency of signal transmission.
Q5: What are the differences between Schwann cells and satellite cells in the PNS?
Schwann cells encircle axons and form myelin sheaths, with each Schwann cell myelinating only one axon. They also participate in axon regeneration. Satellite cells, by contrast, surround neuronal cell bodies in PNS ganglia, providing structural support and regulating material exchange between neurons and interstitial fluid.
Q6: How do microglia contribute to CNS health?
Microglia are small phagocytic cells that function as immune cells within the CNS. They actively remove dead cells, cellular debris, and pathogens from the nervous tissue, maintaining a clean environment essential for proper neuronal function and protecting the brain and spinal cord from infection.
Q7: What functions do ependymal cells perform in the CNS?
Ependymal cells are cuboidal or columnar cells arranged in a single layer that line the brain's ventricles and spinal cord's central canal. They produce cerebrospinal fluid, monitor its circulation, and form the blood-cerebrospinal fluid barrier, protecting the CNS from harmful substances while allowing nutrient delivery.