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Microglia are a type of glial cell located throughout the brain and spinal cord of the central nervous system (CNS). [1] Microglia account for about 10–15% of cells found within the brain. [2] As the resident macrophage cells, they act as the first and main form of active immune defense in the CNS. [3]
In general, neuroglial cells are smaller than neurons. There are approximately 85 billion glia cells in the human brain, [8] about the same number as neurons. [8] Glial cells make up about half the total volume of the brain and spinal cord. [27] The glia to neuron-ratio varies from one part of the brain to another.
Brain cells make up the functional tissue of the brain. The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges , blood vessels , and ducts. The two main types of cells in the brain are neurons , also known as nerve cells, and glial cells , also known as neuroglia. [ 1 ]
Oligodendrocytes are a type of glial cell, non-neuronal cells in the central nervous system.They arise during development from oligodendrocyte precursor cells (OPCs), [8] which can be identified by their expression of a number of antigens, including the ganglioside GD3, [9] [10] [11] the NG2 chondroitin sulfate proteoglycan, and the platelet-derived growth factor-alpha receptor subunit (PDGF ...
While the cells that remain as the neural tube form the brain and spinal cord, the other cells that were part of the neural plate migrate away from the tube as neural crest cells. After an epithelial–mesenchymal transition , these cells form the autonomic nervous system and certain cells of the peripheral nervous system .
[1]: 132 Similar in physiology and connectivity to W cells in cat LGN, K cells form three pairs of layers in macaques. The middle pair (K3 and K4) relays input from short-wavelength cones to the cytochrome-oxidase blobs of primary visual cortex (V1). The dorsal-most pair (K5 and K6) relays low-acuity visual information to layer I of V1.
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In the central nervous system (brain, spinal cord and optic nerves), myelination is formed by specialized glial cells called oligodendrocytes, each of which sends out processes (limb-like extensions from the cell body) to myelinate multiple nearby axons; while in the peripheral nervous system, myelin is formed by Schwann cells (neurolemmocytes ...