HISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLSHISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLS

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

astrocytesastrocytesoligodendrocytesoligodendrocytesmicroglial cellsmicroglial cells

• 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

NERVE FIBERS: MYELINATED AXONSNERVE FIBERS: MYELINATED AXONS

Longitudinal sectionLongitudinal section Cross-sectionCross-section

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Node of RanvierNode of Ranvier

Red arrow: outer mesaxonRed arrow: outer mesaxonBlue arrow: inner mesaxonBlue arrow: inner mesaxonSmall red arrow: neuro-Small red arrow: neuro-

filamentfilamentSmall blue arrow: micro-Small blue arrow: micro-

tubulustubulus

NERVE FIBERS: NON-MYELINATED AXONSNERVE FIBERS: NON-MYELINATED AXONS

Schwann cell nucleusSchwann cell nucleus

MesaxonMesaxon

Cross-section of the axonCross-section of the axon

Structure of a peripheral nerveStructure of a peripheral nerve

1-6. Layers of epineurium1-6. Layers of epineurium 7. Myelinated fiber with Schwann cell7. Myelinated fiber with Schwann cell 8. Non-myelinated fibers in a Schwann 8. Non-myelinated fibers in a Schwann cellcell 9. Capillary9. Capillary10-11. Endoneurium 10-11. Endoneurium 12. Perineurium12. Perineurium 13. Fibrocyte13. Fibrocyte