Y khoa, y dược - The central nervous system: Part A

12The Central Nervous System: Part ACentral Nervous System (CNS)CNS consists of the brain and spinal cordCephalizationEvolutionary development of the rostral (anterior) portion of the CNSIncreased number of neurons in the headHighest level is reached in the human brainEmbryonic DevelopmentNeural plate forms from ectoderm Neural plate invaginates to form a neural groove and neural foldsFigure 12.1, step 1The neural plate forms from surface ectoderm.1HeadTailSurfaceectodermNeuralplateFigure 12.1, step 2 The neural plate invaginates, forming the neuralgroove, flanked by neural folds.2Neural foldsNeuralgrooveEmbryonic DevelopmentNeural groove fuses dorsally to form the neural tube Neural tube gives rise to the brain and spinal cord Figure 12.1, step 3 Neural fold cells migrate to form the neural crest,which will form much of the PNS and many otherstructures.3Neural crestFigure 12.1, step 4 The neural groove becomes the neural tube, whichwill form CNS structures.4SurfaceectodermHeadTailNeuraltubeEmbryonic DevelopmentAnterior end of the neural tube gives rise to three primary brain vesiclesProsencephalon—forebrainMesencephalon—midbrainRhombencephalon—hindbrain(a)Neuraltube(b) Primary brainvesiclesAnterior(rostral)Posterior(caudal)Rhombencephalon(hindbrain)Mesencephalon(midbrain)Prosencephalon(forebrain)Figure 12.2a-bEmbryonic DevelopmentPrimary vesicles give rise to five secondary brain vesiclesTelencephalon and diencephalon arise from the forebrainMesencephalon remains undividedMetencephalon and myelencephalon arise from the hindbrainEmbryonic DevelopmentTelencephalon  cerebrum (two hemispheres with cortex, white matter, and basal nuclei)Diencephalon  thalamus, hypothalamus, epithalamus, and retinaEmbryonic DevelopmentMesencephalon  brain stem (midbrain)Metencephalon  brain stem (pons) and cerebellumMyelencephalon  brain stem (medulla oblongata)Central canal of the neural tube enlarges to form fluid-filled ventricles(d) Adult brainstructures(c) Secondary brainvesiclesSpinal cordCerebellumBrain stem: medullaoblongataBrain stem: ponsBrain stem: midbrainDiencephalon(thalamus, hypothalamus,epithalamus), retinaCerebrum: cerebralhemispheres (cortex,white matter, basal nuclei)MyelencephalonMetencephalonMesencephalonDiencephalonTelencephalonCentral canalFourthventricle Cerebralaqueduct Third ventricleLateralventricles (e) Adultneural canalregionsFigure 12.2c-eEffect of Space Restriction on Brain DevelopmentMidbrain flexure and cervical flexure cause forebrain to move toward the brain stemCerebral hemispheres grow posteriorly and laterallyCerebral hemisphere surfaces crease and fold into convolutionsFigure 12.3aMetencephalonAnterior (rostral)Posterior (caudal)MesencephalonDiencephalonMidbrainCervicalSpinal cordFlexuresTelencephalonMyelencephalon(a) Week 5Figure 12.3bMidbrainCerebellumPonsMedulla oblongataSpinal cordCerebral hemisphereOutline of diencephalon(b) Week 13Figure 12.3cCerebellumPonsMedullaoblongata Spinal cordCerebralhemisphere(c) Week 26Regions and Organization of the CNSAdult brain regionsCerebral hemispheresDiencephalonBrain stem (midbrain, pons, and medulla)CerebellumFigure 12.3dCerebellumDiencephalonCerebralhemisphere(d) BirthBrain stem• Midbrain• Pons• Medullaoblongata Regions and Organization of the CNSSpinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tractsRegions and Organization of the CNSBrainSimilar pattern with additional areas of gray matterNuclei in cerebellum and cerebrumCortex of cerebellum and cerebrum Figure 12.4CerebrumCerebellumMigratorypattern ofneuronsCortex ofgray matterInner graymatterGray matterOuter whitematterCentral cavityCentral cavityInner gray matterGray matterOuter white matterCentral cavityInner gray matterOuter white matterRegion of cerebellumBrain stemSpinal cordVentricles of the BrainConnected to one another and to the central canal of the spinal cordLined by ependymal cellsVentricles of the BrainContain cerebrospinal fluidTwo C-shaped lateral ventricles in the cerebral hemispheresThird ventricle in the diencephalonFourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tubeFigure 12.5Anterior hornInterventricularforamenInferiorhornLateralaperture(b) Left lateral viewLateral ventricleSeptum pellucidumThird ventricleCerebral aqueduct(a) Anterior viewFourth ventricleCentral canalInferior hornPosteriorhornMedianapertureLateralapertureCerebral HemispheresSurface markingsRidges (gyri), shallow grooves (sulci), and deep grooves (fissures)Five lobesFrontalParietal Temporal OccipitalInsulaCerebral HemispheresSurface markingsCentral sulcusSeparates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobeLongitudinal fissureSeparates the two hemispheresTransverse cerebral fissureSeparates the cerebrum and the cerebellum PLAYAnimation: Rotatable brainFigure 12.6aPostcentralgyrusCentralsulcusPrecentralgyrusFrontallobe (a)Parietal lobeParieto-occipital sulcus(on medial surfaceof hemisphere)Lateral sulcusTransverse cerebral fissureOccipital lobeTemporal lobeCerebellumPonsMedulla oblongataSpinal cordCortex (gray matter)Fissure(a deepsulcus)GyrusSulcusWhite matterFigure 12.6bCentralsulcus(b)Frontal lobeTemporal lobe(pulled down)Gyri of insulaFigure 12.6cParietallobe Frontal lobeRight cerebralhemisphereOccipitallobeLeft cerebralhemisphereCerebral veinsand arteriescovered byarachnoidmaterLongitudinalfissurePosterior(c)AnteriorFigure 12.6dLeft cerebralhemisphereTransversecerebralfissureCerebellumBrain stem(d)Cerebral CortexThin (2–4 mm) superficial layer of gray matter40% of the mass of the brainSite of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understandingEach hemisphere connects to contralateral side of the bodyThere is lateralization of cortical function in the hemispheresFunctional Areas of the Cerebral CortexThe three types of functional areas are:Motor areas—control voluntary movementSensory areas—conscious awareness of sensationAssociation areas—integrate diverse informationConscious behavior involves the entire cortexMotor AreasPrimary (somatic) motor cortexPremotor cortexBroca’s areaFrontal eye fieldFigure 12.8aGustatory cortex(in insula)Primary motor cortexPremotor cortexFrontal eye fieldWorking memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks Broca’s area(outlined by dashes)Solving complex,multitask problems(a) Lateral view, left cerebral hemisphereMotor areasPrefrontal cortexSensory areas and relatedassociation areasCentral sulcusPrimary somatosensorycortexSomatosensoryassociation cortexSomaticsensation TasteWernicke’s area(outlined by dashes)Primary visualcortexVisualassociation areaVisionAuditoryassociation areaPrimaryauditory cortex HearingPrimary motor cortexMotor association cortexPrimary sensory cortexSensory association cortexMultimodal association cortexPrimary Motor CortexLarge pyramidal cells of the precentral gyriLong axons  pyramidal (corticospinal) tracts Allows conscious control of precise, skilled, voluntary movementsMotor homunculi: upside-down caricatures representing the motor innervation of body regionsFigure 12.9ToesSwallowingTongueJawPrimary motorcortex(precentral gyrus)MotorMotor map inprecentral gyrusPosteriorAnteriorPremotor CortexAnterior to the precentral gyrusControls learned, repetitious, or patterned motor skillsCoordinates simultaneous or sequential actions Involved in the planning of movements that depend on sensory feedbackBroca’s AreaAnterior to the inferior region of the premotor areaPresent in one hemisphere (usually the left)A motor speech area that directs muscles of the tongueIs active as one prepares to speakFrontal Eye FieldAnterior to the premotor cortex and superior to Broca’s areaControls voluntary eye movementsSensory AreasPrimary somatosensory cortexSomatosensory association cortexVisual areasAuditory areas Olfactory cortexGustatory cortexVisceral sensory areaVestibular cortexFigure 12.8aGustatory cortex(in insula)Primary motor cortexPremotor cortexFrontal eye fieldWorking memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks Broca’s area(outlined by dashes)Solving complex,multitask problems(a) Lateral view, left cerebral hemisphereMotor areasPrefrontal cortexSensory areas and relatedassociation areasCentral sulcusPrimary somatosensorycortexSomatosensoryassociation cortexSomaticsensation TasteWernicke’s area(outlined by dashes)Primary visualcortexVisualassociation areaVisionAuditoryassociation areaPrimaryauditory cortex HearingPrimary motor cortexMotor association cortexPrimary sensory cortexSensory association cortexMultimodal association cortexPrimary Somatosensory CortexIn the postcentral gyriReceives sensory information from the skin, skeletal muscles, and jointsCapable of spatial discrimination: identification of body region being stimulatedFigure 12.9GenitalsIntra-abdominalPrimary somato-sensory cortex(postcentral gyrus)SensorySensory map inpostcentral gyrusPosteriorAnteriorSomatosensory Association CortexPosterior to the primary somatosensory cortexIntegrates sensory input from primary somatosensory cortexDetermines size, texture, and relationship of parts of objects being feltVisual AreasPrimary visual (striate) cortexExtreme posterior tip of the occipital lobeMost of it is buried in the calcarine sulcusReceives visual information from the retinasVisual AreasVisual association areaSurrounds the primary visual cortexUses past visual experiences to interpret visual stimuli (e.g., color, form, and movement)Complex processing involves entire posterior half of the hemispheresAuditory AreasPrimary auditory cortexSuperior margin of the temporal lobesInterprets information from inner ear as pitch, loudness, and locationAuditory association areaLocated posterior to the primary auditory cortexStores memories of sounds and permits perception of soundsOIfactory CortexMedial aspect of temporal lobes (in piriform lobes)Part of the primitive rhinencephalon, along with the olfactory bulbs and tracts(Remainder of the rhinencephalon in humans is part of the limbic system)Region of conscious awareness of odorsGustatory CortexIn the insulaInvolved in the perception of tasteVisceral Sensory AreaPosterior to gustatory cortexConscious perception of visceral sensations, e.g., upset stomach or full bladderVestibular CortexPosterior part of the insula and adjacent parietal cortexResponsible for conscious awareness of balance (position of the head in space)Figure 12.8aGustatory cortex(in insula)Primary motor cortexPremotor cortexFrontal eye fieldWorking memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks Broca’s area(outlined by dashes)Solving complex,multitask problems(a) Lateral view, left cerebral hemisphereMotor areasPrefrontal cortexSensory areas and relatedassociation areasCentral sulcusPrimary somatosensorycortexSomatosensoryassociation cortexSomaticsensation TasteWernicke’s area(outlined by dashes)Primary visualcortexVisualassociation areaVisionAuditoryassociation areaPrimaryauditory cortex HearingPrimary motor cortexMotor association cortexPrimary sensory cortexSensory association cortexMultimodal association cortexFigure 12.8bFrontal eye fieldPrefrontalcortexProcesses emotionsrelated to personaland social interactions(b) Parasagittal view, right hemisphereOlfactory bulbOrbitofrontalcortexOlfactory tractFornixTemporal lobeCorpuscallosumPremotor cortexPrimarymotor cortexCingulategyrusCentral sulcusPrimary somatosensorycortexParietal lobeParieto-occipitalsulcusSomatosensoryassociation cortexOccipitallobeVisualassociationareaCalcarine sulcusParahippocampalgyrusUncusPrimaryolfactory cortexPrimaryvisual cortexPrimary motor cortexMotor association cortexPrimary sensory cortexSensory association cortexMultimodal association cortexMultimodal Association AreasReceive inputs from multiple sensory areasSend outputs to multiple areas, including the premotor cortexAllow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to takeMultimodal Association AreasThree partsAnterior association area (prefrontal cortex)Posterior association areaLimbic association areaAnterior Association Area (Prefrontal Cortex)Most complicated cortical regionInvolved with intellect, cognition, recall, and personalityContains working memory needed for judgment, reasoning, persistence, and conscienceDevelopment depends on feedback from social environmentPosterior Association AreaLarge region in temporal, parietal, and occipital lobesPlays a role in recognizing patterns and faces and localizing us in spaceInvolved in understanding written and spoken language (Wernicke’s area)Limbic Association AreaPart of the limbic systemProvides emotional impact that helps establish memories