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Functional Systems in the CNS

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Functional Systems in the CNS FunctionalFunctional systemssystems inin CNSCNS GeneralGeneral featuresfeatures NervousNervous system:system: stimulusstimulus andand reactionreaction environment organism Nervous system stimulus reaction sensory inter - motor receptor effector neuron neuron neuron Functional systems in the CNS SensorySensory (afferent)(afferent) systemssystems MotorMotor (efferent)(efferent) systemssystems LimbicLimbic systemsystem ReticularReticular systemsystem CentralCentral transmittertransmitter systemssystems cholinergic system monoaminergic system amino acid transmitters peptidergic system central neuroendocrine system SensorySensory systemssystems –– basicbasic conceptsconcepts ModalityModality ofof SensationSensation ReceptorReceptor SensorySensory TractTract primaryprimary neuronneuron secondarysecondary neuronneuron tertiarytertiary neuronneuron terminationtermination ReceptorsReceptors ofof sensorysensory systemssystems -- primaryprimary sensorysensory neuronsneurons The distal ending of the primary afferents is the receptor A special receptor cell conveys to primary afferents ReceptorsReceptors ofof sensorysensory systemssystems -- primaryprimary sensorysensory neuronsneurons pseudounipolar part of PNS (except jaw proprioception) bipolar part of CNS Sensory (afferent) systems GGeneraleneral (somatic)(somatic) sensationssensations –– somatosensorysomatosensory systemssystems superficial (exteroceptive) – skin : pain and temperature vibration, touch and pressure stereognosia deep (proprioceptive) - joints and tendons interoceptive (visceroceptive) - organs and blood vessels SSpecialpecial sensationssensations visual system vestibulocochlear system gustatory system olfactory system ClinicalClinical casecase AA 2121 yryr oldold malemale isis seenseen weavingweaving hishis motorcyclemotorcycle inin andand outout ofof traffic.traffic. Unfortunately,Unfortunately, hehe spinsspins outout andand smashessmashes hishis lowerlower backback againstagainst thethe curbcurb SeveralSeveral monthsmonths afterafter thethe accident,accident, thethe malemale hashas lossloss ofof discriminativediscriminative touch,touch, vibrationvibration andand proprioceptionproprioception inin oneone legleg andand painpain andand temperaturetemperature sensationsensation inin thethe otherother legleg ExplainExplain thethe findings!findings! SomaticSomatic sensorysensory systemsystem SystemSystem forfor detectingdetecting light touch vibration pressure cutaneous tension SystemSystem forfor detectingdetecting painful stimuli temperature MechanosensoryMechanosensory systemsystem -- componentscomponents CutaneousCutaneous MechanoreceptorsMechanoreceptors && ProprioceptorsProprioceptors AscendingAscending pathwayspathways PrimaryPrimary somaticsomatic sensorysensory cortexcortex HigherHigher --orderorder associationassociation corticescortices Cutaneous and subcutaneous mechanoreceptors ByBy functionfunction mechanoreceptorsmechanoreceptors nociceptorsnociceptors thermoceptorsthermoceptors ByBy morphologymorphology freefree (mainly(mainly nocinoci -- && thermoceptors)thermoceptors) encapsulatedencapsulated FlowFlow ofof informationinformation SkinSkin stimulistimuli deformdeform thethe receptorsreceptors IonicIonic permeabilitypermeability ofof thethe receptorreceptor cellcell membranemembrane isis alteredaltered ChangesChanges inin permeabilitypermeability generategenerate aa depolarizingdepolarizing currentcurrent ReceptorReceptor potentialspotentials triggertrigger actionaction potentialpotential What? Where? qualityquality aa stimulusstimulus -- propertiesproperties ofof thethe receptorreceptor Strength quantityquantity aa stimulusstimulus -- firingfiring raterate ofof actionaction potentialspotentials Somatosensation - receptors Glabrous skin epidermis dermis Mechanoreceptors Thermoreceptors, Nociceptors Somatosensation - receptors Glabrous skin reading Braille epidermis 30-50 Hz “texture” dermis Meissner’s Corpuscles – Rapidly adapting MeissnerMeissner ’’ss corpusclecorpuscle Somatosensation - receptors Glabrous skin epidermis dermis Pacinian Corpuscles – Rapidly adapting 250-300 Hz – “vibration/tickle” VaterVater --PacinianPacinian (( PacinianPacinian )) CorpuscleCorpuscle inner core of membrane lamellae → fluid → outer lamella Somatosensation - receptors Glabrous skin epidermis dermis Merkel’s Disks – Slowly adapting Static or low frequency light pressure Somatosensation - receptors Glabrous skin epidermis dermis Ruffini’s Corpuscles – Slowly adapting Static/directional stretch of skin RuffiniRuffini ’’ss endingending Somatosensation - receptors Glabrous skin epidermis dermis Free nerve endings – Pain/temperature SomatosensorySomatosensory systemsystem ReceptorsReceptors –– SmallSmall fibersfibers ThermoreceptionThermoreception –– ““barebare endingsendings ”” warmwarm coldcold NociceptionNociception –– ““barebare endingsendings ”” nociceptornociceptor –– mechanical,mechanical, thermalthermal polymodalpolymodal –– mechanical,mechanical, thermal,thermal, chemicalchemical Skin mechanoreceptors (low-threshold = high sensitivity) Meissner ’s corpuscles most abundant mechanoreceptors of hairless skin (40% of hand) connective tissue capsule + Schwann cell lamellae low -frequency vibrations (30 –50 Hz) – rough objects Pacinian corpuscles less frequent (20% of hand) inner core of membrane lamellae → fluid → outer lamella high -frequency vibrations (250 –350 Hz) → fine textures Merkel ’s disks epidermal (20% of hand) light pressure - discrimination of shapes, edges Ruffini ’s corpuscles deep in the skin + in ligaments & tendons sensitive to the cutaneous stretching produced by digit or limb movements Purves, et al, Neuroscience, 3rd ed. Receptive fields & adaptation epidermis dermis rapidly-adapting slowly-adapting rapidly-adapting slowly-adapting Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Differences in mechanosensory discrimination across the body surface → receptor density Purves, et al, Neuroscience, 3rd ed. Dermatome - the area of skin innervated by a single dorsal root Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Afferent pathways for mechanosensory information TheThe dorsaldorsal columncolumn ––medialmedial lemniscuslemniscus (DC(DC --ML)ML) pathwaypathway →→ touchtouch && proprioceptionproprioception SpinothalamicSpinothalamic (( anterolateralanterolateral ,, AL)AL) pathwaypathway →→ painpain && temperaturetemperature TrigeminothalamicTrigeminothalamic tractstracts TwoTwo somatosensorysomatosensory pathwayspathways SomatosensorySomatosensory systemsystem –– generalgeneral featuresfeatures ofof pathwayspathways CommonCommon featurefeature ofof twotwo pathwayspathways 33--neuronalneuronal systemssystems firstfirst --orderorder afferentafferent fiberfiber secondsecond --orderorder neuronneuron projectingprojecting toto contralateralcontralateral thalamusthalamus thirdthird --orderorder neuronneuron projectingprojecting toto SS --II (S1)(S1) cortexcortex TopographicTopographic (somatotopic)(somatotopic) organizationorganization 11st --orderorder neuronneuron forfor somatosensorysomatosensory pathwayspathways central process cell body in DRG peripheral process DRGDRG (dorsal(dorsal rootroot ganglion)ganglion) neuronneuron pseudounipolar cell telodendron DorsalDorsal ColumColum --MedialMedial LemniscalLemniscal (DC(DC --ML)ML) PathwayPathway Modality:Modality: DiscriminativeDiscriminative Touch Touch Sensation Sensation (include (include Vibration) Vibration) and and ConsciousConscious Proprioception Proprioception (Position (Position Sensa Sensation,tion, Kinesthesia) Kinesthesia) fromfrom body body Receptor:Receptor: Most Most receptors receptors except except free free nerve nerve endings endings 11stst Neuron:Neuron: Dorsal Dorsal Root Root Ganglion Ganglion DorsalDorsal column column (spinal (spinal white white matter) matter) 22ndnd Neuron:Neuron: Dorsal Dorsal Column Column Nuclei Nuclei(Nucleus (Nucleus Gracilis Gracilis et et Cuneatus) Cuneatus) InternalInternal arcuate arcuatefiber fiber - -Lemniscal Lemniscal decussation decussation - -Medial Media llemniscus lemniscus 33rdrd Neuron:Neuron: Thalamus Thalamus (VPLc) (VPLc) InternalInternal capsule capsule ----- -----Corona Corona radiata radiata Termination:Termination: Primary Primary Somesthetic Somesthetic Area Area (S (S I) I) TouchTouch andand ProprioceptionProprioception DorsalDorsal Column/MedialColumn/Medial LemniscusLemniscus pathwaypathway ModalitiesModalities lightlight touchtouch vibrationvibration proprioceptionproprioception Touch and Proprioception Dorsal Columns /Medial Lemniscal System Fasiculus cuneatus Fasiculus gracilis (upper body) (lower body) Origin: Dorsal root ganglion (cervical or lumbar) Course: Fasiculus gracilis/cuneatus Neuron #1 Termination: Nucleus cuneatus (upper body) Nucleus gracilis (lower body) Laterality: IPSI Touch and Proprioception Dorsal Columns /Medial Lemniscal System Fasiculus cuneatus Fasiculus gracilis (upper body) (lower body) Origin: Dorsal root ganglion (cervical or lumbar) Course: Fasiculus gracilis/cuneatus Neuron #1 Termination: Nucleus cuneatus (upper body) Nucleus gracilis (lower body) Laterality: IPSI Touch and Proprioception Dorsal Columns/ Medial Lemniscal System Nucleus gracilis Nucleus cuneatus Internal Arcuate Fibers Medial Lemniscus Origin: Nucleus gracilis/cuneatus Course: Medial Lemniscus Neuron #2 Termination: VPL of Thalamus Laterality: CONTRA Touch and Proprioception Dorsal Columns/ Medial Lemniscal System
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