Functional systems in CNS
Transcript of 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
Somatosensation - receptors
reading Braille
MeissnerMeissner’’s corpuscles corpuscle
epidermis
dermis
Glabrous skin
250-300 Hz – “vibration/tickle”Pacinian Corpuscles – Rapidly adapting
Somatosensation - receptors
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
Somatosensation - receptors
epidermis
dermis
Glabrous skin
Static/directional stretch of skinRuffini’s Corpuscles – Slowly adapting
Somatosensation - receptors
RuffiniRuffini’’s endings ending
epidermis
dermis
Glabrous skin
Free nerve endings – Pain/temperature
Somatosensation - receptors
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
Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed.
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
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
Touch and Proprioception
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
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
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
Medial
Lemniscus
Cuneatus
Gracilis
Note: Headnot representedin the ML
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: Nucleus gracilis/cuneatus
Course: Medial Lemniscus
Termination: VPL of Thalamus
Laterality: CONTRA
Neuron #2
VPL
Nucleus of
Thalamus
To primary
somatosensory
cortex
Touch and Proprioception
Dorsal Columns/ Medial Lemniscal System
Origin: VPL of Thalamus
Course: Posterior Limb Internal Capsule
Termination: Primary Somatosensory Cortex (BA3,1,2)
Laterality: IPSI
Neuron #3
ATL
F
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
DRG
D
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)
Internal capsule ----- Corona radiata
Termination: Primary Somesthetic Area (S I)
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)
Internal capsule Internal capsule ---------- Corona radiataCorona radiata
Termination: Termination: Primary Somesthetic Area (S I)Primary Somesthetic Area (S I)
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
Pain and Temperature(Anterolateral system)
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
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
Origin: Lamina I or V
Course: Ventral White Commissure,
Spinothalamic Tract
Termination: VPL of the Thalamus
Laterality: CONTRA
Neuron #2
Spinothalamic Tract
Pain and Temperature(Anterolateral system)
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
Pain and Temperature(Anterolateral system)
Origin: VPL Thalamus
Course: Posterior Limb of Internal Capsule
Termination: Primary Somatosensory Cortex (BA 3,1,2)
Laterality: IPSI
Neuron #3
ATL
F
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
DRG
D
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
fiber
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
cord
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)
Internal capsule ----- Corona radiata
Termination: Primary Somesthetic Area (S I)
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)
Internal capsule Internal capsule ---------- Corona radiataCorona radiata
Termination: Termination: Primary Somesthetic Area (S I)Primary Somesthetic Area (S I)
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
CN V: TrigeminalCN V: Trigeminal -- mesencephalicmesencephalic
The mesencephalic
nucleus and tract run
above the level of CN VOrigin: Mesencephalic Nucleus of V
Course: Mesencephalic tract of V
Termination: Motor Nucleus of V
Laterality: Bilateral
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
CN V: TrigeminalCN V: Trigeminalmotor and principal sensory nuclei (level of CN V)motor and principal sensory nuclei (level of CN V)
Chief
Sensory
nucleus
of V
Motor
nucleus
of V
ALAR
BASAL
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
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 motor decus.Spinal nucleus and tract at level of motor decus.
Neuron #1
Origin: Trigeminal(Gasserian) Ganglion
Course: All branches of Trigeminal Nerve, Spinal Trigeminal tract
Termination: Spinal Nucleus of V
Laterality: Ipsilateral
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
VTTT
VTTT
Neuron #2
Origin: Spinal Nucleus of V and Chief Sensory Nuc.
Course: VTTT, withMedial Lemniscus
Termination: VPM Thalamus
Laterality: Contralateral
CN V: VTTTCN V: VTTT
Medial
lemniscus
Medial
lemniscus
VTTT
VTTT
Caudal pons
Rostral pons
Ventral Trigeminothalamic
Tract (trigeminal lemniscus)
Neuron #2
Origin: Spinal Nucleus of V and Chief Sensory Nuc.
Course: VTTT, withMedial Lemniscus
Termination: VPM Thalamus
Laterality: Contralateral
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
Cord
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
Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed.
Descending systems modulate the transmission of
ascending pain signals
Kandel, Schwartz, Jessell; Principles of
Neural Science, 4th ed.
Purves, et al, Neuroscience, 3rd ed.
Descending analgesic pathways activate enkephalin-
containing local circuit neurons
Purves, et al, Neuroscience, 3rd ed.
SER, NA
Glu, NP
Endogenous opioid peptides arise from three large
precursor polyproteins
Kandel, Schwartz, Jessell; Principles of
Neural Science, 4th ed.
opiumopium
Analgesia Analgesia -- enkephalin & morphineenkephalin & morphine
Sensory input Sensory input + opiates/opioids
Kandel, Schwartz, Jessell; Principles of
Neural Science, 4th ed.
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
Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed.
Examples of referred pain
Purves, et al, Neuroscience, 3rd ed.
(red)
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,
lips
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
Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed.
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.
Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed.
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
fiber
Extrafusal
fiber
Extrafusal
fiber
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
(ICP)
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
Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT
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
Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT
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
Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT
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
Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT
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
Posterior (Dorsal) SCbTPosterior (Dorsal) SCbT
AnteriorAnterior SCbT SCbT --
contralateralcontralateral
(SCP)
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