Chapter 7: The Nervous System

Chapter 7: The Nervous SystemAnatomy & Physiology

Functions of the Nervous SystemNervous System manages body via electrical impulsesSensory inputgathering informationMonitor changes occurring inside and outside the bodyChanges = stimuli Internal vs externalIntegrationProcesses and interprets sensory input Decide if/what action is neededMotor outputA response to integrated stimuliBy activating muscles or glands

Functions of the Nervous System

Structural Classification of the Nervous SystemCentral nervous system (CNS)BrainSpinal cordPeripheral nervous system (PNS)Nerves outside the brain and spinal cordSpinal nervesCranial nerves

Classification of the Peripheral Nervous SystemSensory (afferent) divisionNerve fibers that carry information to the central nervous systemVia sensory fibers found in:SkinSkeletal musclesJoints

Motor (efferent) divisionNerve fibers that carry impulses away from the central nervous system

Motor (Efferent) DivisionSomatic nervous system = voluntarySystem that we consciously controlI.E. contracting muscles on demandAutonomic nervous system = involuntarySystem that is activated subconsciouslyI.E. cardiac muscles, glands, respiratory rate

Organization of the Nervous System

Nervous Tissue: Support CellsAstrocytesAbundant, star-shaped cellsBrace neuronsForm barrier between capillaries and neuronsControl the chemical environment of the brain

Nervous Tissue: Support CellsMicrogliaSpiderlike phagocytesDispose of debrisi.e. dead brain cellsbacteria

Nervous Tissue: Support CellsEpendymal cellsLine cavities of the brain and spinal cordCirculate cerebrospinal fluid w/ cilia

Nervous Tissue: Support CellsOligodendrocytesWrap around nerve fibers in the central nervous system to form myelin sheathsSchwann cellsForm myelin sheath in the peripheral nervous systemInclude neurilemma.Satellite cellsProtect neuron cell bodies

Nervous Tissue: NeuronsNeurons = nerve cellstransmit messagesMajor regions of neuronsCell bodynucleus and metabolic center of the cellProcessesfibers that extend from the cell body Cell bodyNissl substanceSpecialized rough endoplasmic reticulumNeurofibrils Intermediate cytoskeleton Maintains cell shape

Nervous Tissue: NeuronsCell bodyNucleusLarge nucleolusProjections outside the cell bodyDendritesconduct impulses toward the cell bodyAxonsconduct impulses away from the cell body

Nervous Tissue: NeuronsAxons end in axonal terminalscontain vesicles with neurotransmittersNeurons dont touch each other rather are separated by a gapSynaptic cleftgap between adjacent neuronsSynapsejunction between nerves

Nervous Tissue: NeuronsMyelin sheathwhitish, fatty material covering axons increases speed of nerve impulsesSchwann cellsproduce myelin sheaths in jelly rolllike fashionNodes of Ranviergaps in myelin sheath along the axon

Neuron Cell Body LocationMost neuron cell bodies are found in the central nervous systemGray mattercell bodies and unmyelinated fibersGangliacollections of cell bodies outside the central nervous systemTracts are nerve fibers traveling through the CNSNerves nerve fibers traveling through PNSFunctional Classification of NeuronsSensory (afferent) neuronsCarry impulses from the sensory receptors to the CNSReceptorsCutaneous sense organs Proprioceptorsdetect stretch or tension in muscles, tendons, jointsBrain makes adjustments for posture and balanceMotor (efferent) neuronsCarry impulses from the central nervous system to viscera, muscles, or glands to illicit reactionInterneurons (association neurons)Found in neural pathways in the CNSConnect sensory and motor neurons

Structural Classification of NeuronsMultipolar neurons many extensions (processes) from the cell bodyCommon Location: Motor neurons

21Structural Classification of NeuronsBipolar neurons one axon and one dendriteRareCommon locations: Special sense organs (i.e. ears, nose, eyes)

Structural Classification of NeuronsUnipolar neurons have a short single process leaving the cell body1 process onlyAxon: Includes CNS and PNS extensionCommon Location: Sensory Neurons in PNS

Physiology of Nerve ImpulsesNeurons function in 2 ways:Irritability: Respond to stimulus and translate it into a nerve impulseConductivity: Transport impulse to necessary location (i.e. other neurons, muscles, glands, organs)

Physiology of Nerve ImpulsesMembrane of NeuronAt rest: Membrane is impermeable to sodium ions1)When activated: sodium ions rush into the neuron cell body. How are they activitaed?By external stimulus (i.e. light-eye, smell-nose, sound-ear)Most commonly by neurotransmitters 2)Depolarization occurs (sodium-potassium pump: more sodium in than out) and results in a graded potential3) If graded potential is strong enough it leads to.Action potential/nerve impulsePhysiology of Nerve Impulses4) Repolarization:Membrane becomes impermeable againSodium goes outside cell body, potassium goes insideRestores natural stateAnother impulse cannot be initiated until repolarization occursUses what energy?Myelin sheaths role:Causes impulse to travel faster byNerve impulse leaps OVER sheaths because it cant travel through fatPhysiology of Nerve ImpulsesHow does nerve impulse travel throughout neurons?Electrical chemical event:Impulse cannot go past axon terminalsVesicles release neurotransmittersThey travel across synaptic cleftBind to receptors on the dendrites of the next neuronInitiate process of nerve impulse all over again

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AxonterminalVesiclesSynapticcleftActionpotentialarrivesSynapseAxon oftransmittingneuronReceivingneuronThe Reflex ArcReflex: A programmed, rapid, involuntary response to stimuliReflex arcs: Neural pathways that reflexes travel

2 types of Reflexes:Somatic: Reflexes involving skeletal musclei.e. removing hand from hot ironAutonomic: Regulate smooth muscles organs, breathing rate, BPThe Reflex ArcReflex arcs made up of a minimum of 5 stepsSensory ReceptorSensory NeuronIntegration CenterMotor NeuronEffector

Stimulus at distalend of neuronSkinSpinal cord(in cross section) InterneuronReceptorEffectorSensory neuronMotor neuronIntegrationcenter(a)Regions of the Brain

Cerebrum (Cerebral Hemispheres)DiencephalonBrain StemCerebellumRegions of the BrainCerebrum (Cerebral Hemispheres)

Paired (left & right) superior parts of the brainIncludes more than half of the brain massThe surface is made of ridges (gyri) and grooves (sulci)

Regions of the Brain-CEREBRUMLobes of the cerebrumFissures (deep grooves) divide the cerebrum into lobesSurface lobes of the cerebrumFrontal lobeParietal lobeOccipital lobeTemporal lobe

Specialized areas of the cerebrumPrimary somatic sensory areaReceives impulses from the bodys sensory receptors(i.e. cold, pain, touch)Located in parietal lobePrimary motor areaSends impulses to skeletal musclesLocated in frontal lobeBrocas AreaInvolved in our area to speakRegions of the Brain-CEREBRUM

erebral areas involved in special sensesGustatory area (taste)Location: Parietal lobeHelps detect different tastes in foodsVisual areaLocation: Occipital lobeRecognition based on past experiencesAuditory areaLocation: Temporal LobeRecognition/perception of soundsOlfactory areaLocation: Medial Temporal LobeConscious awareness of scentsRegions of the Brain-CEREBRUM

Interpretation areas of the cerebrumLocated across both hemispheres (temporal, occipital, parietal lobes)Speech/language regionHelps with understanding written/spoken languageLanguage comprehension regionLanguage/Reading comprehensionGeneral interpretation areaStores complex memoriesRecognizes different senses/signals and puts them into a cognitive thoughtRegions of the Brain-CEREBRUM

Regions of the Brain-CEREBRUMLayers of the cerebrumGray matterouter layer in the cerebral cortex composed mostly of neuron cell bodiesWhite matterfiber tracts deep to the gray matterCorpus callosum connects hemispheresAllows communication between themBasal nucleisections of gray matter buried within the white matterAdapts voluntary motor movements to changes

Regions of the Brain: DiencephalonSits on top of the brain stemEnclosed by the cerebral hemispheresMade of three partsThalamusHypothalamusEpithalamus

DiencephalonTHALAMUSHYPOTHALAMUSFUNCTIONS:Transports all sensory signals/impulses to the cerebral cortex (cerebrum)Deals with sensations such as pain and temperatureFUNCTIONS:Transports and receives signals/impulses from the cerebrum and thalamusWorks closely with the pituitary glandHelps produce hormones to regulate activity of organsHungerMetabolismBody TemperatureSleepEmotions

DiencephalonEPITHALAMUSHouses the pineal body (an endocrine gland)Includes the choroid plexusforms cerebrospinal fluid

Regions of the Brain: Brain StemAttaches to the spinal cordParts of the brain stemMidbrainPonsMedulla oblongata

Regions of the Brain: Brain StemMIDBRAINPONSLocation:Between pons and diencephalonNerve fibers join brain stem and spinal cord to cerebrumFunctions: Controls vision and hearingRounded bulge on brain stemBetween midbrain and medulla oblongataFunctions:Control swallowing CN: VHelps in facial movementCN VIIMEDULLA OBLONGATALOCATION:Between pons and spinal cordFunctions:Receives and interprets signals from spinal cordControls vital signs Respiration (breathing rate)CirculationBlood pressureCoughingHeart beat (Beats per minute)

Regions of the Brain: Brain StemRegions of the Brain: Brain StemReticular Formation Diffuse mass of gray matter along the brain stemPlays a role in awake/sleep cycles and consciousness

Regions of the Brain: CEREBELUMCerebellum a.k.a. little brainLocation: Attaches to brainstem and behind ponsFunctions:Center for balanceMotor controlActivates receptors in muscles, tendons, and joints

Protection of the Central Nervous SystemStructures that offer protection:Scalp and skinSkull and vertebral columnMeningesCerebrospinal fluid (CSF)Blood-brain barrier

Protection of the Central Nervous SystemMENINGES: cover and protect CNSMade of 3 layersDura materArachnoid materPia mater

Protection of the Central Nervous SystemDURA MATERARACHNOID MATEROutermost layerAttaches superiorly to skullMade of thick, fibrous tissueContains blood vessels and nerves

Middle layerThin, cobweb like structureBlood vesselsReabsorbs CSFPIA MATERInner most layerClings to brain and spinal cordContains several blood vesselsCerebrospinal Fluid (CSF)Clear, grayish fluid that lubricates Brain and Spinal CordSuspends brain within skullFormed from blood and choroid plexusesOffers nutrients that CNS nerves requireCan be tested in a Spinal TapCan detect MS, tumors, or meningitis

HydrocephalusCSF accumulates and exerts pressure on the brain if not allowed to drainCerebrospinal Fluid (CSF)

Blood-Brain BarrierIncludes the least permeable capillaries of the bodyExcludes many potentially harmful substancesAllows entry to:Water-soluble elementsGlucoseEssential amino acidsCant protect itself from these substances:Fats and fat soluble moleculesRespiratory gasesAlcoholNicotineAnesthesia

Traumatic Brain InjuriesConcussionSlight brain injuryNo permanent brain damageContusionNervous tissue destruction occursNervous tissue does not regenerateCerebral edemaSwelling from the inflammatory responseMay compress and kill brain tissue

Cerebrovascular Accident (CVA)Commonly called a strokeThe result of a ruptured blood vessel supplying a region of the brainBrain tissue supplied with oxygen from that blood source diesLoss of some functions or death may resultParalysis on one side of the bodyAphasiaAlzheimers DiseaseProgressive degenerative brain diseaseMostly seen in the elderly, but may begin in middle ageCauses:Excessive protein depositsDecreased levels of AchResults in brain atrophyGeneticsNeuron fibers become twistedVictims experience memory loss, irritability, confusion, and ultimately, hallucinations and death