The Spinal CordThe Spinal Cord
Basic NeuroscienceBasic Neuroscience
James H. Baños, Ph.D.James H. Baños, Ph.D.
Grey and White Grey and White MatterMatter
Grey and White MatterGrey and White Matter
Grey Matter = Cell Body
White Matter = Myelinated axon
Grey and White MatterGrey and White Matter
Grey matterGrey matter CortexCortex Nucleus (CNS)Nucleus (CNS) Ganglion (PNS) Exception: Basal Ganglion (PNS) Exception: Basal
GangliaGanglia
Grey and White MatterGrey and White Matter White MatterWhite Matter
Nerve (PNS)Nerve (PNS) Tract (CNS)Tract (CNS) Fasciculus/Funiculus -- Group of fibers with common origin Fasciculus/Funiculus -- Group of fibers with common origin
and destinationand destination Lemniscus -- Ribbon-like fiber tractLemniscus -- Ribbon-like fiber tract Peduncle -- Massive group of fibers -- usually several tractsPeduncle -- Massive group of fibers -- usually several tracts
Grey and White MatterGrey and White Matter Tracts are named with origin first, then Tracts are named with origin first, then
destinationdestination Corticospinal tract -- cortex to spinal cordCorticospinal tract -- cortex to spinal cord Mammilothalamic tract -- Mammilary bodies to Mammilothalamic tract -- Mammilary bodies to
thalamusthalamus Spinocerebellar tract -- Spinal cord to Spinocerebellar tract -- Spinal cord to
cerebellumcerebellum Corticobulbar tract -- Cortex to brain stemCorticobulbar tract -- Cortex to brain stem
The Spinal CordThe Spinal Cord
General OrganizationGeneral Organization
Spinal cord is SMALL!Spinal cord is SMALL! 42-45 cm long42-45 cm long 1 CM wide at widest point1 CM wide at widest point Does not extend all the way to the bottom of the spinal Does not extend all the way to the bottom of the spinal
columncolumn Pattern of grey/white matter is reversed in the Pattern of grey/white matter is reversed in the
cordcord White matter tracts on outsideWhite matter tracts on outside Grey matter on the insideGrey matter on the inside Staining reverses this!!!Staining reverses this!!!
General OrganizationGeneral Organization
White matter (tractsof axons)
Grey Matter(cell bodies)
General OrganizationGeneral Organization
Spinal cord is segmented anatomicallySpinal cord is segmented anatomically Input and output occurs in groups of Input and output occurs in groups of
rootlets arranged in a series rootlets arranged in a series longitudinally along the cordlongitudinally along the cord Dorsal rootlets -- Input -- carry sensory Dorsal rootlets -- Input -- carry sensory
informationinformation Ventral rootlets -- Output -- motor neuronsVentral rootlets -- Output -- motor neurons
General OrganizationGeneral Organization
Each set of rootlets forms a spinal Each set of rootlets forms a spinal nerve that innervates a nerve that innervates a corresponding segment of the body, corresponding segment of the body, called a called a dermatomedermatome
General OrganizationGeneral Organization
General OrganizationGeneral Organization
There are 31 segments in the spinal There are 31 segments in the spinal cord:cord: 8 cervical (C1 - C8)8 cervical (C1 - C8) 12 Thoracic (T1 - T12)12 Thoracic (T1 - T12) 5 Lumbar (L1 - L5)5 Lumbar (L1 - L5) 5 Sacral (S1 - S5)5 Sacral (S1 - S5) 1 Coccygeal1 Coccygeal
General OrganizationGeneral Organization
The spinal cord is housed within the The spinal cord is housed within the vertebral columnvertebral column
General OrganizationGeneral Organization
Each cord segment has Each cord segment has a corresponding a corresponding vertebra of the same vertebra of the same name (e.g., C3)name (e.g., C3)
Spinal nerves enter/exit Spinal nerves enter/exit underneath their underneath their corresponding corresponding vertebral segmentvertebral segment
General OrganizationGeneral Organization
But wait! Something doesn’t add up!But wait! Something doesn’t add up! How can spinal nerves exit below their How can spinal nerves exit below their
corresponding vertebral segment if the corresponding vertebral segment if the cord is only 42cm-45cm long?cord is only 42cm-45cm long?
Answer: Spinal nerves extend down to Answer: Spinal nerves extend down to the appropriate vertebral segment the appropriate vertebral segment forming the forming the cauda equinacauda equina
This means cord segments and This means cord segments and vertebral segments don’t line upvertebral segments don’t line up
General OrganizationGeneral Organization
General OrganizationGeneral Organization
Cord is not of uniform thickness Cord is not of uniform thickness throughout its length. Why not?throughout its length. Why not?
General OrganizationGeneral Organization
Cord is not of uniform thickness Cord is not of uniform thickness throughout its length. Why not?throughout its length. Why not?
Answer: Answer: Segments of the cord innervate parts of Segments of the cord innervate parts of
the body that differ in complexitythe body that differ in complexity There are fewer white matter tracts There are fewer white matter tracts
lower in the cord. lower in the cord.
General OrganizationGeneral Organization
Cervical enlargementC5 - T1
Lumbar enlargementL2 - S3
The Spinal Cord The Spinal Cord in Cross Sectionin Cross Section
Cord SectionsCord Sections
Segments of the spinal cord have a Segments of the spinal cord have a similar organization, but vary in similar organization, but vary in appearance. appearance.
Always know where you are in the Always know where you are in the cord (i.e., cervical, thoracic, lumbar, cord (i.e., cervical, thoracic, lumbar, sacral) sacral)
Cord Sections -- CervicalCord Sections -- Cervical
Cervical cord is Cervical cord is wide, flat, almost wide, flat, almost oval in appearance. oval in appearance. Why? Why?
Cord Sections -- Cervical Cord Sections -- Cervical EnlargementEnlargement
Cervical
Cervical Enlargement
What’s different What’s different about the cervical about the cervical enlargement . Why? enlargement . Why?
Cord Section -- ThoracicCord Section -- Thoracic
Less White matter Less White matter than cervicalthan cervical
Rounder Rounder appearanceappearance
Less prominent Less prominent ventral horns than ventral horns than cervical cervical enlargementenlargement
Cord Section -- LumbarCord Section -- Lumbar
Less White matter Less White matter than thoracicthan thoracic
Rounder Rounder appearanceappearance
Larger ventral Larger ventral horns, especially in horns, especially in lumbar lumbar enlargementenlargement
Lumbar
Lumbar Enlargement
Cord Section -- SacralCord Section -- Sacral
Not much white Not much white mattermatter
Mostly grey, Mostly grey, although not much although not much of that eitherof that either
Cross Sectional OrganizationCross Sectional Organization
Anterior median fissure
Anterior white commisure
Posterior median sulcusPosterior intermediate sulcus
Tract ofLissauer
Grey MatterGrey Matter
LaminarLaminar Laminae of Laminae of
RexedRexed
Grey MatterGrey Matter
Posterior Posterior (dorsal) Horn(dorsal) Horn
Intermediate Intermediate GreyGrey
Anterior Anterior (ventral) Horn(ventral) Horn
Grey Matter: Posterior HornGrey Matter: Posterior Horn
Mostly Mostly InterneuronsInterneurons Substantia Substantia
gelatinosagelatinosa Pain/temp procPain/temp proc
Body of the Body of the posterior hornposterior horn
Sensory procSensory proc
Grey Matter: Intermediate GreyGrey Matter: Intermediate Grey
Clarke’s ColumnClarke’s Column T1-L3T1-L3 Balance/proprio.Balance/proprio.
Intermediolateral Intermediolateral ColumnColumn T1-L3T1-L3 Sympathetic Sympathetic
neuronsneurons
Grey Matter: Anterior HornGrey Matter: Anterior Horn
Lower Motor Lower Motor NeuronsNeurons
Corticospinal tract
Dorsal Columns
Spinothalamic tract
Spinocerebellar tracts
White Matter: The “Big Four” White Matter: The “Big Four” PathwaysPathways
The Big FourThe Big Four
Corticospinal tractCorticospinal tract Voluntary motorVoluntary motor
Dorsal columns/ medial lemniscusDorsal columns/ medial lemniscus Discriminative touchDiscriminative touch Conscious proprioceptionConscious proprioception
Spinocerebellar tract (dorsal and ventral)Spinocerebellar tract (dorsal and ventral) Unconscious proprioceptionUnconscious proprioception
Spinothalamic tractSpinothalamic tract Pain/temperaturePain/temperature
Corticospinal Corticospinal TractTract
Voluntary MotorVoluntary Motor
Corticospinal TractCorticospinal Tract
First order neuron (upper motor neuron) First order neuron (upper motor neuron) originates in precentral gyrusoriginates in precentral gyrus
Passes through internal capsulePasses through internal capsule 90% decussates in caudal medulla90% decussates in caudal medulla
Lateral corticospinal tractLateral corticospinal tract 10% undecussated10% undecussated
Anterior corticospinal tractAnterior corticospinal tract Synapses on second order neuron (lower motor Synapses on second order neuron (lower motor
neuron) in ventral gray of the cordneuron) in ventral gray of the cord Second order neuron innervates muscleSecond order neuron innervates muscle
Motor HomunculusMotor Homunculus
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Motor HomonculusMotor Homonculus
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Arms Legs
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Corticospinal TractCorticospinal Tract
Spinal CordMedulla Pons Midbrain
Upper & Lower Motor NeuronsUpper & Lower Motor Neurons Upper Motor NeuronUpper Motor Neuron
Motor Cortex to Ventral Grey HornMotor Cortex to Ventral Grey Horn Modulatory influence on stretch reflex Modulatory influence on stretch reflex
arcarc Lower Motor NeuronLower Motor Neuron
Ventral Grey Horn to Neuromuscular Ventral Grey Horn to Neuromuscular JunctionJunction
Efferent of stretch reflex arcEfferent of stretch reflex arc Helps maintain toneHelps maintain tone
Sensory NeuronSensory Neuron Stretch receptors in muscle and tendonsStretch receptors in muscle and tendons Helps maintain toneHelps maintain tone Afferent of basic stretch reflex arcAfferent of basic stretch reflex arc
Motor Ctx
VentralGrey Horn
UMN
LMN
Upper & Lower Motor NeuronsUpper & Lower Motor Neurons Maintenance of ToneMaintenance of Tone
Input from stretch receptors Input from stretch receptors causes lower motor neuron to causes lower motor neuron to supply tonic stimulation to the supply tonic stimulation to the musclemuscle
The upper motor neuron The upper motor neuron modulates this -- will tend to modulates this -- will tend to “override” the tonic signal “override” the tonic signal from the sensory neuron from the sensory neuron
UMN
LMN
Upper & Lower Motor NeuronsUpper & Lower Motor Neurons Reflex ArcReflex Arc
Afferent is sensory neuron Afferent is sensory neuron detecting a sudden stretchdetecting a sudden stretch
Signal is strong and results in Signal is strong and results in a strong response by the lower a strong response by the lower motor neuronmotor neuron
Strong signal usually Strong signal usually overcomes mild cortical input overcomes mild cortical input from the UMN from the UMN
UMN
LMN
Upper & Lower Motor NeuronsUpper & Lower Motor Neurons Upper Motor Neuron SignsUpper Motor Neuron Signs
Spastic paresisSpastic paresis HypertoniaHypertonia HyperreflexiaHyperreflexia No muscle atrophy (until perhaps late in No muscle atrophy (until perhaps late in
the course)the course) Positive Babinski Positive Babinski
Why?Why? Loss of voluntary UMN signalLoss of voluntary UMN signal Loss of modulation of tone and reflexes Loss of modulation of tone and reflexes
by UMN -- the circuit runs uncheckedby UMN -- the circuit runs unchecked
Motor Ctx
VentralGrey Horn
UMN
LMN
Upper & Lower Motor NeuronsUpper & Lower Motor Neurons Lower Motor Neuron SignsLower Motor Neuron Signs
Flaccid paresis/paralysisFlaccid paresis/paralysis Muscle fasciculationsMuscle fasciculations HypotoniaHypotonia HyporeflexiaHyporeflexia Muscle atrophyMuscle atrophy Negative Babinski Negative Babinski
Why?Why? Loss of LMN for voluntary movementLoss of LMN for voluntary movement Loss of efferent component of reflex arc Loss of efferent component of reflex arc
and tone pathwayand tone pathway
Motor Ctx
VentralGrey Horn
UMN
LMN
Babinski’s SignBabinski’s Sign
In response to stimulation of the sole of In response to stimulation of the sole of the foot, the toes will usually curl the foot, the toes will usually curl downward.downward.
When UMN inhibition is removed, the When UMN inhibition is removed, the toes will curl upward (Dorsiflexion). This toes will curl upward (Dorsiflexion). This is referred to as a is referred to as a positive Babinskipositive Babinski or or presence of Babinski’s sign.presence of Babinski’s sign.
Related Terms…Related Terms…
Spasticity -- Increased muscle tone Spasticity -- Increased muscle tone and increased reflex contraction and increased reflex contraction (UMN)(UMN)
Clonus -- Rythmic contractions and Clonus -- Rythmic contractions and relaxations seen when a spastic relaxations seen when a spastic muscle is stretched (UMN)muscle is stretched (UMN)
Basics of LocalizationBasics of Localization
If all limbs are checked for upper If all limbs are checked for upper and lower motor neuron signs, you and lower motor neuron signs, you can begin to localize lesionscan begin to localize lesions
Left-right differences are also very Left-right differences are also very importantimportant
Dorsal Column/ Dorsal Column/ Medial Medial
LemniscusLemniscusDiscriminative TouchDiscriminative Touch
Conscious ProprioceptionConscious Proprioception
Dorsal Columns/Medial LemniscusDorsal Columns/Medial Lemniscus
First order neuron begins in receptorFirst order neuron begins in receptor Enters cord at tract of LissauerEnters cord at tract of Lissauer Legs run in fasciculus gracilis (medial dorsal)Legs run in fasciculus gracilis (medial dorsal) Arms run in fasciculus cuneatus (lateral dorsal)Arms run in fasciculus cuneatus (lateral dorsal) Synapse on nucleus gracilis and nucleus Synapse on nucleus gracilis and nucleus
cuneatus (caudal medulla)cuneatus (caudal medulla) 2nd order neuron decussates and runs from NG 2nd order neuron decussates and runs from NG
& NC to thalamus (as medial lemniscus)& NC to thalamus (as medial lemniscus) 3rd order neuron runs from thalamus to 3rd order neuron runs from thalamus to
postcentral gyruspostcentral gyrus
Dorsal Columns/Medial LemniscusDorsal Columns/Medial Lemniscus
Spinal CordMedulla Pons Midbrain
Spinocerebellar Spinocerebellar TractsTracts
Unconscious ProprioceptionUnconscious Proprioception
Dorsal (Posterior) Spinocerebellar Dorsal (Posterior) Spinocerebellar TractTract
Involves Clark’s Column, a longitudinal gray Involves Clark’s Column, a longitudinal gray matter body from about T1 to L3matter body from about T1 to L3
Below Clark’s Column:Below Clark’s Column: Runs with f. cuneatus, synapses in Clark’s Column, Runs with f. cuneatus, synapses in Clark’s Column,
joins dorsal spinocerebellar tractjoins dorsal spinocerebellar tract Level of Clark’s ColumnLevel of Clark’s Column
Synapses in Clark’s Column, joins dorsal Synapses in Clark’s Column, joins dorsal spinocerebellar tractspinocerebellar tract
Above Clark’s ColumnAbove Clark’s Column Runs with f. cuneatus, synapses in lateral cuneate Runs with f. cuneatus, synapses in lateral cuneate
nucleus (caudal medulla), projects to ipsilateral nucleus (caudal medulla), projects to ipsilateral cerebellumcerebellum
Dorsal (Posterior) Spinocerebellar Dorsal (Posterior) Spinocerebellar TractTract
Spinal CordMedulla Pons Midbrain
To Cerebellum
L3 T1
Ventral (Anterior) Spinocerebellar Ventral (Anterior) Spinocerebellar TractTract
Supplements Dorsal Spinocerebellar TractSupplements Dorsal Spinocerebellar Tract Information from more diverse array or Information from more diverse array or
receptorsreceptors Originates from scattered cells in the Originates from scattered cells in the
intermediate grey caudal to L1 (which in intermediate grey caudal to L1 (which in turn have input from proprioceptive axons turn have input from proprioceptive axons or their collateralsor their collaterals
Crosses Crosses twicetwice, to end up in ipsilateral , to end up in ipsilateral cerebellumcerebellum
Ventral (Anterior) Spinocerebellar Ventral (Anterior) Spinocerebellar TractTract
Spinal CordMedulla Pons Midbrain
Spinothalamic Spinothalamic TractTract
Pain and TemperaturePain and Temperature
Spinothalamic TractSpinothalamic Tract
First order neurons originate in pain receptors, First order neurons originate in pain receptors, enter cord at tract of Lissauer, and synapse in enter cord at tract of Lissauer, and synapse in substantia gelatinosa or nucleus propriussubstantia gelatinosa or nucleus proprius
Second order neurons cross at the anterior white Second order neurons cross at the anterior white commissure, rising 1 or 2 cord levels in the commissure, rising 1 or 2 cord levels in the process, and form contralateral spinothalamic process, and form contralateral spinothalamic tracttract
A third order neuron (not technically A third order neuron (not technically spinothalamic tract) projects to the cortexspinothalamic tract) projects to the cortex
Spinothalamic TractSpinothalamic Tract
Spinothalamic TractSpinothalamic Tract
Spinal CordMedulla Pons Midbrain
L1
L2
L3
L4
L5
L1
L2
L3
L4
L5
Coming Up…Coming Up…
Lab Week Overview: MondayLab Week Overview: Monday Virtual LabsVirtual Labs Wet lab day: ThursdayWet lab day: Thursday Lab Practical Exam: FridayLab Practical Exam: Friday