16.7
Nervous Tissue: Glial Cells
Glia, or neuroglia, are vital support cells that assist neurons in their functions. The term "glia" originates from the Greek word for "glue," reflect…
Glial cells or neuroglia are non-neuronal cells in the nervous system that outnumber neurons. These include astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS, and satellite and Schwann cells in the PNS.
Astrocytes are star-shaped cells with cytoplasmic processes that contact neurons, capillaries, and the pia mater— the covering of the brain and spinal cord.
Astrocytes support neurons, help to form the blood-brain barrier, regulate the concentration of ions, such as K+, and recycle released neurotransmitters.
Oligodendrocytes have flat cytoplasmic processes that wrap around axons, producing myelin, which protects and electrically insulates axons.
Microglia are small phagocytic cells that remove dead cells and pathogens from the CNS.
Ependymal cells are cuboidal or columnar cells that line the CNS ventricles and central canal. They contribute to cerebrospinal fluid production and monitor its circulation.
In the PNS, satellite cells surround and support neuronal cell bodies and regulate their microenvironment. Schwann cells or neurolemmocytes either myelinate single peripheral axons or enclose several unmyelinated axons. They also participate in axon regeneration.
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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.