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)

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

Nucleus gracilis

Nucleus cuneatus

Internal Arcuate Fibers

Medial Lemniscus

Fibers from the nuclei form the internal arcuate fibers , which decussate and form the medial lemniscus Touch and Proprioception Dorsal Columns/ Medial Lemniscal System

Medial Lemniscus

Note: Head not represented in the ML

Origin: Nucleus gracilis/cuneatus Cuneatus Course: Medial Lemniscus Neuron #2 Termination: VPL of Thalamus

Laterality: CONTRA Gracilis Touch and Proprioception Dorsal Columns/ Medial Lemniscal System

Origin: Nucleus gracilis/cuneatus Course: Medial Lemniscus Neuron #2 Termination: VPL of Thalamus Laterality: CONTRA Touch and Proprioception Dorsal Columns/ Medial Lemniscal System

Origin: Nucleus gracilis/cuneatus Neuron #2 Course: Medial Lemniscus Termination: VPL of Thalamus Laterality: CONTRA Touch and Proprioception Dorsal Columns/ Medial Lemniscal System

Origin: Nucleus gracilis/cuneatus Course: Medial Lemniscus Neuron #2 Termination: VPL of Thalamus Laterality: CONTRA Touch and Proprioception Dorsal Columns/ Medial Lemniscal System To primary somatosensory VPL cortex Nucleus of Thalamus

Origin: Nucleus gracilis/cuneatus Course: Medial Lemniscus Neuron #2 Termination: VPL of Thalamus Laterality: CONTRA Touch and Proprioception Dorsal Columns/ Medial Lemniscal System L T A F

Origin: VPL of Thalamus Course: Posterior Limb Internal Capsule Neuron #3 Termination: Primary Somatosensory Cortex (BA3,1,2) Laterality: IPSI D DCDC --MLML PathwayPathway

DRG: Dorsal Root Ganglion 1. Posterior White Column A. Nucleus gracilis B. Nucleus cuneatus 2. Medial Lemniscus 3. Corona Radiata DRG C. Thalamus (VPLc) D. Cerebral Cortex (S I) SpinothalamicSpinothalamic tracttract (AL(AL system)system)

Modality:Modality: PainPain & & Temperature Temperature Sensation, Sensation, LightLight Touch Touch from from body body Receptor:Receptor: Free Free Nerve Nerve Ending Ending 11stst Neuron:Neuron: DorsalDorsal RootRoot GanglionGanglion nd 22nd Neuron:Neuron: DorsalDorsal HornHorn (Lamina(Lamina I, I, IV, IV, V) V) AnteriorAnterior white white commissure commissure SpinothalamicSpinothalamic tract tract (Spinal (Spinal Lemniscus) Lemniscus) 33rdrd Neuron:Neuron: ThalamusThalamus (VPLc(VPLc && CL)CL) InternalInternal capsule capsule ------Corona Corona radiata radiata Termination:Termination: PrimaryPrimary SomestheticSomesthetic AreaArea (S(S I)I) PainPain andand TemperatureTemperature

AnterolateralAnterolateral (Ventrolateral)(Ventrolateral) SystemSystem ((=SpinothalamicSpinothalamic tract)tract) ModalitiesModalities painpain temperaturetemperature Pain and Temperature (Anterolateral system) Substantia gelatinosa

Small diameter primary afferent fiber

Origin: DRG Neuron #1 Course: Dorsal root Termination: Substantia gelatinosa Laterality: IPSI Pain and Temperature (Anterolateral system) Spinothalamic Tract

Ventral White Commissure

Origin: Lamina I or V Course: Ventral White Commissure, Neuron #2 Spinothalamic Tract Termination: VPL of the Thalamus Laterality: CONTRA Pain and Temperature (Anterolateral system) Spinothalamic Tract

Origin: VPL Thalamus Course: Posterior Limb of Internal Capsule Neuron #3 Termination: Primary Somatosensory Cortex (BA 3,1,2) Laterality: IPSI Pain and Temperature (Anterolateral system)

L T A F

Origin: VPL Thalamus Neuron #3 Course: Posterior Limb of Internal Capsule Termination: Primary Somatosensory Cortex (BA 3,1,2) Laterality: IPSI D SpinothalamicSpinothalamic tracttract ALAL SystemSystem

DRG: Dorsal Root Ganglion A. Spinal Dorsal Horn B. Reticular Formation 1. Neospinothalamic Tract 2. Paleospinothalamic Tract C. Thalamus (VPLc, CL) 3. Corona Radiata DRG D. Cerebral Cortex (S I) ALAL systemsystem

AdditionalAdditional ALAL systemsystem pathways:pathways: Spinoreticular → RAS (awaking in response to pain stimuli) Spinomesencephalic → periaqueductal gray (pain control) Spinotectal → superior colliculus (turning the upper body, head, and eyes in the direction of a painful stimulus ) Spinohypothalamic – autonomic response to nociception DC-ML vs AL systems

Variable DC-ML Pathway AL Pathway Course in spinal Dorsal and dorsolateral funiculi Ventral and ventrolateral funiculi cord Size of receptive Small Small and large fields Specificity of signal Each sensation carried separately; Multimodal (several sensations conveyed precise localization of sensation carried in one fiber system) Diameter of nerve Large-diameter primary afferents Small-diameter primary afferents fiber Sensation Fine touch, joint sensation, vibration Pain, temperature, crude touch, transmitted visceral pain Synaptic chain Two or three synapses to cortex Multisynaptic

Speed of Fast Slow transmission Tests for function Vibration, two-point discrimination, Pinprick, heat and cold testing stereognosis FaceFace innervationinnervation →→ CNCN VV TrigeminalTrigeminal systemsystem -- TrigeminothalamicTrigeminothalamic tractstracts

Modality:Modality: GeneralGeneral Sensation Sensation fromfrom face face Receptor:Receptor: Most Most receptors receptors in in the the face face

11stst Neuron:Neuron: TrigeminalTrigeminal ( (semilunar)semilunar ) gangliaganglia 22ndnd Neuron:Neuron: TrigeminalTrigeminal sensorysensory nucleusnucleus (principal)(principal) painpain & & temperature temperature------Spinal Spinal trigeminal trigeminal nucleus nucleus VentralVentral and and Dorsal Dorsal trigeminothalamic trigeminothalamic tracts tracts 33rdrd Neuron:Neuron: ThalamusThalamus (VPM)(VPM) InternalInternal capsule capsule ------Corona Corona radiata radiata Termination:Termination: PrimaryPrimary SomestheticSomesthetic AreaArea (S(S I)I) Trigeminothalamic Tracts

A. trigeminal ganglion B. trigeminal sensory nucleus Dorsal TTT C. thalamus (VPM) Ventral TTT (ipsilateral) (contralateral) D. cerebral cortex (S I) 1. spinal tract of trigeminal nerve 2. ventral trigeminothalamic tract 3. dorsal trigeminothalamic tract 4. corona radiata V. trigeminal nerve

The bilateral representation in VPM (contralateral VTTT & ipsilateral DTTT), reflects the function of oral structures on each side, which typically work together during behaviors such as chewing or talking SummarySummary ofof trigeminaltrigeminal sensorysensory nucleinuclei

Mesencephalic Mechanoreceptive afferent fibers → principal sensory nucleus Trigeminal Pain & temperature → spinal Principal trigeminal nucleus Proprioceptive afferent fibers (jaw muscles ) → mesencephalic trigeminal nucleus (the only primary sensory neurons with Spinal cell bodies located in CNS!!!) JawJaw jerkjerk reflexreflex –– CNCN VV

Proprioceptive fibers to the mesencephalic nucleus convey pressu re and kinesthesia from the teeth, periodontium, hard palate, and joint capsules as well as impulses from stretch receptors in the muscles of mastication. T he mesencephalic nucleus is concerned with mechanisms that control the force of t he bite. CNCN V:V: TrigeminalTrigeminal -- mesencephalicmesencephalic

The mesencephalic nucleus and tract run above the level of CN V

Origin: Mesencephalic Nucleus of V Course: Mesencephalic tract of V Termination: Motor Nucleus of V Laterality: Bilateral CNCN V:V: TrigeminalTrigeminal -- mesencephalicmesencephalic The mesencephalic nucleus and tract run Origin: Mesencephalic above the level of CN V Nucleus of V Course: Mesencephalic tract of V Termination: Motor Nucleus of V Laterality: Bilateral CNCN V:V: TrigeminalTrigeminal -- mesencephalicmesencephalic

The mesencephalic Origin: Mesencephalic nucleus and tract run Nucleus of V above the level of CN V Course: Mesencephalic tract of V Termination: Motor Nucleus of V Laterality: Bilateral CNCN V:V: TrigeminalTrigeminal motormotor andand principalprincipal sensorysensory nucleinuclei (level(level ofof CNCN V)V)

Chief Sensory Motor nucleus nucleus of V of V

R A L L A A S A B CNCN V:V: TrigeminalTrigeminal SpinalSpinal nucleusnucleus andand tracttract atat levellevel ofof VI/VIIVI/VII

Neuron #1 Origin: Trigeminal (Gasserian) Ganglion Course: All branches of Trigeminal Nerve, Spinal Trigeminal tract Termination: Spinal Nucleus of V Laterality: Ipsilateral CNCN V:V: TrigeminalTrigeminal SpinalSpinal nucleusnucleus andand tracttract atat levellevel ofof XX

Neuron #1 Origin: Trigeminal (Gasserian) Ganglion Course: All branches of Trigeminal Nerve, Spinal Trigeminal tract Termination: Spinal Nucleus of V Laterality: Ipsilateral Neuron #2 Origin: Spinal Nucleus CNCN V:V: VTTTVTTT of V Medial Course: VTTT, with lemniscus Medial Lemniscus Termination: VPM Thalamus VTTT Laterality: Contralateral

Caudal medulla VTTT Ventral Trigeminothalamic Tract (trigeminal lemniscus)

Medial lemniscus Rostral medulla Neuron #2 Origin: Spinal Nucleus CNCN V:V: VTTTVTTT of V and Chief Sensory Nuc. Course: VTTT, with Medial Lemniscus Termination: VPM VTTT Thalamus Laterality: Contralateral

VTTT

Medial lemniscus Caudal pons Ventral Trigeminothalamic Tract (trigeminal lemniscus) Medial lemniscus Rostral pons Neuron #2 CN V: VTTT Origin: Spinal Nucleus CN V: VTTT of V and Chief Sensory Nuc. Course: VTTT, with Medial Lemniscus Termination: VPM Thalamus Laterality: Contralateral TrigeminalTrigeminal pathwayspathways arrivearrive atat VPMVPM

Ventral Posteromedial (VPM) Nucleus

Thalamus TrigeminalTrigeminal NeuralgiaNeuralgia (tic(tic douloureux)douloureux) - excruciating episodic pain in the area supplied by trigeminal nerve, especially second and third division - trigger point - intense pain makes the patient grimace (tic) - antiepileptic drug (phenytoin , carbamazepine ) is effective - surgical treatment HerpesHerpes ZosterZoster (Shingles)(Shingles) Zoster ophthalmicus

Varicella -zoster virus reactivation from the dorsal root ganglia Unilateral vesicular eruption within a dermatome OOrganizationrganization ofof somatosensorysomatosensory pathwayspathways

Upper-level decussation

Lower-level decussation 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 ExplanationExplanation →→ BrownBrown --SSééquardquard syndromesyndrome Brown-Séquard syndrome

DC -ML system – ipsilateral damage AL system – contralateral damage

lesion

(DC-ML system)

(AL system) FastFast && SlowSlow PainPain ALAL systemsystem carriescarries bothboth fastfast andand slowslow painpain

Fast Pain Slow Pain

Sharp, pricking Dull, burning Group III (A δδδ) fiber Group IV (C) fiber Short latency Slower onset Well localized Diffuse Short duration Long duration Less emotional Emotional, autonomic response Not blocked by morphine Blocked by morphine Neospinothalamic tract Paleospinothalamic tract NeoSTT PaleoSTT

Primary Motor Widespread Area (M I) cortical region

VPLc ( ventrobasal CL ( intralaminar nuclear complex) thalamic nuclei) thalamus

(spinal lemniscus) reticulothalamic pathways spinothalamic spinoreticular tract tract reticular formation

Spinothalamic Tract & Spinoreticular Tract Spinothalamic pain pathways

Neospinothalamic Somato- Lateral sensory Sensation thalamus Spinal Paleospinothalamic cortex Cord

Reticular Medial Association Affect Formation thalamus cortex Nociceptive afferent fibers terminate on projection neurons in the dorsal horn of the spinal cord

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Descending systems modulate the transmission of ascending pain signals

Purves, et al, Neuroscience, 3rd ed. Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Descending analgesic pathways activate enkephalin- containing local circuit neurons

SER, NA

Glu, NP

Purves, et al, Neuroscience, 3rd ed. Endogenous opioid peptides arise from three large precursor polyproteins

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. AnalgesiaAnalgesia -- enkephalinenkephalin && morphinemorphine

opium Sensory input Sensory input + opiates/opioids

morphine

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. VisceroceptiveVisceroceptive pathwayspathways (mainly(mainly nociceptive)nociceptive)

Conventional visceroceptive pathway 1st neuron – spinal ganglion 2nd neuron – intermediomedial column of spinal gray matter → lateral spinothalamic tract 3rd neuron – VPL (thalamus) → somatosensory cortical areas Accessory visceroceptive pathway: 1st neuron – CN IX & X 2nd neuron – solitary nucleus 3rd neuron – VPL (thalamus) Signals from nociceptors in the viscera can be felt as pain elsewhere in the body

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Examples of referred pain

Purves, et al, Neuroscience, 3rd ed. PrimaryPrimary somatosensorysomatosensory cortexcortex (S(S --I,I, S1)S1)

(red) SomatosensorySomatosensory homunculushomunculus

Somatotopic mapping

Homunculus is based on peripheral receptor density → greatest area to fingers, lips EachEach ofof thethe fourfour areasareas ofof thethe primaryprimary somaticsomatic sensosensoryry cortexcortex (3a,(3a, 3b,3b, 1,1, andand 2)2) receivesreceives inputinput fromfrom allall aareasreas ofof thethe bodybody surface,surface, butbut oneone modalitymodality tendstends toto dominatdominatee inin eacheach areaarea

3a - from proprioceptors signaling muscle stretch 3b & 1 - from cutaneous mechanoreceptors 2 – from both tactile and proprioceptive stimuli The receptive fields of neurons in the primary somatic sensory cortex are larger than those of the sensory afferents

area 2 neuron is directionally sensitive to motion toward the fingertips

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Organization of S-I

Layer 3 S-II Layer 4 Contralateral S-I Layer 5

Thalamus

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Connections between cortical areas represent stages of information processing. At each stage progressively more abstract information is extracted from the sensory stimulus.

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. Ascending sensory pathways

Spinocerebellar tracts → unconcious proprioception SpinocerebellarSpinocerebellar tractstracts (SCbT)(SCbT)

Modality: Unconscious Proprioception Receptor: Muscle spindle, Golgi tendon organ

1st Neuron: Dorsal Root Ganglion Posterior Root , [Posterior Column] 2nd Neuron: 1. Clarke ’s column Posterior SCbT 2. Accessory Cuneate Nucleus Cuneocerebellar tract 3. Posterior Horn Anterior SCbT Termination: Cerebellar Cortex MMuscleuscle spindlespindle ss

Capsule IIntrafusalntrafusal musclemuscle fibersfibers CConnectiveonnective tissuetissue capsulecapsule Extrafusal fiber

Intrafusal Extrafusal fibers fiber

Extrafusal fiber GolgiGolgi tendontendon organsorgans

CollagenousCollagenous fibersfibers parallelparallel toto thethe extrafusalextrafusal musclemuscle fibersfibers UUnmyelinatednmyelinated nervenerve terminalsterminals CConnectiveonnective tissuetissue capsulecapsule PPosteriorosterior SCbTSCbT && cuneocerebellarcuneocerebellar tracttract -- ipsilateralipsilateral

Cuneocerebellar tract

(ICP)

Information about phase, rate, and strength of muscle contraction

Posterior SCbT PosteriorPosterior (Dorsal)(Dorsal) SCbTSCbT

Origin: Clarke’s Column, T1-L2 Course: Dorsolateral spinal cord and medulla, enters the cerebellum thru ICP Termination: granule cells of the vermis and intermediate zone Laterality: Ipsilateral PosteriorPosterior (Dorsal)(Dorsal) SCbTSCbT

(SCP)

Information related to interneuronal activity and the effectiveness of descending pathways

laminae V-VII AnteriorAnterior vsvs PosteriorPosterior SCbTSCbT

Anterior SCbT Posterior SCbT

SCP ICP anterior post. SCbT and spinocerebellar cuneocerebellar tract tract anterior white posterior commissure white column posterior root posterior root FriedreichFriedreich ’’ss AtaxiaAtaxia

posterior spinocerebellar tract lesion - cerebellar ataxia

Patients tend to walk with a wide base, stagger, and frequently fall FromFrom sensingsensing toto respondingresponding

Motoneuron DRG