HISTOLOGY OF NERVOUS SYSTEMdr. I Wayan Sugiritama,M.KesHISTOLOGY DEPARTMENTMEDICAL FACULTY OF UDAYANA UNIVERSITY

CONTENTSCells of nervous systemSynaptic communicationCNS and PNS and its associated structureRegeneration of nervous system**

CELLS OF NERVOUS SYSTEM**NEURONNEUROGLIA

STRUCTURE OF NEURONPrinciple cells of Nervous TissueConsist of 3 parts :CELL BODY (perikaryon/soma)A single AXONMultiple DENDRITES 5-150 m

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CELL BODY (PERIKARYON)Central portion of the cellGenerally are polygonalDifferent shape and size characteristic regions of nervous systemContain :NucleusPerinuclear cytoplasm**

ULTRASTRUCTURE OF NEURONNucleus : large, spherical to ovoid and centraly locateda single prominent nucleolus finely dispersed chromatin trancriptionaly active **

ULTRASTRUCTURE OF NEURONCytoplasm :Abundant of R.E.RPolyribosomes Basic dyes (a+b) Nissl Bodies lots of S.E.R.Golgi bodies

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ULTRASTRUCTURE OF NEURONCytoplasm Many mitochondria, most abundant in axon terminalextensive cytoskeleton axonal transportOne centriole do not undergo cell divisions**

DENDRITE AND AXONAXONSingle process up to 100 cm Originate from axon hillockDevoid ribosomeDilatation of distal portion end bulbs synapseconducting impulse away from the somaAxonal transportDENDRITESMultiple elongated processesCytoplasmic~perikaryon (devoid golgi complex)Receiving stimuli **

NEURONS CLASSIFICATION :According to the size and shape of the processes (Dorsal root & cranial nerve ganglia) (Pyramidal & purkinje)**

NEURONS CLASSIFICATION :**

NEURON ORGANIZATIONCORTEXNeuron form six layers on the cerrebrumForm three layers on the cerrebellumNUCLEIIn subcortical region (thalamus, midbrain, brainstem and spinal cord) neuron form irregular cluster nucleiGANGLIONCluster of neuron outside the CNS**

SYNAPSESSites of impulse transmissionConvert electrical signal into chemical signalPermit neurons to communicate

Types of synapses :Axodentritic synapseAxosomatic synapseAxoaxonic synapse**

SYNAPS**

NEUROGLIAL CELLSMetabolic and mechanical support for neuron10 times abundant than neuronsNeuroglial cells undergo mitosisClassification :OligodendrocytesAstrocytesEpendymal CellsMicrogliaSchwan cells

CNSPNS**

NEUROGLIAL CELLSAstrocytesPedicles binds to capillaries and to the pia mater form glial limitansControlling the ionic & chemical environment of neuronsEnergy metabolismForm cellular scar tissueForm the blood-brain barrier

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NEUROGLIAL CELLSOligodendrocytesinterfascicularProduce myelin sheath (electrical insulation) in CNSA single cell wrap several axons (40 to 50)Form nodes of Ranviersatellite

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NEUROGLIAL CELLSSchwann cellsAnalogue to OligodendrocyteProduce myelin sheath in the PNS

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NEUROGLIAL CELLSMicrogliaScattered throughout the CNSClearing debrisAct as APCProtect the CNS from viruses and microorganism

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NEUROGLIAL CELLSEpendymal CellsLow columnar ciliated epithelial cells line the ventricles of the brain & central canal spinal cordFormation of choroid flexus produce CSFFacilitates the movement of CSF

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THE CNSConsist of :CerebrumCerebellumSpinal cordNo connective tissue soft, gel likeWhen sectioned :White matterGray matterCovered by meninges**

CEREBRUMGRAY MATTERContains neuronal cell bodies, dendrites and glial cellsSix layers composed of neuronNeuron (pyramidal):Afferent (sensory)Efferent (motor)WHITE MATTERContains myelinated axons and myelin-producing oligodendrocytes **

CEREBELLUMGRAY MATTERThree layers :Outer molecular layerCentral layer of large Purkinje cellsInner granule layerWHITE MATTERThe same as cerebrum

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SPINAL CORDGRAY MATTER (CENTRAL)SHAPE OF HCentral canal lined by Ependymal cellsLegs of the H form :Anterior hornsPosterior hornsNeurons : large and multipolarWHITE MATTER (PERIPHERAL)

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PNSBundles of nerve fibers (axons) outside the CNS & surrounded by connective tissue

Main component :Peripheral nervesGangliaNerve endings

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NERVE FIBERSConsist of axons enveloped by a special sheathGroup of fibers constitute the peripheral nerveTwo types :Myelinated fiberUnmyelinated fiber

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NERVE FIBERSMyelinated fibersA single Schwann cell wraps around single axon form myelin sheath nodes of RanvierUnmyelinated fibersA single Schwann cell envelopes several axonFibers enveloped within simple clefts of Schwann cells

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CONNECTIVE TISSUE INVESTMENTSEpineureum Dense collagenous Con. Tissue with thick elastic fiberPrevent damage by overstrechingPerineureum Dense con. TissueLayers of epithelioidsIsolates neural environment (blood-nerve barrier)Endoneureum Loose con. TissueRegulation of microenvironment of nerve fiber

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GANGLIAOvoid structure containing neuronal cell bodies, glial cells supported by connective tissueFunction : Relay stations to transmit impulsesTypes :Sensory gangliaAutonomic ganglia **

DORSAL ROOT GANGLIA

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GANGLIASensory Ganglia (cell bodies of sensory neuron)Unipolar cell bodies enveloped by cuboidal capsule cellsCranial ganglia : Associated with the cranial nerveSpinal ganglia : Associated with the spinal nerve

Autonomic Ganglia (cell bodies of postganglionic autonomic nerves)Multipolar neuron enveloped by satellite cellsSome are located within certain organ (intramural) **

FUNCTIONAL CLASSIFICATION OF NERVESSensory nerve fibersCarry sensory input from the cutaneus/ viscera area to CNSMotor nerve fibersOriginate in the CNS carry motor impulses to the effector organs

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MENINGESThe dura mater dense, collagenous connective tissueThe arachnoid layer:fibroblasts, collagen & elastic fibersLayer in contact with dura mater & a system of trabeculaeForm arachnoid villiThe pia materLoose con. Tissue with blood vessel **

BLOOB-BRAIN BARRIEREndothelial of capillaryOccluding junctionNo fenestrationExpansions of Astrocytes cell processes that envelope the capillary

permeability**Prevents the passage of substances (bacterial, toxic, Chemical) from blood to nerve tissue

CHOROID FLEXUS Choroid flexus consist of loose conn. tissue of the pia matter, covered by a low columnar epith. ion transporting cellsElaborate CSF fill the ventricles subarachnoid space (arachnoid villi)venousCSF metabolism and protective of CNS**

CEREBROSPINAL FLUID Composition clear, low density & protein contentHigh Na, K, ClFunctionMetabolicLiquid cushionBlood-CSF barrierZonulae occludents

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REFFERENCESColor Textbook Histology, third edition, leslie P. GartnerBasic Histology, tenth edition, L. Carlos Junqueira,2003Histology and Cell Biology, second edition,2007Elseviers Integrated Histology,2007**

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