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Tissu nerveux : cellules gliales
Les cellules gliales, ou névroglie, sont des cellules de soutien vitales qui assistent les neurones dans leurs fonctions. Le terme « gliale » vient du…
Les cellules gliales ou neuroglies sont des cellules non neuronales du système nerveux qui sont plus nombreuses que les neurones. Il s’agit notamment des astrocytes, des oligodendrocytes, des cellules microgliales et épendymaires dans le SNC, ainsi que des cellules satellites et Schwann dans le SNP.
Les astrocytes sont des cellules en forme d’étoile avec des processus cytoplasmiques qui entrent en contact avec les neurones, les capillaires et la pie-mère, c’est-à-dire le revêtement du cerveau et de la moelle épinière.
Les astrocytes soutiennent les neurones, aident à former la barrière hémato-encéphalique, régulent la concentration d’ions, tels que K+, et recyclent les neurotransmetteurs libérés.
Les oligodendrocytes ont des processus cytoplasmiques plats qui s’enroulent autour des axones, produisant de la myéline, qui protège et isole électriquement les axones.
Les microglies sont de petites cellules phagocytaires qui éliminent les cellules mortes et les agents pathogènes du SNC.
Les cellules épendymaires sont des cellules cuboïdes ou cylindriques qui tapissent les ventricules et le canal central du SNC. Ils contribuent à la production de liquide céphalo-rachidien et surveillent sa circulation.
Dans le SNP, les cellules satellites entourent et soutiennent les corps cellulaires neuronaux et régulent leur microenvironnement. Les cellules de Schwann ou neurolemmocytes myélinisent des axones périphériques uniques ou renferment plusieurs axones non myélinisés. Ils participent également à la régénération axonale.
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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.