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Introduction and Basic Structural Organization of the Nervous System

Introduction and Basic Structural Organization of the Nervous System. Lecture Objectives. Describe the organization of the NS. Overview of the main parts of the CNS. Identify the main parts of the brain in CT scan and MRI. Describe the surface anatomy of the brain.

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Introduction and Basic Structural Organization of the Nervous System

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  1. Introduction and Basic Structural Organization ofthe NervousSystem

  2. LectureObjectives • DescribetheorganizationoftheNS. • OverviewofthemainpartsoftheCNS. • IdentifythemainpartsofthebraininCTscanandMRI. • Describethesurfaceanatomyofthebrain. • Briefly describe thebrain ventricles and meninges. • Explain theconcept of nuclei, fasciculi, lemnisci, tracts, laminae, whiteandgraymatterinputs(afferent)andoutputs(efferent).

  3. INTRODUCTION • The nervoussystem,along with the endocrinesystem,helpstokeepcontrolled conditions within limits that maintain healthandhelpstomaintainhomeostasis. • The nervous system is responsible for all ourbehaviors,memories,andmovements. • The branch of medical science that deals withthenormalfunctioninganddisorders ofthenervoussystemiscalledneuoogy.lr

  4. Major Structures of the NervousSystem • CNS • Brain and SpinalCord • PNS • cranialnerves,spinalnerves,ganglia,entericplexusesandsensoryreceptors

  5. Nervous SystemDivisions • Central nervous system(CNS) • consistsofthebrainandspinalcord • Peripheral nervous system(PNS) • consistsofcranialandspinalnervesthatcontainbothsensory and motorfibers • connects CNS to muscles, glands & all sensoryreceptors

  6. Functions of the NervousSystems • The sensory functionofthe nervous system is to sense changes in the internalandexternalenvironmentthroughsensoryreceptors. • Sensory(afferent)neuronsservethisfunction. • The integrative functionisto analyze the sensory information, store someaspects,andmakedecisionsregardingappropriatebehaviors. • Associationorinterneuronsserve thisfunction. • Themotorfunctionistorespondtostimulibyinitiatingaction. • Motor(efferent)neuronsservethisfunction.

  7. Subdivisions of thePNS • Somatic (voluntary) nervous system(SNS) • neuronsfromcutaneousandspecialsensoryreceptorstothe CNS • motorneuronstoskeletalmuscletissue • Autonomic (involuntary) nervoussystems • sensoryneuronsfromvisceralorganstoCNS • motorneuronstosmooth&cardiacmuscleandglands • sympatheticdivision(speedsupheartrate) • parasympathetic division (slow down heartrate)

  8. Gray and WhiteMatter • White matter= myelinated processes (white in color) • Gray matter = nerve cell bodies, dendrites,axon terminals, bundlesofunmyelinatedaxonsandneuroglia(graycolor) • Inthespinalcord=graymatterformsanH-shapedinnercore surrounded by whitematter • Inthebrain=athinoutershellofgraymattercoversthesurface & is found in clusters called nuclei inside theCNS

  9. The Spinal Cord & SpinalNerves • Together with brain forms theCNS • Functions • spinal cordreflexes • integration (summation ofinhibitory and excitatory) nerveimpulses • highway for upward anddownward travel of sensory and motor information

  10. Spinal CordProtection By thevertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

  11. Structures Covering the SpinalCord • Bones(Vertebrae) • Epidural space filled withfat • Meninges • Duramater • dense irregular CTtube • Subdural space filledwith interstitialfluid • Arachnoid = spider webof collagenfibers • Subarachnoid space =CSF • Piamater • thin layer coversBV • denticulate ligs hold inplace

  12. Gray Matter of the SpinalCord • GraymatterisshapedliketheletterHorabutterfly • contains neuroncell bodies, unmyelinated axons & dendrites • paired dorsal andventral gray horns • lateralhornsonlypresentinthoracicspinalcord • gray commissure crosses themidline • Centralcanalcontinuouswith4thventricleofbrain

  13. White Matter of theSpinal Cord • White matter covers graymatter • AnteriormedianfissuredeeperthanPosteriormediansulcus • Anterior, Lateral and Posterior White Columns contain axonsthat form ascending & descendingtracts

  14. SpinalNerves • 31 Pairs of spinalnerves • Named & numbered bythe cord level of theirorigin • 8 pairs of cervicalnerves • 12 pairs of thoracicnerves • 5 pairs of lumbarnerves • 5 pairs of sacralnerves • 1 pair of coccygealnerves • Mixed sensory & motornerves

  15. The Brain and CranialNerves

  16. Principal Parts of theBrain • Cerebrum • Cerebralhemispheres • Corpuscallosum • Diencephalon • thalamus, hypothalamus,& epithalamus • Cerebellum • Brainstem • medulla, pons &midbrain

  17. Principal Parts of theBrain

  18. Brain CTscan

  19. BrainMRI

  20. Prote ctive Coverings of theBrain • Bone, meninges &fluid • Meninges same as aroundthe spinalcord • duramater • arachnoidmater • piamater • Dura materextensions • falxcerebri • tentoriumcerebelli • falxcerebelli

  21. Ventricles • 2lateralventricles,onewithineachcerebralhemisphere • 3rdventricle • fourthventricle

  22. Ventricles • Choroid plexus = capillaries covered by ependymalcells • ProductionCSF

  23. CranialNerves • Thecranialnervesarepartoftheperipheralnervous system • There are 12 pairs ofCranial nerves • All cranial nerves travel through foramina of theskull • 10pairsoriginatefromthebrainstem(III-XII) • The cranial nerves are designatedby: • Romannumeralswhichindicatetheorderinwhichthenerves arisefromthebrainfromanteriortoposterior • Nameswhichindicatethedistributionorfunction

  24. CranialNerves • Twocranialnerves(IandII)containonlysensoryfibersandare therefore called sensorynerves • Theothercranialnervescontainbothsensoryandmotorfibers andarethereforecalledmixednerves • Someofthemixednervesareprimarilymotorinfunction(butcontain proprioceptivefibers). • Thecellbodiesofsensoryfibersarelocatedingangliaoutside thebrain. • Thecellbodiesofmotorfibersarelocatedinnucleiwithinthe brain • Somecranialnervesincludebothsomaticmotorandparasympathetic fibersoftheautonomicnervoussystem.

  25. Cranial Nerves: Types ofFibers

  26. CranialNerves

  27. Ganglia Vs.Nuclei • Both are clusters of neuronsto form functionalunit • Nuclei inCNS • Ganglia inPNS • Sensory ganglia(DRG) • Autonomicganglia

  28. Fasciculi, Lemnisci, & Tracts • All are bundles of nerve fibersin theCNS • Lemniscus is a bundle ofnerve fibers of second order sensory neurons • Medial & laterallemnisci • Tracts orfasciculi • Gracile & cuneatefasciculi • Ascending and descendingtracts

  29. Afferent Vs.Efferent • PNS • Afferent – Sensoryfibers • Efferent – Motorfibers • SC • Afferent – Ascendingtracts • Efferent – Descendingtracts • Brainparts • Afferent –Inputs • Efferent –Outputs

  30. Laminae • Thin plates or layers of thegray matter ofCNS • Laminae of cerebralcortex • Rexed laminae of spinalcord

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