Functional systems in CNS

Functional systems in CNSFunctional systems in CNS

General featuresGeneral features

Nervous systemNervous system

sensory sensory

neuronneuron

stimulusstimulus reactionreaction

effectoreffectorinterinter--

neuronneuronreceptorreceptor

motormotor

neuronneuron

organismorganism

Nervous system: stimulus and reactionNervous system: stimulus and reaction

environmentenvironment

Functional systems in the CNS

�� Sensory (afferent) systemsSensory (afferent) systems

�� Motor (efferent) systemsMotor (efferent) systems

�� Limbic systemLimbic system

�� Reticular systemReticular system

�� Central transmitter systemsCentral transmitter systems�� cholinergic systemcholinergic system

�� monoaminergic systemmonoaminergic system

�� amino acid transmittersamino acid transmitters

�� peptidergic systempeptidergic system

�� central neuroendocrine systemcentral neuroendocrine system

Sensory systems Sensory systems –– basic conceptsbasic concepts

�� Modality of SensationModality of Sensation

�� ReceptorReceptor

�� Sensory TractSensory Tract

�� primary neuronprimary neuron

�� secondary neuronsecondary neuron

�� tertiary neurontertiary neuron

�� terminationtermination

Receptors of sensory systems Receptors of sensory systems -- primary primary

sensory neurons sensory neurons

TThe he distal endingdistal ending of theof the

primary afferents is the receptorprimary afferents is the receptor

A A special receptor cellspecial receptor cell

conveys to primary afferentsconveys to primary afferents

Receptors of sensory systems Receptors of sensory systems -- primary primary

sensory neurons sensory neurons

pseudounipolarpseudounipolar

bipolarbipolar

part of CNSpart of CNS

part of PNS part of PNS

(except jaw (except jaw

proprioception)proprioception)

Sensory (afferent) systems

�� GGeneral (somatic) sensationseneral (somatic) sensations –– somatosensory systemssomatosensory systems�� superficial (exteroceptive) superficial (exteroceptive) –– skin :skin :

�� pain and temperaturepain and temperature

�� vibration, touch and pressurevibration, touch and pressure

�� stereognosiastereognosia

�� deep (proprioceptive)deep (proprioceptive) -- joints and tendonsjoints and tendons

�� interoceptive (visceroceptive)interoceptive (visceroceptive) -- organs and blood vesselsorgans and blood vessels

�� SSpecial sensationspecial sensations�� visual systemvisual system

�� vestibulocochlear systemvestibulocochlear system

�� gustatory systemgustatory system

�� olfactory systemolfactory system

Clinical caseClinical case

�� A 21 yr old male is seen weaving his motorcycle in A 21 yr old male is seen weaving his motorcycle in and out of traffic. Unfortunately, he spins out and and out of traffic. Unfortunately, he spins out and smashes his lower back against the curbsmashes his lower back against the curb

�� Several months after the accident, the male has loss Several months after the accident, the male has loss of discriminative touch, vibration and of discriminative touch, vibration and proprioception in proprioception in oneone leg and pain and temperature leg and pain and temperature sensation in the sensation in the otherother legleg

�� Explain the findings! Explain the findings!

Somatic sensory systemSomatic sensory system

�� System for detectingSystem for detecting�� light touchlight touch

�� vibrationvibration

�� pressurepressure

�� cutaneous tensioncutaneous tension

�� System for detectingSystem for detecting�� painful stimulipainful stimuli

�� temperaturetemperature

�� Cutaneous Mechanoreceptors & Cutaneous Mechanoreceptors &

ProprioceptorsProprioceptors

�� Ascending pathwaysAscending pathways

�� Primary somatic sensory cortexPrimary somatic sensory cortex

�� HigherHigher--order association corticesorder association cortices

Mechanosensory system Mechanosensory system -- componentscomponents

Cutaneous and subcutaneous

mechanoreceptors

�� By functionBy function

�� mechanoreceptorsmechanoreceptors

�� nociceptorsnociceptors

�� thermoceptorsthermoceptors

�� By morphologyBy morphology

�� free (mainly nocifree (mainly noci-- & thermoceptors)& thermoceptors)

�� encapsulatedencapsulated

Flow of informationFlow of information

�� Skin stimuli deform the receptorsSkin stimuli deform the receptors

�� Ionic permeability of the receptor cell Ionic permeability of the receptor cell membrane is alteredmembrane is altered

�� Changes in permeability generate a Changes in permeability generate a depolarizing currentdepolarizing current

�� Receptor potentials trigger action potentialReceptor potentials trigger action potential

quality a stimulus quality a stimulus -- properties of the receptorproperties of the receptorWhat? Where?

quantity a stimulus quantity a stimulus -- firing rate of action potentialsfiring rate of action potentialsStrength

Somatosensation - receptors

epidermis

dermis

Glabrous skin

Mechanoreceptors Thermoreceptors,Nociceptors

epidermis

dermis

Glabrous skin

30-50 Hz“texture”

Meissner’s Corpuscles – Rapidly adapting

reading Braille

MeissnerMeissner’’s corpuscles corpuscle

epidermis

dermis

Glabrous skin

250-300 Hz – “vibration/tickle”Pacinian Corpuscles – Rapidly adapting

VaterVater--Pacinian (Pacinian (PacinianPacinian) Corpuscle) Corpuscle

inner core of membrane lamellae inner core of membrane lamellae →→ fluid fluid →→ outer lamellaouter lamella

epidermis

dermis

Glabrous skin

Static or low frequency light pressureMerkel’s Disks – Slowly adapting

epidermis

dermis

Glabrous skin

Static/directional stretch of skinRuffini’s Corpuscles – Slowly adapting

RuffiniRuffini’’s endings ending

epidermis

dermis

Glabrous skin

Free nerve endings – Pain/temperature

Somatosensory systemSomatosensory system

�� Receptors Receptors –– Small fibersSmall fibers

�� Thermoreception Thermoreception –– ““bare endingsbare endings””

�� warmwarm

�� coldcold

�� Nociception Nociception –– ““bare endingsbare endings””

�� nociceptornociceptor –– mechanical, thermalmechanical, thermal

�� polymodalpolymodal –– mechanical, thermal, chemicalmechanical, thermal, chemical

Skin mechanoreceptors(low-threshold = high sensitivity)

�� MeissnerMeissner’’s corpuscless corpuscles�� most abundant mechanoreceptors of hairless skin (40% of hand)most abundant mechanoreceptors of hairless skin (40% of hand)

�� connective tissue capsule + Schwann cell lamellaeconnective tissue capsule + Schwann cell lamellae

�� lowlow--frequency vibrations (30frequency vibrations (30––50 Hz) 50 Hz) –– rough objectsrough objects

�� Pacinian corpusclesPacinian corpuscles�� less frequent (20% of hand)less frequent (20% of hand)

�� inner core of membrane lamellae inner core of membrane lamellae →→ fluid fluid →→ outer lamellaouter lamella

�� highhigh--frequency vibrations (250frequency vibrations (250––350 Hz) 350 Hz) →→ fine texturesfine textures

�� MerkelMerkel’’s diskss disks�� epidermal (20% of hand)epidermal (20% of hand)

�� light pressure light pressure -- discrimination of shapes, edgesdiscrimination of shapes, edges

�� RuffiniRuffini’’s corpuscless corpuscles�� deep in the skin + in ligaments & tendonsdeep in the skin + in ligaments & tendons

�� sensitive to the cutaneous stretching produced by digit or limb sensitive to the cutaneous stretching produced by digit or limb movementsmovements

Purves, et al, Neuroscience, 3rd ed.

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

Receptive fields & adaptation

rapidly-adapting slowly-adapting rapidly-adapting slowly-adapting

epidermis

dermis

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

Afferent pathways for mechanosensory

information

�� The The dorsal columndorsal column––medial lemniscusmedial lemniscus (DC(DC--ML) ML)

pathway pathway →→ touch & touch & proprioceptionproprioception

�� Spinothalamic (Spinothalamic (anterolateralanterolateral, AL) pathway , AL) pathway →→ pain pain

& temperature& temperature

�� Trigeminothalamic tractsTrigeminothalamic tracts

Two somatosensory pathwaysTwo somatosensory pathways

Somatosensory system Somatosensory system –– general features general features

of pathwaysof pathways

�� Common feature of two pathwaysCommon feature of two pathways

�� 33--neuronal systemsneuronal systems

�� firstfirst--order afferent fiberorder afferent fiber

�� secondsecond--order neuron projecting to contralateral order neuron projecting to contralateral

thalamusthalamus

�� thirdthird--order neuron projecting to Sorder neuron projecting to S--I (S1) cortexI (S1) cortex

�� Topographic (somatotopic) organizationTopographic (somatotopic) organization

DRG (dorsal root ganglion) neuronDRG (dorsal root ganglion) neuron

pseudounipolar cellpseudounipolar cell

peripheralperipheral

processprocess

centralcentral

processprocess

cell body cell body

in DRGin DRG

11stst--order neuron for somatosensory pathwaysorder neuron for somatosensory pathways

telodendrontelodendron

Modality: Discriminative Touch Sensation (include Vibration) and

Conscious Proprioception (Position Sensation, Kinesthesia)

from body

Receptor: Most receptors except free nerve endings

1st Neuron: Dorsal Root Ganglion

Dorsal column (spinal white matter)

2nd Neuron: Dorsal Column Nuclei (Nucleus Gracilis et Cuneatus)

Internal arcuate fiber - Lemniscal decussation - Medial lemniscus

3rd Neuron: Thalamus (VPLc)

Internal capsule ----- Corona radiata

Termination: Primary Somesthetic Area (S I)

Modality: Modality: Discriminative Touch Sensation (include Vibration) and Discriminative Touch Sensation (include Vibration) and

Conscious Proprioception (Position SensaConscious Proprioception (Position Sensation, Kinesthesia)tion, Kinesthesia)

from bodyfrom body

Receptor: Receptor: Most receptors except free nerve endingsMost receptors except free nerve endings

11stst Neuron: Neuron: Dorsal Root GanglionDorsal Root Ganglion

Dorsal column (spinal white matter)Dorsal column (spinal white matter)

22ndnd Neuron: Neuron: Dorsal Column NucleiDorsal Column Nuclei (Nucleus Gracilis et Cuneatus)(Nucleus Gracilis et Cuneatus)

Internal Internal arcuatearcuate fiber fiber -- Lemniscal decussation Lemniscal decussation -- Medial lemniscusMedial lemniscus

33rdrd Neuron: Neuron: Thalamus (VPLc)Thalamus (VPLc)

Internal capsule Internal capsule ---------- Corona radiataCorona radiata

Termination: Termination: Primary Somesthetic Area (S I)Primary Somesthetic Area (S I)

Dorsal ColumDorsal Colum--Medial Medial LemniscalLemniscal (DC(DC--ML) ML)

PathwayPathway

Touch and ProprioceptionTouch and Proprioception

�� Dorsal Column/Medial LemniscusDorsal Column/Medial Lemniscus pathwaypathway

�� ModalitiesModalities

�� light touchlight touch

�� vibrationvibration

�� proprioceptionproprioception

Touch and Proprioception

Dorsal Columns/Medial Lemniscal System

Origin: Dorsal root ganglion (cervical or lumbar)

Course: Fasiculus gracilis/cuneatus

Termination: Nucleus cuneatus (upper body)

Nucleus gracilis (lower body)

Laterality: IPSI

Fasiculus gracilis

(lower body)

Fasiculus cuneatus

(upper body)

Neuron #1

Dorsal Columns/Medial Lemniscal System

Origin: Dorsal root ganglion (cervical or lumbar)

Course: Fasiculus gracilis/cuneatus

Termination: Nucleus cuneatus (upper body)

Nucleus gracilis (lower body)

Laterality: IPSI

Fasiculus gracilis

(lower body)

Fasiculus cuneatus

(upper body)

Neuron #1

Dorsal Columns/ Medial Lemniscal System

Origin: Nucleus gracilis/cuneatusCourse: Medial LemniscusTermination: VPL of ThalamusLaterality: CONTRA

Neuron #2

Nucleus

gracilis

Nucleus

cuneatus

Internal

Arcuate

Fibers

Medial

Lemniscus

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

Origin: Nucleus gracilis/cuneatus

Course: Medial Lemniscus

Termination: VPL of Thalamus

Laterality: CONTRA

Neuron #2

Medial

Lemniscus

Cuneatus

Gracilis

Note: Headnot representedin the ML

Laterality: CONTRA

Neuron #2

Laterality: CONTRA

Neuron #2

Laterality: CONTRA

Neuron #2

Laterality: CONTRA

Neuron #2

Laterality: CONTRA

Neuron #2

Nucleus of

Thalamus

To primary

somatosensory

cortex

Origin: VPL of Thalamus

Course: Posterior Limb Internal Capsule

Termination: Primary Somatosensory Cortex (BA3,1,2)

Laterality: IPSI

Neuron #3

DRG: Dorsal Root GanglionDRG: Dorsal Root Ganglion

1. 1. Posterior White ColumnPosterior White Column

A. Nucleus gracilisA. Nucleus gracilis

B. Nucleus cuneatusB. Nucleus cuneatus

2. 2. Medial LemniscusMedial Lemniscus

3. 3. Corona Radiata Corona Radiata

C. Thalamus (VPLc)C. Thalamus (VPLc)

D. Cerebral Cortex (S I)D. Cerebral Cortex (S I)

DCDC--ML PathwayML Pathway

Modality: Pain & Temperature Sensation,

Light Touch from body

Receptor: Free Nerve Ending

1st Neuron: Dorsal Root Ganglion

2nd Neuron: Dorsal Horn (Lamina I, IV, V)

Anterior white commissure

Spinothalamic tract (Spinal Lemniscus)

3rd Neuron: Thalamus (VPLc & CL)

Modality: Modality: Pain & Temperature Sensation, Pain & Temperature Sensation,

Light Touch Light Touch from bodyfrom body

Receptor: Receptor: Free Nerve Ending Free Nerve Ending

11stst Neuron: Neuron: Dorsal Root GanglionDorsal Root Ganglion

22ndnd Neuron: Neuron: Dorsal Horn Dorsal Horn (Lamina I, IV, V)(Lamina I, IV, V)

Anterior white commissureAnterior white commissure

Spinothalamic tract (Spinal Lemniscus)Spinothalamic tract (Spinal Lemniscus)

33rdrd Neuron: Neuron: Thalamus (VPLc & CL)Thalamus (VPLc & CL)

Spinothalamic tract (AL system)Spinothalamic tract (AL system)

Pain and TemperaturePain and Temperature

�� Anterolateral (Ventrolateral)Anterolateral (Ventrolateral) System System

((==Spinothalamic tract)Spinothalamic tract)

�� ModalitiesModalities

�� painpain

�� temperaturetemperature

Pain and Temperature(Anterolateral system)

Origin: DRG

Course: Dorsal root

Termination: Substantia gelatinosa

Laterality: IPSI

Neuron #1

Substantia gelatinosa

Small diameter primary

afferent fiber

Origin: Lamina I or V

Course: Ventral White Commissure,

Spinothalamic Tract

Termination: VPL of the Thalamus

Laterality: CONTRA

Ventral White Commissure

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Laterality: CONTRA

Neuron #2

Spinothalamic Tract

Origin: VPL Thalamus

Course: Posterior Limb of Internal Capsule

Termination: Primary Somatosensory Cortex (BA 3,1,2)

Laterality: IPSI

Neuron #3

VPL Nucleus

of Thalamus

To primary

somatosensory

cortex

Origin: VPL Thalamus

Course: Posterior Limb of Internal Capsule

Termination: Primary Somatosensory Cortex (BA 3,1,2)

Laterality: IPSI

Neuron #3

DRG: Dorsal Root GanglionDRG: Dorsal Root Ganglion

A. Spinal Dorsal HornA. Spinal Dorsal Horn

B. Reticular FormationB. Reticular Formation

1. 1. Neospinothalamic TractNeospinothalamic Tract

2. 2. Paleospinothalamic TractPaleospinothalamic Tract

C. Thalamus (VPLc, CL)C. Thalamus (VPLc, CL)

3. 3. Corona RadiataCorona Radiata

D. Cerebral Cortex (S I)D. Cerebral Cortex (S I)

Spinothalamic tractSpinothalamic tract

AL SystemAL System

AL systemAL system

Additional AL system pathways:Additional AL system pathways:�� SpinoreticularSpinoreticular →→ RAS (awaking in RAS (awaking in

response to pain stimuli)response to pain stimuli)

�� SpinomesencephalicSpinomesencephalic →→periaqueductal gray (pain control)periaqueductal gray (pain control)

�� SpinotectalSpinotectal →→ superior colliculussuperior colliculus((turning the upper body, head, and turning the upper body, head, and eyes ineyes in the direction of a painful the direction of a painful stimulusstimulus))

�� SpinohypothalamicSpinohypothalamic –– autonomic autonomic response to nociceptionresponse to nociception

DC-ML vs AL systems

Pinprick, heat and cold testingVibration, two-point discrimination,

stereognosis

Tests for function

SlowFastSpeed of

transmission

MultisynapticTwo or three synapses to cortexSynaptic chain

Pain, temperature, crude touch,

visceral pain

Fine touch, joint sensation, vibrationSensation

transmitted

Small-diameter primary afferentsLarge-diameter primary afferentsDiameter of nerve

Multimodal (several sensations

carried in one fiber system)

Each sensation carried separately;

precise localization of sensation

Specificity of signal

conveyed

Small and largeSmallSize of receptive

fields

Ventral and ventrolateral funiculiDorsal and dorsolateral funiculiCourse in spinal

AL PathwayDC-ML PathwayVariable

Face innervation Face innervation →→ CN VCN V

Modality: General Sensation from face

Receptor: Most receptors in the face

1st Neuron: Trigeminal (semilunar) ganglia

2nd Neuron: Trigeminal sensory nucleus (principal)

pain & temperature ---- Spinal trigeminal nucleus

Ventral and Dorsal trigeminothalamic tracts

3rd Neuron: Thalamus (VPM)

Modality: Modality: General SensationGeneral Sensation from facefrom face

Receptor: Receptor: Most receptors in the face Most receptors in the face

11stst Neuron: Neuron: Trigeminal (Trigeminal (semilunarsemilunar) ganglia) ganglia

22ndnd Neuron: Neuron: Trigeminal sensory nucleus (principal)Trigeminal sensory nucleus (principal)

pain & temperaturepain & temperature -------- Spinal trigeminal nucleusSpinal trigeminal nucleus

Ventral and Dorsal trigeminothalamic tractsVentral and Dorsal trigeminothalamic tracts

33rdrd Neuron: Neuron: Thalamus (VPM)Thalamus (VPM)

Trigeminal system Trigeminal system --

Trigeminothalamic tractsTrigeminothalamic tracts

Trigeminothalamic Trigeminothalamic

TractsTracts

A. trigeminal ganglionA. trigeminal ganglion

B. trigeminal sensory B. trigeminal sensory

nucleusnucleus

C. thalamus (VPM)C. thalamus (VPM)

D. cerebral cortex (S I)D. cerebral cortex (S I)

1. 1. spinal tract of spinal tract of

trigeminal nervetrigeminal nerve

2. 2. ventral ventral

trigeminothalamic tracttrigeminothalamic tract

3. 3. dorsal dorsal

trigeminothalamic tracttrigeminothalamic tract

4. 4. corona radiatacorona radiata

V.V. trigeminal nervetrigeminal nerve

Ventral TTT

(contralateral)

Dorsal TTT

(ipsilateral)

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

Summary of trigeminal sensory nucleiSummary of trigeminal sensory nuclei

�� Mechanoreceptive afferent fibers Mechanoreceptive afferent fibers →→ principalprincipal sensory nucleussensory nucleus

�� Pain & temperaturePain & temperature →→ spinalspinaltrigeminaltrigeminal nucleusnucleus

�� PProprioceptive afferent fibers roprioceptive afferent fibers ((jaw musclesjaw muscles) ) →→ mesencephalic mesencephalic trigeminal nucleus trigeminal nucleus ((the only the only primary sensory neurons with primary sensory neurons with cell bodies located incell bodies located in CNS!!!)CNS!!!)

Trigeminal

Mesencephalic

Principal

Spinal

Jaw jerk reflex Jaw jerk reflex –– CN VCN V

Proprioceptive fibers to the mesencephalic nucleus convey pressuProprioceptive fibers to the mesencephalic nucleus convey pressure and re and

kinesthesia from the teeth, periodontium, hard palate, and jointkinesthesia from the teeth, periodontium, hard palate, and joint capsules as well as capsules as well as

impulses from stretch receptors in the muscles of mastication. Timpulses from stretch receptors in the muscles of mastication. The mesencephalic he mesencephalic

nucleus is concerned with mechanisms that control the force of tnucleus is concerned with mechanisms that control the force of the bite. he bite.

CN V: TrigeminalCN V: Trigeminal -- 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

The mesencephalic

above the level of CN VOrigin: Mesencephalic Nucleus of V

The mesencephalic

above the level of CN V

Origin: Mesencephalic Nucleus of V

CN V: TrigeminalCN V: Trigeminalmotor and principal sensory nuclei (level of CN V)motor and principal sensory nuclei (level of CN V)

Sensory

nucleus

CN V: TrigeminalCN V: TrigeminalSpinal nucleus and tract at level of VI/VIISpinal nucleus and tract at level of VI/VII

Neuron #1

Origin: Trigeminal(Gasserian) Ganglion

Course: All branches of Trigeminal Nerve, Spinal Trigeminal tract

Termination: Spinal Nucleus of V

Laterality: Ipsilateral

CN V: TrigeminalCN V: TrigeminalSpinal nucleus and tract at level of XSpinal nucleus and tract at level of X

Neuron #1

CN V: TrigeminalCN V: TrigeminalSpinal nucleus and tract at level of motor decus.Spinal nucleus and tract at level of motor decus.

Neuron #1

CN V: VTTTCN V: VTTTNeuron #2

Origin: Spinal Nucleus of V

Course: VTTT, withMedial Lemniscus

Termination: VPM Thalamus

Laterality: Contralateral

Ventral Trigeminothalamic

Tract (trigeminal lemniscus)

Medial

lemniscus

Medial

lemniscus

Caudal medulla

Rostral medulla

Neuron #2

Origin: Spinal Nucleus of V and Chief Sensory Nuc.

CN V: VTTTCN V: VTTT

Medial

lemniscus

Medial

lemniscus

Caudal pons

Rostral pons

Ventral Trigeminothalamic

Tract (trigeminal lemniscus)

Neuron #2

Origin: Spinal Nucleus of V and Chief Sensory Nuc.

CN V: VTTTCN V: VTTT

Thalamus

Ventral Posteromedial

(VPM) Nucleus

Trigeminal pathways arrive at VPMTrigeminal pathways arrive at VPM

Trigeminal NeuralgiaTrigeminal Neuralgia

(tic douloureux)(tic douloureux)

-- excruciating episodic painexcruciating episodic pain

in the area supplied by in the area supplied by

trigeminal nerve, especiallytrigeminal nerve, especially

second and third divisionsecond and third division

-- trigger pointtrigger point

-- intense pain makes theintense pain makes the

patient grimace (tic)patient grimace (tic)

-- antiepileptic drugantiepileptic drug ((phenytoinphenytoin,,

carbamazepinecarbamazepine) is effective) is effective

-- surgical treatmentsurgical treatment

Herpes Zoster (Shingles)

Herpes Zoster Herpes Zoster

(Shingles)(Shingles) Zoster ophthalmicusZoster Zoster ophthalmicusophthalmicus

�� VaricellaVaricella--zoster virus reactivation from the dorsal root gangliazoster virus reactivation from the dorsal root ganglia

�� Unilateral vesicular eruption within a dermatomeUnilateral vesicular eruption within a dermatome

OOrganization of rganization of somatosensorysomatosensory pathways pathways

Lower-level decussation

Upper-level decussation

Clinical caseClinical case

�� A 21 yr old male is seen weaving his motorcycle in A 21 yr old male is seen weaving his motorcycle in and out of traffic. Unfortunately, he spins out and and out of traffic. Unfortunately, he spins out and smashes his lower back against the curbsmashes his lower back against the curb

�� Several months after the accident, the male has loss Several months after the accident, the male has loss of discriminative touch, vibration and of discriminative touch, vibration and proprioception in proprioception in oneone leg and pain and temperature leg and pain and temperature sensation in the sensation in the otherother legleg

�� Explanation Explanation →→ BrownBrown--SSééquard syndromequard syndrome

Brown-Séquard syndrome

�� DCDC--ML system ML system –– ipsilateral damageipsilateral damage

�� AL system AL system –– contralateral damagecontralateral damage

(DC-ML system)

(AL system)

lesion

Fast & Slow PainFast & Slow Pain

Fast Pain Slow Pain

Sharp, pricking Dull, burning

Group III (Aδδδδ) 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

AL system carries both fast and slow painAL system carries both fast and slow pain

Spinothalamic TractSpinothalamic Tract

& Spinoreticular Tract& Spinoreticular Tract

Widespread Widespread

cortical regioncortical region

CL (CL (intralaminarintralaminar

thalamic nuclei)thalamic nuclei)

reticulothalamicreticulothalamic

pathwayspathways

spinoreticularspinoreticular

tracttract

Primary MotorPrimary Motor

Area (M I)Area (M I)

VPLc (VPLc (ventrobasalventrobasal

nuclear complex)nuclear complex)

(spinal lemniscus)(spinal lemniscus)

spinothalamicspinothalamic

tracttract

thalamus

reticular

formation

NeoSTTNeoSTT PaleoSTTPaleoSTT

Spinal

Reticular

Formation

Medial

thalamus

Lateral

thalamus

Association

cortex

Somato-sensorycortex

Sensation

Affect

Paleospinothalamic

Neospinothalamic

Spinothalamic pain pathways

Nociceptive afferent fibers terminate on projection neurons

in the dorsal horn of the spinal cord

Descending systems modulate the transmission of

ascending pain signals

Kandel, Schwartz, Jessell; Principles of

Neural Science, 4th ed.

Descending analgesic pathways activate enkephalin-

containing local circuit neurons

SER, NA

Glu, NP

Endogenous opioid peptides arise from three large

precursor polyproteins

opiumopium

Analgesia Analgesia -- enkephalin & morphineenkephalin & morphine

Sensory input Sensory input + opiates/opioids

morphine

Visceroceptive pathways (mainly nociceptive)Visceroceptive pathways (mainly 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

Examples of referred pain

Primary somatosensory cortex (SPrimary somatosensory cortex (S--I, S1)I, S1)

Somatotopic mapping

Somatosensory homunculusSomatosensory homunculus

Homunculus is based on peripheral receptor density → greatest area to fingers,

Each of the four areas of the primary somatic sensory Each of the four areas of the primary somatic sensory

cortex (3a, 3b, 1, and 2) receives input from all areas of cortex (3a, 3b, 1, and 2) receives input from all areas of

the body surface, but one modality tends to dominate in the body surface, but one modality tends to dominate in

each area each area

�� 3a 3a -- from proprioceptors signaling muscle stretch from proprioceptors signaling muscle stretch

�� 3b & 13b & 1-- from cutaneous mechanoreceptorsfrom cutaneous mechanoreceptors

�� 2 2 –– from both 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

Thalamus

Layer 4

Layer 5

Layer 3S-II

Contralateral S-I

Organization of S-I

Kandel, Schwartz, Jessell; Principles of Neural

Science, 4th ed.

Connections between cortical areas represent stages of

information processing. At each stage progressively more

abstract information is extracted from the sensory stimulus.

Ascending sensory pathways

Spinocerebellar tracts → unconcious proprioception

Modality: Modality: Unconscious Proprioception Unconscious Proprioception

Receptor: Receptor: Muscle spindle, Golgi tendon organMuscle spindle, Golgi tendon organ

11stst Neuron: Neuron: Dorsal Root Ganglion Dorsal Root Ganglion

Posterior Root , [Posterior Column]Posterior Root , [Posterior Column]

22ndnd Neuron: Neuron: 1. Clarke1. Clarke’’s column s column

Posterior SCbTPosterior SCbT

2. Accessory 2. Accessory CuneateCuneate NucleusNucleus

Cuneocerebellar tractCuneocerebellar tract

3. Posterior Horn3. Posterior Horn

Anterior SCbTAnterior SCbT

Termination: Termination: Cerebellar CortexCerebellar Cortex

Spinocerebellar tracts (SCbT)Spinocerebellar tracts (SCbT)

MMuscle spindleuscle spindless

�� IIntrafusal ntrafusal

muscle fibers muscle fibers

�� CConnective onnective

tissuetissue capsulecapsule

Intrafusal

fibersExtrafusal

Extrafusal

Capsule

Golgi tendon organsGolgi tendon organs

�� Collagenous fibers parallel Collagenous fibers parallel

to the extrafusal muscle to the extrafusal muscle

fibersfibers

�� UUnmyelinated nerve nmyelinated nerve

terminalsterminals

�� CConnective tissueonnective tissue capsulecapsule

PPosterior osterior SCbT & cuneocerebellar tractSCbT & cuneocerebellar tract -- ipsilateralipsilateral

Cuneocerebellar tract

Posterior SCbT

Information about phase, rate, and

strength of muscle contraction

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

Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT

thru ICP

AnteriorAnterior SCbT SCbT --

contralateralcontralateral

laminae V-VII

Information related to

interneuronal activity and

the effectiveness of

descending pathways

Posterior SCbTPosterior SCbT

ICPICP

post. SCbT andpost. SCbT and

cuneocerebellarcuneocerebellar

tracttract

posteriorposteriorwhite columnwhite column

posterior rootposterior root

Anterior SCbTAnterior SCbT

SCPSCP

anterioranterior

spinocerebellarspinocerebellar

tracttract

anterior whiteanterior white

commissurecommissure

posterior rootposterior root

Anterior Anterior vsvs Posterior SCbTPosterior SCbT

FriedreichFriedreich’’s Ataxias Ataxia

posterior spinocerebellar tract lesion posterior spinocerebellar tract lesion -- cerebellar ataxiacerebellar ataxia

Patients tend to walk with a wide base, stagger, and frequently fall

Motoneuron DRG

From sensing to respondingFrom sensing to responding

Functional systems in CNS

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