16.7
神经组织：神经胶质细胞
神经胶质细胞是协助神经元发挥功能的重要支持细胞。 “胶质细胞”一词源自希腊语“胶水”，反映了它们将神经系统结合在一起的作用。 这些细胞可分为六种类型：四种在中枢神经系统（CNS）中，两种在周围神经系统（PNS）中。
CNS神经胶质细胞包括星形胶质细胞、少突胶质细胞、小胶质细胞和室管膜细胞。
星形胶质…
胶质细胞或神经胶质细胞是神经系统中非神经元的细胞，其数量超过神经元。这些细胞包括中枢神经系统（CNS）中的星形胶质细胞、少突胶质细胞、小胶质细胞和室管膜细胞，以及周围神经系统（PNS）中的卫星细胞和施万细胞。
星形胶质细胞是具有胞质突起的星形细胞，其突起与神经元、毛细血管以及脑和脊髓的被膜——软脑膜相接触。
星形胶质细胞为神经元提供支持，参与血脑屏障的形成，调节离子（如 K+）浓度，并回收释放的神经递质。
少突胶质细胞具有扁平的细胞质突起，可包裹轴突并产生髓鞘，从而保护轴突并实现电绝缘。
小胶质细胞是可吞噬的微小细胞，能够清除中枢神经系统中的死亡细胞和病原体。
室管膜细胞是立方形或柱状细胞，排列在中枢神经系统脑室和中央管的内表面。它们参与脑脊液的生成，并监测其循环过程。
在周围神经系统（PNS）中，卫星细胞包绕并支持神经元胞体，调节其微环境。施万细胞（Schwann cells）或称神经鞘细胞，可形成单个周围轴突的髓鞘，或包裹多个无髓鞘轴突，同时还参与轴突再生过程。
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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.