Continuation of the Nervous Tissue

‭CONTINUATION OF THE NERVOUS TISSUE.‬ ‭1)‬ ‭Oligodendrocytes:‬ -‭ ‬ ‭Cells are common in humans because nshadow proportional to the complexity of the CNS‬ ‭(therefore more important than in other species).‬ ‭-‬ ‭Morphologies:‬ -‭ ‬ ‭Smaller size than astrocyte with fewer and fewer extensions‬ ‭branched (fewer bifurcations) than those of astrocytes.‬ ‭-‬ ‭rounded cell bodies.‬ ‭-‬ ‭there is no GFAP (glial fibrillary acidic protein) = intermediate filaments of‬ ‭astrocytes.‬ ‭-‬ ‭Function :‬ ‭-‬ ‭metabolic role: assumed due to the proximity of cell bodies to those of‬ ‭neurons so we think there are exchanges of materials between the 2 types of cells.‬ ‭-‬ ‭role in the formation of the myelin sheath of a certain number of axons:‬ ‭-‬ ‭2 types of cells for the production of the myelin sheath:‬ ‭-‬ ‭CNS: oligodendrocyte.‬ ‭-‬ ‭SNP: Schwann cell.‬ ‭-‬ ‭The myelin of the CNS is different in composition from that of the PNS.‬ ‭-‬ ‭An oligodendrocyte can myelinate several axons: each extension constitutes the myelin‬ ‭sheath around an axon.‬ ‭-‬ ‭A Schwann cell only myelinated only one.‬ ‭-‬ ‭several types of oligodendrocytes:‬ ‭-‬ ‭Satellites: Close to the cell bodies of neurons therefore metabolic action‬ ‭especially in the gray substance.‬ ‭-‬ ‭Interfascicular:‬ ‭in‬ ‭the‬‭branch‬‭substance‬‭between‬‭the‬‭fibers‬‭longitudinally‬‭tangled‬‭along‬‭the‬ ‭fibers so they are the ones who have the action of manufacturing the sheath of myelin.‬ ‭2)‬ ‭Micro Gliocytes:polymorphic. (microglia cells)‬ -‭ ‬ ‭Small cells inferior to oligodendrocytes.‬ ‭-‬ ‭Numerous cells with elongated cell bodies and some irregular extensions and have‬ ‭numerous spines/small structures that protrude from the axis of the extension therefore bristling‬ ‭with numerous spicules.‬ ‭-‬ ‭Found in gray and white matter.‬ ‭-‬ ‭Despite their morphology, these are cells derived from macrophages which have‬ ‭as origin the hematopoietic stem cell and which exert in the nervous tissue functions of‬ ‭phagocytosis, engulfment and destruction although the morphology is different from that of a macro‬ ‭traditional phage.‬ ‭-‬ ‭Some precursors of oligodendrocytes and astrocytes therefore intermediate between the‬ ‭spongioblast and the mature cell but most micro gliocytes are specific macrophages.‬ ‭3)‬ ‭Ependymocytes:‬ -‭ ‬ ‭Cells that line the cavities that are hollowed out in the nervous tissue.‬ ‭-‬ ‭During embryology a neural tube is formed with a lumen and a wall around it. This tube‬ ‭transforms to give the CNS but the lumen persists which will become the cavities of the CNS and‬ ‭the wall which is the nervous tissue: white matter and gray matter. This light is lined with an‬ ‭epithelium which is made by ependymocytes.‬ ‭-‬ ‭Elongated cylindrical cells juxtaposed to each other therefore in the form of an epithelium‬ a‭ lthough cIt is not a type of cell of epithelial origin. Those are cells linked to each other by junction‬ ‭systems (tight and others).‬ ‭-‬ ‭Apical pole: in the light therefore bathed in the liquid contained in these cavities: cephalic‬ ‭fluido spinal which circulates in the cavities, passes from the central cavities to the ependymal‬ ‭canal. There is therefore a separation between the CSF and the nervous tissue via these ependymal‬ ‭cells. The apical pole is provided with vibrating cilia and stereocilia (= a sort of large microvilli‬ ‭more or less agglutinated to one another).‬ ‭-‬ ‭Interior of the cell: no particularity except that very active cells.‬ ‭-‬ ‭Basal pole:Expansions that entangle with each other and form a densification ore which is‬ ‭one more element to isolate the CSF from the nervous tissue.‬