Chapter 12 – Introduction to the Nervous System

  • View

  • Download

Embed Size (px)


Chapter 12 Introduction to the Nervous System. Organization Cell Types. Review. What 3 parts make up the nervous system? Brain Spinal cord Nerves. Functions of the Nervous System. - PowerPoint PPT Presentation


  • Chapter 12 Introduction to the Nervous System Organization Cell Types

  • ReviewWhat 3 parts make up the nervous system?

    Brain Spinal cordNerves


  • Functions of the Nervous SystemDetect changes (stimuli) in the internal or external environmentEvaluate the informationInitiate a change in muscles or glands

    Goal maintain homeostasis

    What does this remind you of??

  • Organization of the Nervous SystemCentral nervous system (CNS)Brain and spinal cordPeripheral nervous system (PNS)Nervous tissue in the outer regions of the nervous systemCranial nerves: originates in the brainSpinal nerves : originates from the spinal cordCentral fibers: extend from cell body towards the CNSPeripheral fibers: extend from cell body away from CNS


  • Afferent vs EfferentNervous pathways are organized into division based on the direction they carry informationAfferent division: incoming information (sensory)Efferent division: outgoing information (motor)(Efferent = Exit)

  • Somatic & Autonomic Nervous SystemsNervous pathways are also organized according to the type of effectors (organs) they regulateSomatic nervous system (SNS)Somatic sensory division (afferent)Somatic motor division (efferent)

  • Somatic & Autonomic Nervous Systems contAutonomic nervous system (ANS): Carry information to the autonomic or visceral effectors (smooth & cardiac muscles and glands)Visceral sensory division (afferent)Efferent pathwaysSympathetic division fight or flightParasympathic division rest and repair

  • Figure 12-2


  • ReviewWhat are the two main cell types in the nervous system?(Hint: we talked about this when we covered tissue types)

    Answer: neurons and glia

  • Cells of the Nervous SystemNeurons: excitable cells that conduct information

    Glia (also neuroglia or glial cells): support cells, do not conduct informationMost numerousGlia = glue

  • Types of GliaFive major types:AstrocytesMicrogliaEpendymal cellsOligodendrocytesSchwann cells

  • Astrocytes (12-3A)Star-shaped, largest, most numerousCell extension connect neurons and capillariesTransfer nutrients from blood to neuronHelp form blood-brain barrier (BBB)

  • Blood-Brain BarrierHelps maintain stable environment for normal brain functionfeet of astrocytes wrap around capillaries in brainRegulates passage of ionsWater, oxygen, CO2, glucose and alcohol pass freelyImportant for drug researchParkinsons Disease

  • Microglia (12-3B)Engulf and destroy cellular debris (phagocytosis)Enlarge during times of inflammation and degeneration

  • Ependymal cells (12-3C)Similar to epithelial cells Forms thin sheets that line the fluid-filled cavities of the brain and spinal cord Some cells help produce the fluid that fills these cavities (cerebral spinal fluid - CSF)Cilia may be present to help circulate fluid

  • Oligodendrocytes (12-3D)Hold nerve fibers togetherProduce myelin sheaths in CNS

  • Multiple Sclerosis (MS)Most common myelin disorderCharacterized by:myelin loss and destruction injury and death plaque like lesionsImpaired nerve conduction weakness, loss of coordination, vision and speech problemsRemissions & relapses Autoimmune or viral infectionWomen 20-40 yrsNo known cure

  • Multiple Sclerosis (MS)

  • Schwann cells (12-3E)Only in PNSSupport nerve fibers & form myelin sheathsSatellite cells (12-3G)Types of schwann cell that covers a neurons cell body


  • NeuronsAll neurons have 3 parts:Cell body (soma)AxonOne or more dendrites

  • Neuron AnatomySoma resembles other cellsNissl bodies part of rough ER; contain proteins necessary for nerve signal transmission & nerve regenerationDendrites branch out from soma; receptors; conduct impulse towards somaAxon process that extends from the soma at a tapered portion called the axon hillockAxon collaterals: side branchesTelodendria: distal branches of axonSynaptic knob: ends of telodendria


  • Neuron AnatomyMyelin sheaths: areas of insulation produced by Schwann cells; increases speed of nerve impulseMyelinated = white matterUnmyelinated = gray matterNodes of Ranvier: breaks in myelin sheath btwn Schwann cellsSynapse: junction btwn two neurons or btwn a neuron and an effector


  • Structural Classification of NeuronsMultipolarOne axon, several dendritesMost numerousBipolarOne axon, one dendriteLeast numerousRetina, inner ear, olfactory pathwayUnipolarAxon is a single process that branches into a central process (towards CNS) and a peripheral process (towards PNS)Dendrites at distal end of peripheral processAlways sensory neurons


  • Functional Classification of NeuronsAfferentSensoryTowards CNSEfferent MotorTowards muscles & glandsInterneuronsConnect afferent & efferent neuronsLie within CNS

  • Reflex Arc

  • Examples of Reflex ArcsIpsilateralContralateralintersegmental

  • Nerves vs TractsNerves bundles of parallel neurons held together by fibrous CT in the PNSTracts bundles of parallel neurons in the CNS

  • Nerve FibersRemember the difference between nerves and tracts?Endoneurium: surrounds each nerve fiberPerineurium: surrounds fascicles (bundles of nerve fibersEpineurium: surrounds a complete nerve (PNS) or tract (CNS)

  • Review: Gray vs White MatterWhite matter myelinated nerve fibersMyelin sheaths help increase the speed of an action potentialGray matter unmyelinated nerve fibers & cell bodiesGanglia: regions of gray matter in PNS

  • Nerve Fiber RepairNervous tissue has a limited repair capacity b/c mature neurons are incapable of cell divisionRepair can take place if soma and neurilemma remain intact

  • Steps of Nerve Fiber RepairInjuryDistal axon and myelin sheaths degeneratesRemaining neurilemma & endoneurium forms a tunnel from the injury to the effectorProteins produced in the nissl bodies help extend a new axon down the tunnel to the effector

  • Nerve ImpulsesNeurons are specialized to initiate and conduct signals nerve impulsesExhibit excitability & conductivityNerve impulse wave of electrical fluctuation that travels along the plasma membrane

  • Membrane PotentialsDifference in charges across the plasma membraneInside slightly negative Outside slightly positiveResult in a difference in electrical charges membrane potential Stored potential energyAnalogy = water behind a dam

  • Membrane PotentialsMembrane potential creates a polarized membraneMembrane has pole & + polePotential difference of a polarized membrane is measured in millivolts (mV)The sign indicates the charge of the inside of a polarized membrane

  • Resting Membrane Potential (RMP)When not conducting electrical signals, a membrane is resting-70mVRMP maintained by ionic imbalance across membraneSodium-Potassium PumpPumps 3 Na+ out for every 2 K+ pumps inCreates an electrical gradient (more positive on outside)

  • Resting Membrane Potential (RMP)

  • Local PotentialLocal potential - The slight shift away from the RMPIsolated to a particular region of the plasma membraneStimulus-gated Na+ channels open Na+ enters membrane potential to moves closer to zero (depolarization)Stimulus-gated K+ channels open K+ exits membrane potential away from zero (hyperpolarization)**Local potentials do not spread to the end of the axon**

  • Local Potentials

  • Action Potentials Definitions:Membrane potential of an active neuron (one that is conducting an impulseAction potential = nerve impulseAn electrical fluctuation that travels along the plasma membrane

  • Steps of Producing an Action Potential (table 12-1)A stimulus triggers stimulus-gated Na+ channels to open Na+ diffuses inside the cell depolarizationThreshold potential is reached (-59mV) voltage-gated Na+ channels open depolarization continuesAction potential peaks at +30mV, voltage-gated Na+ channels closeVoltage-gated K+ channels open K+ diffuses outward repolarizationBrief period of hyperpolarization (below -70mV) RMP is restored by Na+/K+ pump

  • Refractory Period

  • Refractory PeriodPeriod of time where the neuron resists restimulation (AP cannot fire)Absolute refractory period: half a millisecond after membrane reaches threshold potential Will not respond to ANY stimulusRelative refractory period: few milliseconds after absolute refractory period (during repolarization)Only respond to VERY strong stimulus

  • Refractory Period What does this