HISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLS HISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLS euroglia comprise over 90 % of the cells of the nervous system. euroglia comprise over 90 % of the cells of the nervous system. lial cells are relatively small. lial cells are relatively small. heir function is heir function is to provide structural support to provide structural support form the CNS boundary form the CNS boundary ensheath and insulate axons ensheath and insulate axons maintain the ionic homeostasis of the extracellular spa maintain the ionic homeostasis of the extracellular spa phagocyte cell debris phagocyte cell debris produce scar tissue produce scar tissue sification of neuroglia: sification of neuroglia: in the central nervous system (CNS): in the central nervous system (CNS): ependyma ependyma astrocytes astrocytes oligodendrocytes oligodendrocytes microglial cells microglial cells in the peripheral nervous system (PNS): neurolemmocytes: Schwann ce in the peripheral nervous system (PNS): neurolemmocytes: Schwann ce satellite satellite
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HISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLS Neuroglia comprise over 90 % of the cells of the nervous system. Glial cells are relatively small. Their function.
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Neuroglia comprise over 90 % of the cells of the nervous system.Neuroglia comprise over 90 % of the cells of the nervous system.Glial cells are relatively small.Glial cells are relatively small.Their function isTheir function is to provide structural supportto provide structural support
form the CNS boundaryform the CNS boundaryensheath and insulate axonsensheath and insulate axonsmaintain the ionic homeostasis of the extracellular spacemaintain the ionic homeostasis of the extracellular spacephagocyte cell debrisphagocyte cell debrisproduce scar tissueproduce scar tissue
Classification of neuroglia:Classification of neuroglia:• in the central nervous system (CNS): in the central nervous system (CNS): ependymaependyma
• in the peripheral nervous system (PNS): neurolemmocytes: Schwann cellsin the peripheral nervous system (PNS): neurolemmocytes: Schwann cells satellite cellssatellite cells
Neuroglia of the CNS: ependymal cellsNeuroglia of the CNS: ependymal cells
Ependymal cells line Ependymal cells line ventricular cavities in the brain ventricular cavities in the brain and the central canal of the spinal cord.and the central canal of the spinal cord.
They are cuboidal or columnar cells tightly packed together.They are cuboidal or columnar cells tightly packed together.Their luminal surface is ciliated and microvilliated.Their luminal surface is ciliated and microvilliated.The cerebrospinal fluid is produced by modified ependymal cells The cerebrospinal fluid is produced by modified ependymal cells
(choroid plexus)(choroid plexus)
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Neuroglia of the CNS: astrocytesNeuroglia of the CNS: astrocytes
They have the largest nuclei among glial cells. They have the largest nuclei among glial cells.
They are stellate-shaped with numerous processes:They are stellate-shaped with numerous processes:• in the white matter: long slender processes: fibrous astrocytesin the white matter: long slender processes: fibrous astrocytes• in the gray matter: shorter branching processes: protoplasmic astrocytes.in the gray matter: shorter branching processes: protoplasmic astrocytes.They contain glial fibrillary acidic protein (GFAP) forming glial filaments.They contain glial fibrillary acidic protein (GFAP) forming glial filaments.
Astrocyte processes form expanding endfeets which adjoin into limitingAstrocyte processes form expanding endfeets which adjoin into limitingmembranes: membranes: • membrana limitans gliae superficialis (at the surface of CNS)membrana limitans gliae superficialis (at the surface of CNS)• membrana limitans gliae perivascularis (blood-brain barrier).membrana limitans gliae perivascularis (blood-brain barrier).
Astrocytes Astrocytes provide structural support, provide structural support, form diffusion barriers around synapses,form diffusion barriers around synapses,
take up extracellular potassium ionstake up extracellular potassium ionsare capable of phagocytosisare capable of phagocytosisproliferate to form a scar in the case of injuryproliferate to form a scar in the case of injury
Schematic drawing of a protoplasmicSchematic drawing of a protoplasmicastrocyte:astrocyte:1.1. NucleusNucleus2.2. Glial filamentsGlial filaments3.3. Not foundNot found4.4. CapillaryCapillary5.5. Endfeet of the astroglia around capillaryEndfeet of the astroglia around capillary6.6. Basal lamina of the capillary endotheliumBasal lamina of the capillary endothelium7.7. Endfeet around a synapseEndfeet around a synapse8.8. Presynaptic terminalPresynaptic terminal9.9. Spiny dendriteSpiny dendrite10.10. Myelinated axonMyelinated axon11.11. Initial segment of an axonInitial segment of an axon12.12. Axo-axonic synapseAxo-axonic synapse13.13. Axospinous synapseAxospinous synapse14.14. Dendritic spineDendritic spine
Neuroglia of the CNS: oligodendrocytesNeuroglia of the CNS: oligodendrocytes
They have small spherical nuclei in routinely stained sections.They have small spherical nuclei in routinely stained sections.Their processes are thin and difficult to visualize.Their processes are thin and difficult to visualize.Their function in the gray matter is perineuronal satellite-like, in whiteTheir function in the gray matter is perineuronal satellite-like, in whitematter they form the myelin sheaths around axons.matter they form the myelin sheaths around axons.
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1.1. OligodendrocyteOligodendrocyte2.2. Tapering process of oligodendrocyteTapering process of oligodendrocyte3.3. AxonAxon4.4. Myelin sheathMyelin sheath5.5. Synapse at node of RanvierSynapse at node of Ranvier6.6. Soma of a neuronSoma of a neuron7.7. Axon hillockAxon hillock8.8. Synaptic boutonsSynaptic boutons
Neuroglia of the CNS: microgliaNeuroglia of the CNS: microglia
Microglia are cells of mesodermal origin that invade the CNS Microglia are cells of mesodermal origin that invade the CNS when it is vascularized.when it is vascularized.They have antigen presenting and phagocytic abilities.They have antigen presenting and phagocytic abilities.They have small elongated chromophilic nuclei.They have small elongated chromophilic nuclei.
Other cell types in the CNS Other cell types in the CNS with phagocytotic activity:with phagocytotic activity:astrocytes,astrocytes,oligodendrocytes, oligodendrocytes, pericytes,pericytes,hematogenous macrophageshematogenous macrophages
Silver impregnation
Neuroglia of the PNS: neurolemmocytesNeuroglia of the PNS: neurolemmocytes
They are glial cells responsible for the myelination of peripheral axons They are glial cells responsible for the myelination of peripheral axons (Schwann cell), or encapsulate neuronal cell bodies as satellite cells.(Schwann cell), or encapsulate neuronal cell bodies as satellite cells.They provide a protected immediate environment for PNS neurons.They provide a protected immediate environment for PNS neurons.They can become phagocytic upon nerve damage.They can become phagocytic upon nerve damage.
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Schwann cells (arrows)Schwann cells (arrows)
Cross-section of a myelinated Cross-section of a myelinated peripheral axon at the level of peripheral axon at the level of a Schwann cell nucleusa Schwann cell nucleus
Satellite cells ( yellow arrow andSatellite cells ( yellow arrow andno. 3) around a pseudounipolarno. 3) around a pseudounipolarneuron from the spinal ganglionneuron from the spinal ganglion