Presentation on theme: "11 Fundamentals of the Nervous System and Nervous Tissue: Revised by Dr. Par Mohammadian."— Presentation transcript:
1 11Fundamentals of the Nervous System and Nervous Tissue: Revised by Dr. Par Mohammadian
2 Master controlling and communicating system of body The Nervous SystemMaster controlling and communicating system of bodyCells communicate via electrical and chemical signalsRapid and specific
3 Functions of the Nervous System Sensory inputInformation gathered by sensory receptors about internal and external changesIntegrationProcessing and interpretation of sensory inputMotor outputActivation of effector organs (muscles and glands) produces a response
5 Divisions of the Nervous System Central nervous system (CNS)Brain and spinal cord of dorsal body cavityIntegration and control centerInterprets sensory input and dictates motor outputPeripheral nervous system (PNS)The portion of the nervous system outside CNSConsists mainly of nerves that extend from brain and spinal cordSpinal nerves to and from spinal cordCranial nerves to and from brain
6 Peripheral Nervous System (PNS) Two functional divisionsSensory (afferent) divisionSomatic sensory fibers—convey impulses from skin, skeletal muscles, and joints to CNSVisceral sensory fibers—convey impulses from visceral organs to CNSMotor (efferent) divisionTransmits impulses from CNS to effector organsMuscles and glandsTwo divisionsSomatic nervous systemAutonomic nervous system
7 Motor Division of PNS: Somatic Nervous System Conscious control of skeletal musclesAutonomic Nervous SystemRegulates smooth muscle, cardiac muscle, and glandsTwo functional subdivisionsSympatheticParasympathetic
8 Somatic nervous system Central nervous system (CNS)Peripheral nervous system (PNS)Brain and spinal cordCranial nerves and spinal nervesIntegrative and control centersCommunication lines between the CNSand the rest of the bodySensory (afferent) divisionMotor (efferent) divisionSomatic and visceral sensorynerve fibersMotor nerve fibersConducts impulses from the CNSto effectors (muscles and glands)Conducts impulses fromreceptors to the CNSSomatic nervoussystemAutonomic nervoussystem (ANS)Somatic sensory fiberSkinSomatic motor(voluntary)Visceral motor(involuntary)Conducts impulsesfrom the CNS toskeletal musclesConducts impulsesfrom the CNS tocardiac muscles,smooth muscles,and glandsVisceral sensory fiberStomachSkeletalmuscleMotor fiber of somatic nervous systemSympathetic divisionParasympatheticdivisionMobilizes body systemsduring activityConserves energyPromotes house-keeping functionsduring restSympathetic motor fiber of ANSHeartStructureFunctionSensory (afferent)division of PNSParasympathetic motor fiber of ANSBladderMotor (efferent)division of PNS
9 Histology of Nervous Tissue Highly cellular; little extracellular spaceTightly packedTwo principal cell typesNeuroglia – small cells that surround and wrap delicate neuronsNeurons (nerve cells)—excitable cells that transmit electrical signals
11 Astrocytes Most abundant and highly branched glial cells Cling to neurons, synaptic endings, and capillariesFunctions includeSupport neuronsPlay role in exchanges between capillaries and neuronsControl chemical environment around neuronsRespond to nerve impulses and neurotransmitters
12 Capillary Neuron Astrocyte Astrocytes are the most abundant CNS neuroglia.
13 Microglial Cells Neuron Microglial cell Can transform to phagocytizeSmall, ovoid cells with thorny processesNeuronMicroglialcellMicroglial cells are defensive cells in the CNS.
14 Ependymal Cells Fluid-filled cavity Range in shape from squamous to columnarMay be ciliatedCilia beat to circulate cerebrospinal fluid (CSF)Line the central cavities of the brain and spinal columnForm permeable barrier between CSF in cavities and tissue fluid bathing CNS cellsFluid-filled cavityCiliaEpendymalcellsBrain orspinal cordtissueEpendymal cells line cerebrospinal fluid–filled cavities.
15 Oligodendrocytes Myelin sheath Process of oligodendrocyte Nerve fibers Branched cellsProcesses wrap CNS nerve fibers, forming insulating myelin sheaths thicker nerve fibersMyelin sheathProcess ofoligodendrocyteNervefibersOligodendrocytes have processes that form myelinsheaths around CNS nerve fibers.
16 Satellite Cells and Schwann Cells (PNS) Surround neuron cell bodies in PNSFunction similar to astrocytes of CNSSchwann cells (neurolemmocytes)Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibersSimilar function as oligodendrocytesVital to regeneration of damaged peripheral nerve fibers
17 SatellitecellsCell body of neuronSchwann cells(forming myelin sheath)Nerve fiberSatellite cells and Schwann cells (which form myelin)surround neurons in the PNS.
18 NeuronsStructural units of nervous systemLarge, highly specialized cells that conduct impulsesHigh metabolic rate—requires continuous supply of O2 and glucose – cannot survive for more than a few minutes without O2!All have cell body (soma) and one or more processes
19 Processes Armlike extensions from the soma Dendrites(receptiveregions)Cell body(biosynthetic center& receptive region)Armlike extensions from the somaCalled tracts in the CNS and nerves in the PNSThere are two types: axons and dendritesNucleusAxon(impulse-generatingand -conductingregion)Myelin sheath gap(node of Ranvier)NucleolusImpulsedirectionChromatophilicsubstance (roughendoplasmicreticulum)Axonterminals(secretoryregion)Schwann cellAxon hillockTerminal branches
20 Nerve Cell Body (Perikaryon or Soma) Contains the nucleus and a nucleolusIs the major biosynthetic centerIs the focal point for the outgrowth of neuronal processesHas well-developed Nissl bodies (rough ER)Contains an axon hillock – cone-shaped area from which axons arise
21 Nuclei & GangliaMost neuron cell bodies located in the CNS – protected by the bones, skull, and vertebral column: NucleiCell bodies located in the PNS: ganglia
22 Dendrites In motor neurons Receptive (input) region of neuron 100s of short, tapering, diffusely branched processesReceptive (input) region of neuronNeuron cell bodyDendriticspine
23 The Axon: Structure One axon per cell arising from axon hillock Long axons called nerve fibersOccasional branches (axon collaterals)Branches profusely at end (terminus)Distal endings called axon terminals or terminal boutonsFunction:Generates nerve impulsesTransmits them along axolemma (neuron cell membrane) to axon terminalSecrete neurotransmitters from the axonal terminals
24 Myelin SheathWhitish, fatty (protein-lipoid), segmented sheath around most long axonsIt functions to:Protect the axonElectrically insulate fibers from one anotherIncrease the speed of nerve impulse transmission
25 Myelin Sheath and Neurilemma: Formation Formed by Schwann cells in the PNS and Oligodendrocytes in the CNSA Schwann cell:Envelopes an axon in a troughEncloses the axon with its plasma membraneHas concentric layers of membrane that make up the myelin sheathNeurilemma – remaining nucleus and cytoplasm of a Schwann cellNodes of Ranvier: Gaps in the myelin sheath between adjacent Schwann cells
26 Schwanncell plasmamembraneA Schwann cell envelops an axon.1Schwann cellcytoplasmAxonSchwann cellnucleusThe Schwann cell then rotatesaround the axon, wrapping itsplasma membrane loosely aroundit in successive layers.2The Schwann cell cytoplasm isforced from between the membranes.The tight membrane wrappingssurrounding the axon form the myelinsheath.3MyelinsheathSchwann cell cytoplasmMyelination of a nerve fiber (axon)
27 Myelin Sheaths in the CNS White matterdense collections of myelinated fibersGray matterMostly neuron cell bodies and nonmyelinated fibers
28 Structural Classification of Neurons Multipolar – 3 or more processes1 axon, others dendritesMost common; major neuron in CNSBipolar – 2 processes1 axon and 1 dendriteRare, e.g., Retina and olfactory mucosaUnipolar – 1 short processDivides T-like – both branches now considered axonsDistal (peripheral) process – associated with sensory receptorProximal (central) process – enters CNS
31 Table 11.1 Comparison of Structural Classes of Neurons (3 of 3)
32 Functional Classification of Neurons SensoryTransmit impulses from sensory receptors toward CNSMotorCarry impulses from CNS to effectorsInterneurons (association neurons)Shuttle signals through CNS pathways; most are entirely within CNS99% of body's neuronsMost confined in CNS