The Spinal Cord The Spinal Cord Basic Neuroscience James H. Baños, Ph.D.

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

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